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Modeling of 2D PV Devices

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Contents

Note[edit]

This is a literature review page to take optical and electrical parameters from existing 2D PV devices at the lab scale and scale them up to make a theoretical module. Then do simulation on them e.g. AOI, antireflection coating etc. in something like pvlib to provide system designers with the new module. It would be our pleasure if you share your experience in this area with us. (Discussion tab is top left of this page)


Background[edit]

Electric Field Effect in Atomically Thin Carbon Films [1][edit]

What is a 2D material?: 2D materials refer to crystalline, generally single atom thin materials which are covalently bonded (in plane bonding) to perform a strong single layer and then weakly bonded, generally Van der Waals bonding, to the next layer (out of plane bonding) to make it easy to exfoliate from each other without destroying the single layer crystalline structure. 2D material can be made of one element or a compound of two or more elements. Graphene (single layer of graphite) is the first and the most studied 2D material. Although Graphene was explored first by Wallance in 1947 however it never been physically made till 2004 by Novoselov and Geim who won a Physics noble prize for this discovery. Geim used mechanical exfoliation technique using scotch tape to separate graphite layers to end up by single layer graphene.

  • Few Layer Graphene (FLG) size was up to 10 um and for thicker film ~ 3nm size reached to 100 um
  • FLG were put into multiterminal Hall bar devices on top of SiO2 and applied Vg to investigate electronic properties
  • Dependence of resistivity on Vg and charge transport is being done by Shubnikov-de Haas (ShdH) oscillations studies


Electronics based on two-dimensional materials [2][edit]

Abstract The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal–oxide–semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.

Literature Review[edit]

The reflectivity spectra of some group VA transition metal dichalcogenides [3][edit]

Abstract: This paper investigate reflectivity spectra from basal planes of these crystal structure of VA TMDCs; 2H-NbSe2, 2H-Tase2, 2H-TaS2 and 1T-TaS2 for energy range between 25 meV and 14 eV in two different temperature room temperature and 77K. In continue they did Kramers-Kronig analysis and band band models for these materials discussed. 2H-NbSe2, 2H-Tase2, 2H-TaS2 are metallic because half filled d band and 1T-TaS2 showing semiconductor behavior at room T.

  • reflectivity spectra measured for all 4 materials from 0.025 eV to 30 eV at room temp and 77K
  • very sharp peak measured for all 4 materials in low energy (<2eV)
  • Optical parameters of all 4 materials provided

1.real and imaginary parts of dielectric function at room temperature

2.real and imaginary parts of dielectric function at 77 K

3.absorption coefficient

4.energy-loss function

5.oscillator sum integral neff(E)

Electrodeposited semiconducting molybdenum selenide films. II. Optical, electrical, electrochemical and photoelectrochemical solar cell studies [4][edit]

Abstract: MoSe2 was electrodeposited and optical, electrical and electrochemical behaviors studied. optical absorption defined an indirect bandgap material with BG=1.14 eV. Electrical conductivity at various T showed impurity conduction and existance of deep level traps. Mott-Schottky plots for type of semiconductor and parameters like ND, Ec and Ev. the J-V graphs from electrochemical studies show charge transfer at interface is due valence band and it also involves surface states. They use electrodeposition to deposit MoSe2 in fabrication of photoelectrochemical solar cell. In this type of solar cell charge transfer take place at semiconductor- electrolyte interface and produce photocurrent. Films deposited on conducting glass plates to study optical absorption behavior.

  • optical absorption graph showed very broad peaks because electrodeposited is polycrystalline and weak absorption because of thin layer (1.1 um). absorption spectra confirm indirect spectra
  • Film deposited on Ti substrate as back contact and silver dots for front contact studied for Electrical conductivity. They performed ohmic contact
  • I-V curve shows linear behavior (Ohm's law) for lower voltages which become nonlinear for higher voltages after filling of a discrete set of traps.
  • Electrochemical characterization showed n-type behavior ND= 10 e15
  • The efficiency of this solar cell was measured very low because of these reasons (1)Low film thickness (1.1 um) causing small number of e-h pairs. (2) existance of high density traps at the surface and deep (3) film was not uniform

* They used a multilayer film of MoSe2 so in result was an indirect material (direct bandgap behavior was not discovered yet)Italic text

MS2 (M = W, Mo) photosensitive thin films for solar cells [5][edit]

Abstract: WS2 and MoS2 photosensitive films deposited by sputtering on 10-20 nm thick Ni layer and then crystallization process by annealing at 1073K for 30min. two different technique for film deposition ; MoS2: Solid State Reaction WS2: reactive sputtering

  • X-ray diffraction pattern for both films obtained indicating basal plane crystalline with a sharp peak
  • XPS spectra for both films studied
  • Optical absorption spectra and photoconductivity for both films studied
  • analyzing all data showed film properties was independent to deposition technique and thin layer of Ni and annealing on 1073 K played the most important role to make poly crystalline structure with big enough grain boundaries to obtain photocurrent. Thin Ni layer caused Metal Induced Crystallization process I believe It also made a textured pattern on the surface


Graphene‐On‐Silicon Schottky Junction Solar Cells [6][edit]

Abstract:

  • Deposit Graphene Sheets (GS) on n-Si wafer with average PCE 1.5%
  • multilayer graphene to reach higher mobility
  • GS form a Schottky junction with n-Si
  • GS work also as ARC with reducing reflection 70% visible and 80% near IR
  • efficiency drops with thicker film, more recombination occurs
  • there is a trade off between conductivity and transparency


Monolayer graphene film/silicon nanowire array Schottky junction solar cells [7][edit]

Abstract: Schottky junction solar cells were constructed by combining the monolayer graphene (MLG) films and the Si nanowire (SiNW) arrays. Pronounced photovoltaic characteristics were investigated for devices with both p-MLG/n-SiNWs and n-MLG/p-SiNWs structures. Due to the balance between light absorption and surface carrier recombination, devices made of SiNW arrays with a medium length showed better performance and could be further improved by enhancing the MLG conductivity via appropriate surface treatment or doping. Eventually, a photoconversion efficiency up to 2.15% is obtained by the means of filling the interspace of SiNW array with graphene suspension.

  • 8 different structure examined, highest PCE= 2.15% with garaphene suspension filling the gaps between NWs
  • Table 1 in the page 133113-2 summarize all 8 different structures

Graphene based Schottky junction solar cells on patterned silicon-pillar-array substrate [8][edit]

Abstract: Graphene-on-silicon Schottky junction solar cells were prepared with pillar-array-patterned silicon substrate. Such patterned substrate showed an anti-reflective characteristic and led to an absorption enhancement of the solar cell, which showed enhanced performance with short-circuit current density, open-circuit voltage, fill factor, and energy conversion efficiency of 464.86 mV, 14.58 mA/cm2, 0.29, and 1.96%, respectively. Nitric acid was used to dope graphene film and the cell performance showed a great improvement with efficiency increasing to 3.55%. This is due to the p-type chemical doping effect of HNO3 which increases the work function and the carrier density of graphene.

  • Chemical doping of graphene
  • They showed doping of graphene by HNO3 for 15s enhance the PCE from 1.96% to 3.55%
  • Table I in the page 233505-2 summarize all experimental data

High Efficiency Graphene Solar Cells by Chemical Doping [9] [edit]

Abstract: We demonstrate single layer graphene/n-Si Schottky junction solar cells that under AM1.5 illumination exhibit a power conversion efficiency (PCE) of 8.6%. This performance, achieved by doping the graphene with bis(trifluoromethanesulfonyl)amide, exceeds the native (undoped) device performance by a factor of 4.5 and is the highest PCE reported for graphene-based solar cells to date. Current−voltage, capacitance−voltage, and external quantum efficiency measurements show the enhancement to be due to the doping-induced shift in the graphene chemical potential that increases the graphene carrier density (decreasing the cell series resistance) and increases the cell’s built-in potential (increasing the open circuit voltage) both of which improve the solar cell fill factor.

  • Chemical doping the graphene with bis(trifluoromethanesulfonyl)amide (TFSA)
  • doping reduces Graphene's sheet resistance and then Rs is reduced and in result built in potential increased so more efficiently e-h generated pares are separated

Molybdenum disulphide/titanium dioxide nanocomposite-poly 3-hexylthiophene bulk heterojunction solar cell [10][edit]

Abstract:

Hybrid bulk heterojunction (BHJ) PV using MoS2/TiO2 nanocomposite (~15um) and poly 3-hexylthiophene (P3HT) active layers is studied in this paper. MoS2 shows direct bandgap (1.85 eV) and indirect in multi layer (1.2 eV)

  • bulk MoS2 grinded and solved in acetonitrile and sonicated to produce ultrathin nanoflakes, TiO2 nanoparticles and MoS2 mixed in 2:1 ratio and deposited on ITO coated glass. Then front contact formation and annealing was performed at 450 C for 30 min. 1 wt% of P3HT in chlorobenzene was spin coated onto MoS2/TiO2 composite film. The P3HT diffuse into porous TiO2 network and form a BHJ. Back contact was performed by 50 nm Gold deposition (e-beam).
  • surface SEM image shows highly porous and randomly textured surface
  • Raman spectrum obtained. peaks confirm TiO2 and MoS2 materials
  • Energy band diagram of TiO2/MoS2/P3HT is shown, claimed P3HT is mainly used for charge separation by forming BHJ with large surface porous TiO2/MoS2 nanocomposite
  • I-V curve of device under dark and illumination is shown also semi log plot of the dark I-V curve is shown
  • External Quantum efficiency (EQE) in the range of 350-800 nm measured, showing maximum value of %61 at 485 nm.

Photonic design principles for ultrahigh-efficiency photovoltaics [11][edit]

Abstract: This paper focus on some new approaches of light management to minimize thermodynamic losses and reach to ultrahigh efficiencies. Entropic loss result in a systematic reduction of 400-500 mV in Voc for all practical solar-cell materials which indicate rooms for efficiency improvement. they trying to reach above %40 efficiency for a single junction solar cell by light management which was only possible previously with a triple junction solar cells.

  • Some approaches in light management are; 3 dimensional parabolic light reflectors, planar metamaterials, Mie-scattering surface nanostructure, metal-dielectric-metal or semiconductor-dielectric-semiconductor waveguide
  • multi-junction solar cell instead of single junction to minimize carrier thermalization and absorb most energy from solar spectrum
  • Series multi-junction structure has couple of disadvantages; fabrication complexity, current matching among the subcells is required (subcell generating the lowest current limits the overall multi-junction cell current), lattice match for different layer is also required
  • Alternating approach will by multi-junction in parallel array with spectrum-splitting photonic structure. In this approach a light splitting layer will filter the solar spectrum to that particular wavelength (bandgap) that underneath device is designed for.
  • In conclusion, using photonics structures for light managing inside the solar cells has a lot to improve the efficiency and not that much left in material science part of solar cells

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides [12][edit]

Abstract: This paper review applications of Transition metal dichalcogenides (TMDCs) in different devices such as transistors, photodetectors and PV devices. TMDCs materials have indirect Bandgap in bulk and multilayer structure however they go to direct Bandgap in single layer and sometimes in few layers structure. The bandgap of TMDCs are also sizabale around 1-2 eV by engineering the substrate or doping. TMDCs have MX2 structure and depending on the choose of elements can be semiconducting or metallic Electrical behavior. Generally MoX2 and WX2 shows semiconducting behavior and NbX2 and TaX2 are more metallic. The advantages of using TMDCs in PV devices are: the work functions of TMDCs and edges are compatible with commonly used electrodes. next advantage is to engineering the bandgap of each layer and build a heterojunction solar cell structure to harvest maximum energy from light. This structure potentially can be used to adsorb from visible to nearIR range.

  • Introducing TMDCs materials as 2D material
  • Discussing the physics of TMDCs (Band structure, Band gab, mobility etc.)
  • various approach for synthesis of TMDCs (Top down methods, and Bottom-up methods)
  • Applications such as PV, Photodetectors, LEDs, molecular sensors, flexible and transparent briefly discussed


High Efficiency Graphene Solar Cells by Chemical Doping [13] [edit]

Abstract:

  • Deposit Graphene Sheets (GS) on n-Si wafer with average PCE 1.5%
  • multilayer graphene to reach higher mobility
  • GS form a Schottky junction with n-Si
  • GS work also as ARC with reducing reflection 70% visible and 80% near IR
  • efficiency drops with thicker film, more recombination occurs
  • there is a trade off between conductivity and transparency

Graphene-based Schottky junction solar cells [14][edit]

Abstract: The Schottky junction, with merits of material universality, low cost and easy fabrication, is an alternative structure for solar cells. Compared to traditional indium-tin-oxide (ITO) based Schottky junction solar cells, graphene-based ones have merits of low cost, performance stability, and are applicable to flexible devices. In this highlight, we survey the recent research on graphene-based Schottky junction solar cells, including graphene-on-silicon Schottky junction solar cells and graphene/single NW (NB) Schottky junction solar cells. The working principle of them is discussed. These works demonstrate that graphene-based Schottky junction structures are promising candidates for developing diverse novel high-efficient and low-cost photovoltaic devices. The perspective and challenge of them are also discussed and anticipated.

  • Not new information, doesn't worth to read, small review of previous work on Graphene-based Schottky junction PV

Colloidal Antireflection Coating Improves Graphene–Silicon Solar Cells [15][edit]

Abstract: Carbon nanotube-Si and graphene-Si solar cells have attracted much interest recently owing to their potential in simplifying manufacturing process and lowering cost compared to Si cells. Until now, the power conversion efficiency of graphene-Si cells remains under 10% and well below that of the nanotube-Si counterpart. Here, we involved a colloidal antireflection coating onto a monolayer graphene-Si solar cell and enhanced the cell efficiency to 14.5% under standard illumination (air mass 1.5, 100 mW/cm2) with a stable antireflection effect over long time. The antireflection treatment was realized by a simple spin-coating process, which significantly increased the short-circuit current density and the incident photon-to-electron conversion efficiency to about 90% across the visible range. Our results demonstrate a great promise in developing high-efficiency graphene-Si solar cells in parallel to the more extensively studied carbon nanotube-Si structures.

  • they add TiO2 (nanoparticles 3-5 nm) ARC by spin-coating
  • there are some cracks on surface make it possible for acid treatment
  • without encapsulation after 20 days it degraded and PCE dropped from 14.1% to 6.5% because the loss of HNO3 doping effect
  • HNO3 vapor re-treatment recovered PCE to 14.5%

Graphene/semiconductor heterojunction solar cells with modulated antireflection and graphene work function [16][edit]

Abstract: In this paper, a theoretical model is presented to simulate the performance of graphene/semiconductor heterojunction solar cells. Using parameters extracted from experiments, our simulation gives consistent results with tested performance. two practical optimization treatments have been proposed.

  • First, the work function (WF) and layer number of graphene should be carefully adjusted. by applying an electric field or chemical doping and number of graphene layers
  • Second, antirefection (AR) layers should be introduced to mitigate the energy dissipation from the optical refection. polish Si reflect 35% of visible. Pillar array introduced to reduce reflection to 0.01%
  • To verify the simulation result, To verify the simulation result, solar cells based on acid modified graphene films and/or silicon pillar arrays were assembled, tested, and were found to deliver improved efficiencies of up to 7.7%
  • Table I and Table II in page 113 summarize simulation parameters and experimental test results respectively

High-efficiency graphene/Si nanoarray Schottky junction solar cells via surface modification and graphene doping [17][edit]

Abstract: In this work, we conducted a comprehensive study on high-efficiency graphene/Si nanoarray Schottky junction solar cells. Besides the Si nanowire (SiNW) array, a Si nanohole (SiNH) array was first used for the device construction since it showed the advantages in terms of larger effective junction area while enhanced light absorption is retained. It was found that surface charge recombination as well as graphene conductivity and work function played important roles in determining the solar cell performance. By suppressing the surface recombination with appropriate surface passivation, together with the careful control of the graphene layer number and the doping level, we found that the device performance can be significantly improved. Eventually, by inserting a thin conducting polymer poly(3-hexylthiophene) (P3HT) as the electron blocking layer between Si nanoarrays and graphene films, maximum power conversion efficiencies (PCEs) of 8.71% and 10.30% were demonstrated for the devices based on SiNW and SiNH arrays, respectively, as a result of reduced carrier recombination in the anode. The PCEs demonstrated in this work are the highest values achieved thus far for the graphene/Si nanoarray solar cells. The present results suggest great potential of the graphene/Si nanoarrays as high-efficiency and low-cost photovoltaic devices.

  • SiNH showed some superior result over SiNWs
  • Passivation/modification on the Si nanoarrays, together with the careful control of the graphene layer number and the doping time, maximum PCE values of 8.71% and 10.30% were achieved for the SiNW array and SiNH array based photovoltaic devices, respectively.
  • Table 1 in page 6598 summarize studied devices and Table 2 in page 6599 summarize degradation
  • The devices also exhibited excellent stability in air and remained stable after one week's storage in air.

Performance Enhancement of a Graphene-Zinc Phosphide Solar Cell Using the Electric Field-Effect [18][edit]

Abstract: The optical transparency and high electron mobility of graphene make it an attractive material for photovoltaics. We present a field-effect solar cell using graphene to form a tunable junction barrier with an Earth-abundant and low cost zinc phosphide (Zn3P2) thin-film light absorber. Adding a semitransparent top electrostatic gate allows for tuning of the graphene Fermi level and hence the energy barrier at the graphene-Zn3P2 junction, going from an ohmic contact at negative gate voltages to a rectifying barrier at positive gate voltages. We perform current and capacitance measurements at different gate voltages in order to demonstrate the control of the energy barrier and depletion width in the zinc phosphide. Our photovoltaic measurements show that the efficiency conversion is increased 2-fold when we increase the gate voltage and the junction barrier to maximize the photovoltaic response. At an optimal gate voltage of +2 V, we obtain an open-circuit voltage of Voc = 0.53 V and an efficiency of 1.9% under AM 1.5 1-sun solar illumination. This work demonstrates that the field effect can be used to modulate and optimize the response of photovoltaic devices incorporating graphene.

  • in terms of Graphene PV, this is not efficient as previous work but is new field effect solar cell is optimized by gate voltage
  • graphene doping, gate dielectric could be tested

Monolayer MoS2 Heterojunction Solar Cells [19][edit]

Abstract: We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photogenerated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%, which is the highest efficiency among all monolayer transition-metal dichalcogenide-based solar cells. The demonstrated results of monolayer MoS2/Si-based solar cells hold the promise for integration of 2D materials with commercially available Si-based electronics in highly efficient devices.

  • they did no passivation/ modification on Si surface before MoS2 transfer!
  • 15nm Al deposited on top of MoS2 ans charge collector (semi transparent) and 100 nm Al as electrode as top conact

Light Generation and Harvesting in a van der Waals Heterostructure [20][edit]

Abstract: Two-dimensional (2D) materials are a new type of materials under intense study because of their interesting physical properties and wide range of potential applications from nanoelectronics to sensing and photonics. Monolayers of semiconducting transition metal dichalcogenides MoS2 or WSe2 have been proposed as promising channel materials for field-effect transistors. Their high mechanical flexibility, stability, and quality coupled with potentially inexpensive production methods offer potential advantages compared to organic and crystalline bulk semiconductors. Due to quantum mechanical confinement, the band gap in monolayer MoS2 is direct in nature, leading to a strong interaction with light that can be exploited for building phototransistors and ultrasensitive photodetectors. Here, we report on the realization of light-emitting diodes based on vertical heterojunctions composed of n-type monolayer MoS2 and p-type silicon. Careful interface engineering allows us to realize diodes showing rectification and light emission from the entire surface of the heterojunction. Electroluminescence spectra show clear signs of direct excitons related to the optical transitions between the conduction and valence bands. Our pn diodes can also operate as solar cells, with typical external quantum efficiency exceeding 4%. Our work opens up the way to more sophisticated optoelectronic devices such as lasers and heterostructure solar cells based on hybrids of 2D semiconductors and silicon.

  • Not that much relevant to our topic
  • focus mostly on LED and photodetector

Flexible Graphene Electrode-Based Organic Photovoltaics with Record-High Efficiency [21][edit]

Abstract Advancements in the field of flexible high-efficiency solar cells and other optoelectronic devices will strongly depend on the development of electrode materials with good conductivity and flexibility. To address chemical and mechanical instability of currently used indium tin oxide (ITO), graphene has been suggested as a promising flexible transparent electrode, but challenges remain in achieving high efficiency of grahene-based polymer solar cells (PSCs) compared to their ITO-based counterparts. Here we demonstrate graphene anode- and cathode based flexible PSCs with record-high power conversion efficiencies of 6.1% and 7.1%, respectively. The high efficiencies were achieved via thermal treatment of MoO3 electron blocking layer and direct deposition of ZnO electron transporting layer on graphene. We also demonstrate graphene-based flexible PSCs on polyethylene naphthalate substrates and show the device stability under different bending conditions. Our work paves a way to fully graphene electrode-based flexible solar cells using a simple and reproducible process.

  • graphene Cathode based and Anode Based PSCs tried, MoO3 was used in both structure as electron blocking to prevent recombination
  • 3 monolayers graphene is used
  • Same structure tried by ITO, very close PCE tested
  • Both structure fabricated on polyethylene naphthalate (PEN) and tested PCE=6.1% for Anode & PCE=7.1% for cathode
  • performance remain the same up to 100 tensile flexing cycles

Stability of graphene–silicon heterostructure solar cells [22][edit]

Abstract: The stability of undoped graphene–silicon heterostructure solar cells was investigated. Single-layer graphene was grown by chemical vapor deposition on copper foil. Prior to the transfer of graphene to the silicon wafer, the flat Si(111) surface was passivated with hydrogen or methyl groups (CH3). The conversion efficiency, h, of the H terminated Si device was negligible small (0.1%), whereas that of the CH3 passivated Si was 2 and 4.2% at 100mW (AM 1.5) and 20mW of light intensity, respectively. After 28 days in ambient atmosphere h decreased only slightly to 1.5 and 3.7%. This small change of h is due to the high stability of the CH3 passivated graphene– Si(111) interface. The methylated Si surface shows a high degree of chemical stability especially during the graphene transfer process.

  • graphene cannot placed directly on Si, dangling bonds will destroy monolayer graphene properties. This is due to a reduced interface defect-density.
  • Graphene and Si interface is investigated by comparing two different methods for si passivation; H-termination and methyl (CH3) while methylated showed much better result


Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics [23][edit]

Abstract: Graphene and transition metal dichalcogenides (TMDCs) are the two major types of layered materials under intensive investigation. However, the zero-bandgap nature of graphene and the relatively low mobility in TMDCs limit their applications. Here we reintroduce black phosphorus (BP), the most stable allotrope of phosphorus with strong intrinsic in-plane anisotropy, to the layered-material family. For 15-nm-thick BP, we measure a Hall mobility of 1,000 and 600cm2V-1 s-1 for holes along the light (x) and heavy (y) effective mass directions at 120 K. BP thin films also exhibit large and anisotropic in-plane optical conductivity from 2 to 5 mm. Field-effect transistors using 5 nm BP along x direction exhibit an on–off current ratio exceeding 105, a field-effect mobility of 205cm2V-1 s- 1, and good current saturation characteristics all at room temperature. BP shows great potential for thin-film electronics, infrared optoelectronics and novel devices in which anisotropic properties are desirable

  • This paper look physical, electrical, and optical properties of BP
  • It has angle-dependent optical conductivity

Role of Interfacial Oxide in High-Efficiency Graphene–Silicon Schottky Barrier Solar Cells [24][edit]

Abstract: The advent of chemical vapor deposition (CVD) grown graphene has allowed researchers to investigate large area graphene/n-silicon Schottky barrier solar cells. Using chemically doped graphene, efficiencies of nearly 10% can be achieved for devices without antireflective coatings. However, many devices reported in past literature often exhibit a distinctive s-shaped kink in the measured I/V curves under illumination resulting in poor fill factor. This behavior is especially prevalent for devices with pristine (not chemically doped) graphene but can be seen in some cases for doped graphene as well. In this work, we show that the native oxide on the silicon presents a transport barrier for photogenerated holes and causes recombination current, which is responsible for causing the kink. We experimentally verify our hypothesis and propose a simple semiconductor physics model that qualitatively captures the effect. Furthermore, we offer an additional optimization to graphene/n-silicon devices: by choosing the optimal oxide thickness, we can increase the efficiency of our devices to 12.4% after chemical doping and to a new record of 15.6% after applying an antireflective coating.

  • Si native oxide layer thicker than 15 A make recombination issue cannot solved by graphene doping.
  • Native SiO2 thickness=10A 1 hour after HF dip and 20A after 1 week

Interface designed MoS2/GaAs heterostructure solar cell with sandwich stacked hexagonal boron nitride [25][edit]

Abstract: MoS2 is a layered two-dimensional semiconductor with a direct band gap of 1.8 eV. The MoS2/ bulk semiconductor system offers a new platform for solar cell device design. Different from the conventional bulk p-n junctions, in the MoS2/bulk semiconductor heterostructure, static charge transfer shifts the Fermi level of MoS2 toward that of bulk semiconductor, lowering the barrier height of the formed junction. Herein, we introduce hexagonal boron nitride (h-BN) into MoS2/GaAs heterostructure to suppress the static charge transfer, and the obtained MoS2/h-BN/GaAs solar cell exhibits an improved power conversion efficiency of 5.42%. More importantly, the sandwiched h-BN makes the Fermi level tuning of MoS2 more effective. By employing chemical doping and electrical gating into the solar cell device, PCE of 9.03% is achieved, which is the highest among all the reported monolayer transition metal dichalcogenide based solar cells.

The photovoltaic performance of the heterojunction is greatly influenced by the junction barrier height, which means suppressing the static charge transfer between 2D materials and semiconductor substrate are highly desirable. Herein, we introduce 2D hexagonal boron nitride (h-BN) into the MoS2/GaAs heterostructure to suppress the static charge transfer. More importantly, the inserted h-BN layer makes the tuning of Fermi level of MoS2 more effective, which greatly improves the performance of solar cells.

  • GaAs passivated by NH3 plasma 5 min
  • Both structures tested, with and without hBN layer
  • In this study, AuCl3 solution in nitromethane (1 mM) is used to doping 2D MoS2 to increase the PCE of the MoS2/h-BN/GaAs solar cell. this chemical doping enhanced PCE from 5.38% to 7.15%
  • electrical gating even improved from 6.87% to 9.03% with Vg= -1V

18.5% efficient graphene/GaAs van der Waals heterostructure solar cell [26][edit]

Abstract: High efficient solar cell is highly demanded for sustainable development of human society, leading to the cutting-edge research on various types of solar cells. The physical picture of graphene/semiconductor van der Waals Schottky diode is unique as Fermi level of graphene can be tuned by gate structure relatively independent of semiconductor substrate. However, the reported gated graphene/semiconductor heterostructure has power conversion efficiency (PCE) normally less than 10%. Herein, utilizing a designed graphene-dielectric-graphene gating structure for graphene/GaAs heterojunction, we have achieved solar cell with PCE of 18.5% and open circuit voltage of 0.96 V. Drift-diffusion simulation results agree well with the experimental data and predict this device structure can work with a PCE above 23.8%. This research opens a door of high efficient solar cell utilizing the graphene/semiconductor heterostructure.

  • a graphene-dielectric-graphene structure, where the top graphene layer functions as the gating electrode, This structure combines the advantages of anti-reflection property of the dielectric layer, high transparency and highly tunable Fermi level of graphene.
  • graphene transferred on top of GaAs using PMMA, 68 nm of Al2O3 was deposited as ARC layer, extra graphene layer on top of active area as electrode structure and Ag paste in last as electrode
  • active graphene layer was doped by TFSA (bis(trifluoromethanesulfonyl)amide)
  • 1-9 layer Graphene investigated, 3 layer showed max PCE
  • very bad written paper, hard to follow

Functionalized graphene and other two-dimensional materials for photovoltaic devices: device design and processing [27][edit]

Abstract: This is a review paper that focus on application of Graphene, TMDs and black phophorous on various photovoltaic devices such as; organic solar cells, Shottky junction solar cells, dye-sensitized solar cells, quantum dot-sensitized solar cells, some other inorganic solar cells and perovskite solar cells. This paper first introduce mostly used preparation methods such as; Exfoliation methods and CVD methods and then focus on some properties;

Properties[edit]

  • mobility : Generally 2D materials are famous for their very high in plane mobility, This number for graphene is ~ 200 000 cm2V-1 S-1
  • Absorbance: theoretical equation for absorbance of single layer Graphene is presented, absorbance for single layer is ~2.3%, TMDs also showing absorbance 5-10% which is one order of magnitude higher than Si.
  • Conductivity: equation provided. Four layers Graphene has 30 ohm squared cm conductivity but still 90% transmittance which can be a perfect candidate for transparent electrode. TMDs don't have high conductivity because of their semiconducting behavior but because of high mobility and absorbance they can be used as active layer or charge transport layer.
  • Specific surface area: surface area of graphene measured as high as 2150 m2g-1 make graphene as promising electrode material for super-capacitors, solar cells, and sensors

Application in OPVs Graphene is being used in OPVs as transparent electrodes (anode and cathode), electron transport layers (ETLs), hole transport layers (HTLs), n-type acceptors and packaging layers (there is a table of previous work on OPVs) Other PV devices Application of Graphene in other PV devices such as shottky junction solar cell, dye-sensitized solar cells (DSSCs), quantum dot-sensitized solar cells (QDSSCs) and Perovskite solar cells are summarized in a table

Enhanced photovoltaic performances of graphene/Si solar cells by insertion of a MoS2 thin film [28][edit]

Abstract: This paper represent of adding a MoS2 large area CVD grown film to a graphene Si Schottky junction solar cell to improve the efficiency. This extra layer will work as an effective electron-blocking/hole-transporting layer. It is also demonstrated the solar cell efficiency will improve by increasing graphene layer thickness and decreasing MoS2 thickness. Highest efficiency achieved by this structure was 11.1% ; trilayer-graphene/MoS2/n-Si. single layer/bilayer and trilayer graphene/MoS2/ n-Si are compared in performance. The thickness of MoS2 layer kept constant as 17 nm (is not single layer). Trilayer graphene showed better performance compared with others.

Enhanced photon absorption in spiral nanostructured solar cells using layered 2D materials [29][edit]

Abstract: MoS2 can absorb the light but in solar cell, because of its sub-wavelength thickness, only a few percentage of incident light will be absorbed. This paper introduce a spiral structure for MoS2/Graphene/hBN stack to increase optical absorption up to 90%. The thickness of the stack is about 1 um. They investigate Spiral with and without metal contacts to be able to monitor MoS2 influence into the structure more accurately. The thickness of hBN layer has critical role to enhance optical absorption (up to 90%) or the absorption relative to the amount of photoactive material used (up to 762% enhancement)


Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface [30][edit]

Abstract: Two-dimensional transition metal dichalcogenides (TMDCs) such as molybdenum sulfide MoS2 and tungsten sulfide WSe2 have potential applications in electronics because they exhibit high on-off current ratios and distinctive electro-optical properties. Spatially connected TMDC lateral heterojunctions are key components for constructing monolayer p-n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, such structures are not readily prepared via the layer-stacking techniques, and direct growth favors the thermodynamically preferred TMDC alloys. We report the two-step epitaxial growth of lateral WSe2-MoS2 heterojunction, where the edge of WSe2 induces the epitaxial MoS2 growth despite a large lattice mismatch. The epitaxial growth process offers a controllable method to obtain lateral heterojunction with an atomically sharp interface.

  • lateral heterojunctions is challenging because TMDC alloys are thermodynamically preferred and perform alloy in the interface
  • First grow single crystalline triangular WSe2 at 950 and then growth MoS2 in a separate tube at 750 C Mo and S vapor pressure should be in certain range, otherwise will growth vertically or WS2 (page 625 middle column)
  • Calculated PCE=0.2%
  • This paper mostly focused on the fab technique and physics of the device than PV behavior

A Van Der Waals Homojunction: Ideal p–n Diode Behavior in MoSe 2 [31][edit]

Abstract: A MoSe2 p–n diode with a van der Waals homojunction is demonstrated by stacking undoped (n‐type) and Nb‐doped (p‐type) semiconducting MoSe2 synthesized by chemical vapor transport for Nb substitutional doping. The p–n diode reveals an ideality factor of ≈1.0 and a high external quantum efficiency (≈52%), which increases in response to light intensity due to the negligible recombination rate at the clean homojunction interface.

  • MoS2, WS2 and MoSe2 are n-type while WSe2 and MoTe2 are P-type as intrinsic
  • in this study they doped MoSe2 with Nb to make it P-type and make vdW homojunction p-n diode

Combined effect of double antireflection coating and reversible molecular doping on performance of few-layer graphene/n-silicon Schottky barrier solar cells [32][edit]

Abstract: Few layer graphenes were deposited by CVD onto unpolished Cu foils and then transferred to n-type silicon wafer to make graphene/n-silicon Schottky barrier solar cells. Graphene was doped with nitric acid vapor and an antireflection layer was added on top. The total power conversion efficiency reached to 8.5%. It is shown Double layer Anti-reflective Coating (DARC), MgF2/ZnS gives the best results. Graphene/n-Si and DARC/Graphene/n-Si are compared by simulation and demonstration indicating DARC/G/n-Si has the highest efficiency.

Diffractive nanostructures for enhanced light-harvesting in organic photovoltaic devices [33][edit]

Abstract: An in-coupling gratings introduced in this paper to improve performance of thin film organic solar cells. It is claimed this gratings will improve the light absorption of 14.8% and it is independent from active layer. This was applied on blade-coated devices and a 12% improvement in efficiency was measured. 2 dimensional grating yields the best result compared to 1D. This will be compatible with roll-to-roll production for OPVs. Different geometry structures for 1D and 2D examined to reach to optimum design.

Broadband Absorption Enhancement in Solar Cells with an Atomically Thin Active Layer [34][edit]

Abstract: In this paper they are trying to use of resonances made by a photonic crystal slab for broadband enhancement of above bandgap absorption of a single layer MoS2. In this structure design, a single layer MoS2 is placed on top a photonic crystal layer that it sit on top of a mirror. By doing multiple resonances absorption can be improved over the entire frequency range above the bandgap of MoS2. By doing this average absorption reached over 51% for visible spectrum while it is around 10% for single-pass absorption for single layer MoS2. A photonic crystal structure design study was done to find the optimum Lattice Constant, Hole Radius and the Slab thickness to maximize the resonance and light absorption. They comes up with some rules, First; grating period need to be subwavelength to most of the frequency region under interest to eliminate those waves travelling away from active layer and cannot be absorbed. The large holes works better than small holes, Finally thin layer works better than a thick layer. This geometry design is a general design and can be used for other TMDs materials as well.

Angle-selective perfect absorption with two-dimensional materials [35][edit]

Abstract: In this paper is tried to use a simple structure, a mirror, a dielectric spacer and a 2D material on top to enhance the light absorption. In this design, and in 2D material wavelength range which the material has some loss, always there is an angle of incidence that absorption reaches to unity in that angle. They demonstrated this structure can exceed 77% absorption for mid-infrared range (13 um). This was shown for Graphene but it is claimed it works with other 2D materials with different doping levels. It is claimed because this structure is simple and no nano-patterning required, so it can be scaled to large area and high yield production.


Lateral black phosphorene P–N junctions formed via chemical doping for high performance near-infrared photodetector [36][edit]

Abstract: Black phosphorene (BP), a newly discovered elemental two-dimensional material, is attractive for optoelectronic and photonic applications because of its unique in-plane anisotropy, thickness-dependent direct bandgap and high carrier mobility. Since its discovery, black phosphorene has become an appealing candidate well-suited for polarization-resolved near- and mid-infrared optoelectronics due to its relative narrow bandgap and asymmetric structure. Here, we employ benzyl viologen (BV) as an effective electron dopant to part of the area of a (p-type) few-layer BP flake and achieve an ambient stable, inplane P–N junction. Chemical doping with BV molecules modulates the electron density and allows acquiring a large built-in potential in this in-plane BP P–N junction, which is crucial for achieving high responsivity photodetectors and high quantum efficiency solar cells. As a demonstrative example, by illuminating it with a near-infrared laser at 1.47 mm, we observe a high responsivity up to �180 mA/W with a rise time of 15 ms, and an external quantum efficiency of 0.75%. Our strategy for creating environmentally stable BP P–N junction paves the way to implementing high performance BP phototransistors and solar cells, which is also applicable to other 2D materials.

  • the most stable allotrope of element phosphorus with strong anisotropy and a direct bandgap ranging from 0.3 eV to 2 eV depending on # of layers
  • photoresponse in the visible and near infrared ranges
  • they claim PCE=0.75% for power density of 10 W/cm2

Mixed-dimensional van der Waals heterostructures [37][edit]

Abstract: This is a review paper about VdW structure devices using 2D materials (Graphene, hBN or TMDs). VdW structures are 2D-nD (n=0,1 or 3).

  • this paper looks the physics of 2D and heterostructure devices
  • different type of devices such as FET, LED and photodetectors covered in this paper
  • They also looked PV devices.
  • must read PV part in page 176 of journal, a good track provided

Sub-nanometer planar solar absorber [38][edit]

Abstract: This paper focus on a method to optimize solar absorption for 2D material or any sub-namo thickness films using simple planar structures. Two structures offered, sub-nanometer film placed (1) onto a transparent layer on a metallic film or (2) between the transparent layer and the substrate for thr oblique sunlight illumination condition These methodology will give two parameter freedom to enhance the absorption film thickness and incident angle while previous structure had to deal with film thickness only, So can reach to almost perfect absorption.

  • they show in theory and experiment that always there is a pair of transparent layer thickness and incident angle that absorption reach to 100%
  • first they choose a thickness for target wavelength and then find the incident angle to reach 100% absorption
  • they reached 92% absorption my MoS2 at 660 nm
  • the PCE for broadband and wide angle was measured to be 4.4%

Graphene coupled with Pt cubic nanoparticles for high performance, air-stable graphene-silicon solar cells [39][edit]

Abstract:

  • Graphene itself has low carrier concentration and therefore low work function so not good for PV
  • chemical doping is not permanent solution, it degrade fast
  • they add some Pt nano particle onto Gr to enhance solar absorption be Plasmonic effect
  • adding Pt nano particles improved also carrier concentration and work function ( works as physical doping)
  • PCE reached to 7%
  • Adding TiO2 antireflective film enhance PCE to 10%
  • this can be called as 0, 2 and 3 dimensional structure


Single Atomically Sharp Lateral Monolayer p-n Heterojunction Solar Cells with Extraordinarily High Power Conversion Efficiency [40][edit]

Abstract: The recent development of 2D monolayer lateral semiconductor has created new paradigm to develop p-n heterojunctions. Albeit, the growth methods of these heterostructures typically result in alloy structures at the interface, limiting the development for high-efficiency photovoltaic (PV) devices. Here, the PV properties of sequentially grown alloy-free 2D monolayer WSe2-MoS2 lateral p-n heterojunction are explores. The PV devices show an extraordinary power conversion efficiency of 2.56% under AM 1.5G illumination. The large surface active area enables the full exposure of the depletion region, leading to excellent omnidirectional light harvesting characteristic with only 5% reduction of efficiency at incident angles up to 75°. Modeling studies demonstrate the PV devices comply with typical principles, increasing the feasibility for further development. Furthermore, the appropriate electrode-spacing design can lead to environment-independent PV properties. These robust PV properties deriving from the atomically sharp lateral p-n interface can help develop the next-generation photovoltaics.

  • for electronic tuning (doping properties) dual gate tuning being used a lot, but this guys used single back gate tuning to increase active area

High efficiency graphene/MoS2/Si Schottky barrier solar cells using layer-controlled MoS2 films [41][edit]

Abstract: The isolation of two-dimensional (2D) materials and the possibility to assemblage as a vertical heterostructure have significantly promoted the development of ultrathin and flexible devices. Here, we demonstrate the fabrication of high efficiency graphene/MoS2/Si Schottky barrier solar cells with Molybdenum disulfide (MoS2) interlayers. MoS2 monolayers were prepared by sulfurizing pre-annealed molybdenum foil, which allows not only to precisely control the layer number, but also the nondestructive transference onto arbitrary substrates. The inserted MoS2 layers function as hole transport layer to facilitate the separation of electron-hole pairs as well as electron blocking layer to suppress the recombination at graphene/silicon interfaces. By optimizing the thickness of MoS2 layers, a high photovoltaic conversion efficiency of 15.8% was achieved in graphene/MoS2/Si solar cells. This study provides a novel approach for the synthesis of large-area MoS2 monolayers and their potential application for ultrathin and low-cost photovoltaic devices.

  • they deposit pre-annealed Mo foil and the sulurize it
  • MoS2 layer works as hole transport layer, so prevent e-h recombination at Si-Graphene interface
  • By optimizing the thickness of MoS2 layers PCE 15.8% was achieved

Graphene and its derivatives for solar cells application [42][edit]

Abstract: Graphene has played the role of game-changer for conductive transparent devices indebted to its unique two dimensional (2D) structures and gained an exceptional opportunity to be employed in energy industry. In the past two decades graphene has been merged with the concept of photovoltaic (PV) material and exhibited a significant role as a transparent electrode, hole/electron transport material and interfacial buffer layer in solar cell devices. This review covers the different methods of graphene fabrication and broadly discusses the recent advances in graphene-based solar cells, including bulk heterojunction (BHJ) organic, dye-sensitized and perovskite solar cell deices. The power conversion efficiency surpassed 20.3% for graphene-based perovskite solar cells and hit the efficiency of 10% for BHJ organic solar cells. Except the part of charge extracting and transport to the electrodes, graphene has another unique role of device protection against environmental degradation via its packed 2D network structure and provides long-term environmental stability for PV devices. We highlighted a comparative study on the role of graphene and its derivatives in photovoltaic devices. After all, the potential issues and the perspective for future research in graphene-based materials for PV applications are presented.

  • A good review paper
  • Application of graphene-based materials for organic solar cells (OSCs)
  • Graphene-based materials for dye-sensitized solar cells (DSSCs)
  • Graphene-based materials for perovskite solar cells (PSCs)


Doping ZnO Electron Transport Layers with MoS2 Nanosheets Enhances the Efficiency of Polymer Solar Cells [43][edit]

Abstract: In this study, we incorporated molybdenum disulfide (MoS2) nanosheets into sol–gel processing of zinc oxide (ZnO) to form ZnO:MoS2 composites for use as electron transport layers (ETLs) in inverted polymer solar cells featuring a binary bulk heterojunction active layer. We could effectively tune the energy band of the ZnO:MoS2 composite film from 4.45 to 4.22 eV by varying the content of MoS2 up to 0.5 wt %, such that the composite was suitable for use in bulk heterojunction photovoltaic devices based on poly[bis(5-(2-ethylhexyl)thien-2-yl)benzodithiophene-alt-(4-(2-ethylhexyl)-3-fluorothienothiophene)-2-carboxylate-2,6-diyl] (PTB7-TH)/phenyl-C71-butryric acid methyl ester (PC71BM). In particular, the power conversion efficiency (PCE) of the PTB7-TH/PC71BM (1:1.5, w/w) device incorporating the ZnO:MoS2 (0.5 wt %) composite layer as the ETL was 10.1%, up from 8.8% for the corresponding device featuring ZnO alone as the ETL, a relative increase of 15%. Incorporating a small amount of MoS2 nanosheets into the ETL altered the morphology of the ETL and resulted in enhanced current densities, fill factors, and PCEs for the devices. We used ultraviolet photoelectron spectroscopy, synchrotron grazing incidence wide-/small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy to characterize the energy band structures, internal structures, surface roughness, and morphologies, respectively, of the ZnO:MoS2 composite films.

  • In an OPV system, optimizing the active layer is key for obtaining a high power convention efficiency (PCE)
  • by adding MoS2 sheets to ZnO active layer, they showed a PCE increase from 8.8% to 10.1%
  • different concentrations tested, optimum is 0.5 wt%

Tunable black phosphorus heterojunction transistors for multifunctional optoelectronics [44][edit]

Abstract:

Symmetry-Controlled Reversible Photovoltaic Current Flow in Ultrathin All 2D Vertically Stacked Graphene/MoS2/WS2/Graphene Devices [45][edit]

Abstract: Atomically thin vertical heterostructures are promising candidates for optoelectronic applications, especially for flexible and transparent technologies. Here, we show how ultrathin all two-dimensional vertical-stacked type-II heterostructure devices can be assembled using only materials grown by chemical vapor deposition, with graphene (Gr) as top and bottom electrodes and MoS2/WS2 as the active semiconductor layers in the middle. Furthermore, we show that the stack symmetry, which dictates the type-II directionality, is the dominant factor in controlling the photocurrent direction upon light irradiation, whereas in homobilayers, photocurrent direction cannot be easily controlled because the tunnel barrier is determined by the doping levels of the graphene, which appears fixed for top and bottom graphene layers due to their dielectric environments. Therefore, the ability to direct photovoltaic current flow is demonstrated to be only possible using heterobilayers (HBs) and not homobilayers. We study the photovoltaic effects in more than 40 devices, which allows for statistical verification of performance and comparative behavior. The photovoltage in the graphene/transition-metal dichalcogenide-heterobilayer/graphene (Gr/ TMD-HB (MoS2/WS2)/Gr) increases up to 10 times that generated in the monolayer TMD devices under the same optical illumination power, due to efficient charge transfer between WS2 and MoS2 and extraction to graphene electrodes. By applying external gate voltages (Vg), the band alignment can be tuned, which in turn controls the photovoltaic effect in the vertical heterostructures. The tunneling-assisted interlayer charge recombination also plays a significant role in modulating the photovoltaic effect in the Gr/TMD-HB/Gr. These results provide important insights into how layer symmetry in verticalstacked graphene/TMD/graphene ultrathin optoelectronics can be used to control electron flow directions during photoexcitation and open up opportunities for tandem cell assembly.

We demonstrate that by stacking WS2/ MoS2 in between graphene electrodes, photovoltaic effects are extracted from TMDs, which otherwise would not exist in their isolated states even through contact engineering with graphene electrodes.

  • Manually stacking WS2(1L) and MoS2(1L) shows no obvious photovoltaic effects individually, whereas sandwiching them together between graphene electrodes to form GrB/ WS2(1L)/MoS2(1L)/GrT, yields Isc and |Voc| reaching 140 nA and 2.7 mV.
  • photocurrent direction could be reversed by switching the stacking sequences of WS2 and MoS2

2D Photovoltaic Devices: Progress and Prospects [46][edit]

Abstract: The discovery of the new class of 2D materials has stimulated extensive research interest for fundamental studies and applied technologies. Owing to their unique electronic and optical properties, which differ from their bulk counterparts and conventional optoelectronic materials, 2D materials at the atomic scale are very attractive for future photovoltaic devices. Over the past years, their great potential for photovoltaic applications has been widely investigated by creating a variety of specific device structures. Here, the recent progress made toward the exploitation of 2D materials for high-performance photovoltaic applications is reviewed. By addressing both lateral and vertical configurations, the prospects offered by 2D materials for future generations of photovoltaic devices are elucidated. In addition, the challenges facing this rapidly progressing research field are discussed, and routes to commercially viable 2D-material-based photovoltaic devices are proposed.

  • is a good review paper on 2D PV
  • In the following sections, we divide the realization of photovoltaic devices into two different configurations, i.e., lateral and vertical structures.
  • Table I in page 13 summarize all parameters of 2D PV in Lit

Symmetry-Controlled Reversible Photovoltaic Current Flow in Ultrathin All 2D Vertically Stacked Graphene/MoS2/WS2/Graphene Devices [47][edit]

Abstract: Atomically thin vertical heterostructures are promising candidates for optoelectronic applications, especially for flexible and transparent technologies. Here, we show how ultrathin all two-dimensional vertical-stacked type-II heterostructure devices can be assembled using only materials grown by chemical vapor deposition, with graphene (Gr) as top and bottom electrodes and MoS2/WS2 as the active semiconductor layers in the middle. Furthermore, we show that the stack symmetry, which dictates the type-II directionality, is the dominant factor in controlling the photocurrent direction upon light irradiation, whereas in homobilayers, photocurrent direction cannot be easily controlled because the tunnel barrier is determined by the doping levels of the graphene, which appears fixed for top and bottom graphene layers due to their dielectric environments. Therefore, the ability to direct photovoltaic current flow is demonstrated to be only possible using heterobilayers (HBs) and not homobilayers. We study the photovoltaic effects in more than 40 devices, which allows for statistical verification of performance and comparative behavior. The photovoltage in the graphene/transition-metal dichalcogenide-heterobilayer/graphene (Gr/ TMD-HB (MoS2/WS2)/Gr) increases up to 10 times that generated in the monolayer TMD devices under the same optical illumination power, due to efficient charge transfer between WS2 and MoS2 and extraction to graphene electrodes. By applying external gate voltages (Vg), the band alignment can be tuned, which in turn controls the photovoltaic effect in the vertical heterostructures. The tunneling-assisted interlayer charge recombination also plays a significant role in modulating the photovoltaic effect in the Gr/TMD-HB/Gr. These results provide important insights into how layer symmetry in verticalstacked graphene/TMD/graphene ultrathin optoelectronics can be used to control electron flow directions during photoexcitation and open up opportunities for tandem cell assembly.

We demonstrate that by stacking WS2/ MoS2 in between graphene electrodes, photovoltaic effects are extracted from TMDs, which otherwise would not exist in their isolated states even through contact engineering with graphene electrodes.

  • Manually stacking WS2(1L) and MoS2(1L) shows no obvious photovoltaic effects individually, whereas sandwiching them together between graphene electrodes to form GrB/ WS2(1L)/MoS2(1L)/GrT, yields Isc and |Voc| reaching 140 nA and 2.7 mV.
  • photocurrent direction could be reversed by switching the stacking sequences of WS2 and MoS2

Towards efficient photon management in nanostructured solar cells: Role of 2D layered transition metal dichalcogenide semiconductors [48][edit]

Abstract: Photovoltaic devices are the source for future energy where the naturally abundant solar energy is converted into electricity using photoactive materials. An efficient photon management mechanism is essential for achieving high efficiency next generation solar cells. The use semiconducting two dimensional (2D) transition metal dichalcogenide (TMDCs) nanosheets light absorbing layer in modern solar cell is inevitable. Diverse large area synthesis tools to tailor nanosheets and its incorporation in solar cell cover the entire solar spectrum for enhanced photon management. In this review, the case to case use of TMDCs in various photovoltaic devices as an efficient absorber layer has been discussed. Experimental measures to overcome the limitations of pristine TMDC layers due to its atomic layer thickness were also reviewed. It can be seen that, the device performance of the TMDCs based solar cells is showing significant improvement in comparison with conversional silicon based photovoltaics

  • This is a Review paper with focus on TMDs
  • application in OPVs One of the most emerging fields in the photovoltaics is the organic photovoltaics (OPVs) due to flexibility, low cost, light weight and relative ease to fabricate large area. In OPVs, electron transport layer (ETL) or hole transport layer (HTL) which is placed in between the active layer and the cathode is inevitable to obtain high power convention efficiency (PCE). The role of this transport layer is to modify the work function of cathode and reduce the carrier recombination in the active layer. The exciting electronic and optical properties of layered TMDC semiconductors are now being placed as transport (e/h) layers in OPVs.


Two-dimensional materials in perovskite solar cells [49][edit]

Abstract: Organic-inorganic hybrid perovskite solar cells (PSCs) have experienced a rapid development in the pastfew years, reaching a certified efficiency over 23%. The semiconducting perovskite materials have showngreat potential for photovoltaic applications because of their outstanding optoelectronic properties.Meanwhile, two-dimensional (2D) materials have attracted increasing attention due to their exceptionalchemical, electrical and physical properties. Recently, the synergic effects due to the combination of 2Dmaterials and organic-inorganic hybrid perovskite materials have been revealed by many groups. In thisreview, recent works on the applications of 2D materials in PSCs are comprehensively presented anddiscussed. The progress and advantages of 2D materials as electrodes, charge transport layers and ad-ditives in PSCs are systemically reviewed. Finally, critical challenges and prospects of this researchfieldare addressed.

Flexible Solar Cells[edit]

Transparent Conductive Oxide-Free Graphene-Based Perovskite Solar Cells with over 17% Effi ciency [50][edit]

Abstract: Highly efficient transparent conductive oxide (TCO)‐free perovskite (CH3NH3PbI3) solar cells are demonstrated by using a graphene transparent anode and organic carrier transport materials. By adding a few nanometer‐thick MoO3 layer, wettability and work function of the graphene electrode are enhanced to enable a 17.1% power conversion efficiency, which is so far the highest efficiency for TCO‐free solar cells.


Superflexible, high-efficiency perovskite solar cells utilizing graphene electrodes: towards future foldable power sources [51][edit]

Abstract: With rapid and brilliant progress in performance over recent years, perovskite solar cells have drawn increasing attention for portable power source applications. Their advantageous features such as high efficiency, low cost, light weight and flexibility should be maximized if a robust and reliable flexible transparent electrode is offered. Here we demonstrate highly efficient and reliable super flexible perovskite solar cells using graphene as a transparent electrode. The device performance reaches 16.8% with no hysteresis comparable to that of the counterpart fabricated on a flexible indium-tin-oxide electrode showing a maximum efficiency of 17.3%. The flexible devices also demonstrate superb stability against bending deformation, maintaining >90% of its original efficiency after 1000 bending cycles and 85% even after 5000 bending cycles with a bending radius of 2 mm. This overwhelming bending stability highlights that perovskite photovoltaics with graphene electrodes can pave the way for rollable and foldable photovoltaic applications.

Visibly-Transparent Organic Solar Cells on Flexible Substrates with All-Graphene Electrodes [52][edit]

Abstract: Portable electronic devices have become increasingly widespread. Because these devices cannot always be tethered to a central grid, powering them will require low-cost energy harvesting technologies. As a response to this anticipated demand, this study demonstrates transparent organic solar cells fabricated on fl exible substrates, including plastic and paper, using graphene as both the anode and cathode. Optical transmittance of up to 69% at 550 nm is achieved by combining the highly transparent graphene electrodes with organic polymers that primarily absorb in the near-IR and near-UV regimes. To address the challenge of transferring graphene onto organic layers as the top electrode, this study develops a room temperature dry-transfer technique using ethylene-vinyl-acetate as an adhesion-promoting interlayer. The power conversion effi ciency achieved for fl exible devices with graphene anode and cathode devices is 2.8%–3.8% at for optical transmittance of 54%–61% across the visible regime. These results demonstrate the versatility of graphene in optoelectronic applications and it is important step toward developing a practical power source for distributed wireless electrical systems.

Ultrathin and flexible perovskite solar cells with graphene transparent electrodes [53][edit]

Abstract:

Flexible and light weight perovskite solar cells have attracted much attention recently for their broad potential applications especially in wearable electronics. However, highly flexible devices cannot be realized with the conventional transparent electrodes based on conductive oxides since they are rigid and brittle. Here, we demonstrate the fabrication of ultrathin and flexible perovskite solar cells with graphene transparent electrodes for the first time. The flexible devices with the structure of polyethylene terephthalate/graphene/poly(3-hexylthiophene)/CH3NH3PbI3/PC71BM/Ag are prepared on 20 mm-thick polyethylene terephthalate substrates by low-temperature solution process, which show the power conversion efficiency of 11.5% and high bending durability. Moreover, the devices demonstrate the power output per weight (specific weight) of about 5 W/g, which is much higher than those of conventional inorganic solar cells. This work paves a way for preparing flexible perovskite solar cells as well as other optoelectronic devices by using graphene transparent electrodes.

The Role of Graphene and Other 2D Materials in Solar Photovoltaics [54][edit]

Abstract: 2D materials have attracted considerable attention due to their exciting optical and electronic properties, and demonstrate immense potential for next-generation solar cells and other optoelectronic devices. With the scaling trends in photovoltaics moving toward thinner active materials, the atomically thin bodies and high flexibility of 2D materials make them the obvious choice for integration with future-generation photovoltaic technology. Not only can graphene, with its high transparency and conductivity, be used as the electrodes in solar cells, but also its ambipolar electrical transport enables it to serve as both the anode and the cathode. 2D materials beyond graphene, such as transition-metal dichalcogenides, are direct-bandgap semiconductors at the monolayer level, and they can be used as the active layer in ultrathin flexible solar cells. However, since no 2D material has been featured in the roadmap of standard photovoltaic technologies, a proper synergy is still lacking between the recently growing 2D community and the conventional solar community. A comprehensive review on the current state-of-the-art of 2D-materials-based solar photovoltaics is presented here so that the recent advances of 2D materials for solar cells can be employed for formulating the future roadmap of various photovoltaic technologies.

  • Provskite shown > 20% PCE but poor stability prevents commercialization (page 3 of 35)


Highly flexible, high-performance perovskite solar cells with adhesion promoted AuCl3-doped graphene electrodes [55][edit]

Abstract: Super flexible TCO-free FAPbI3−xBrx planar type inverted perovskite solar cells with a 17.9% power conversion efficiency under 1 sun conditions were demonstrated by introducing an APTES (3-aminopropyl triethoxysilane) adhesion promoter between a PET flexible substrate and a AuCl3-doped single-layer graphene transparent electrode (TCE). Due to the formation of covalent bonds by the APTES inter-layer, the AuCl3-GR/APTES/PET substrate had excellent flexibility, whereas the AuCl3-GR/PET substrate and the ITO/PET substrate had significant degradation of the sheet resistance after a bending test due to the break-off or delamination of AuCl3-GR from the PET substrate and the cracking of ITO. Accordingly, the perovskite solar cells constructed on the AuCl3-GR/APTES/PET TCE substrate exhibited excellent bending stability and they maintained their PCE at over 90% of the initial value after 100 bending cycles at R ≥ 4 mm




Super-flexible bis(trifluoromethanesulfonyl)-amide doped graphene transparent conductive electrodes for photo-stable perovskite solar cells [56][edit]

Abstract: Super-flexible bis(trifluoromethanesulfonyl)-amide (TFSA)-doped graphene transparent conducting electrode (GR TCE)-based FAPbI3 − xBrx perovskite solar cells with 18.9% power conversion efficiency (PCE) for a rigid device and 18.3% for a flexible one are demonstrated because the TFSA-doped GR TCE reveals high conductivity and high transmittance. The unencapsulated TFSA-doped GR TCE-based cell maintained ∼95% of its initial PCE under a continuous light soaking of 1 Sun at 60 °C/30% relative humidity for 1000 h. In addition, the TFSA-doped GR TCE-based flexible perovskite solar cells show excellent bending stabilities, maintaining PCEs of ∼85, ∼75, and ∼35% of their original values after 5000 bending cycles, at R = 12, 8, and 4 mm, respectively





Graphene[edit]

Roll-to-roll production of 30-inch graphene films for transparent electrodes [57][edit]

Abstract; The outstanding electrical1, mechanical2,3 and chemical4,5 properties of graphene make it attractive for applications in flexible electronics6,7,8. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as ∼125 Ω □−1 with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as ∼30 Ω □−1 at ∼90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.


Are There Fundamental Limitations on the Sheet Resistance and Transmittance of Thin Graphene Films? [58][edit]

Abstract From published transmittance and sheet resistance data, we have calculated a figure of merit for transparent, conducting graphene films; the DC to optical conductivity ratio, σDC/σOp. For most reported results, this conductivity ratio clusters around the values σDC/σOp = 0.7, 4.5, and 11. We show that these represent fundamental limiting values for networks of graphene flakes, undoped graphene stacks, and graphite films, respectively. The limiting value for graphene flake networks is much too low for transparent-electrode applications. For graphite, a conductivity ratio of 11 gives Rs = 377Ω/◻ for T = 90%, far short of the 10 Ω/◻ minimum requirement for transparent conductors in current driven applications. However, we suggest that substrate-induced doping can potentially increase the 2-dimensional DC conductivity enough to make graphene a viable transparent conductor. We show that four randomly stacked graphene layers can display T ≈ 90% and 10 Ω/◻ if the product of carrier density and mobility reaches nμ = 1.3 × 1017 V−1 s−1. Given achieved doping values and attainable mobilities, this is just possible, resulting in potential values of σDC/σOp of up to 330. This is high enough for any transparent conductor application.


Electrode Grids for ITO-free Organic Photovoltaic Devices [59][edit]

Abstract; Silver grids are utilized to exclude the expensive use of indium tin oxide (ITO) in conjugated polymer photovoltaic devices. The grids are generated by electroless deposition from elastomeric microfluidic channels onto transparent substrates. The organic photovoltaic devices demonstrated here, with minimized series resistance, are confirmed to have characteristics comparable to devices exploiting ITO


Bending Fatigue Study of Sputtered ITO on Flexible Substrate [60][edit]

Abstract; Recently, there has been a tremendous rise in production of portable electronic devices. To produce flexible devices, flexible substrates should replace conventional glass substrates. Indium-tin-oxide (ITO) is the preferred transparent conducting layer used in the display technology. Although ITO has excellent sheet resistance and very good optical properties, ITO can crack at very low tensile strains which might cause failure in the conductive layer because of the unusual structure of a very thin film of brittle ceramic material applied to a polymer substrate. Therefore, the mechanics of ITO on flexible substrates has been thoroughly considered in the design and manufacturing of flexible devices. In a typical roll-to-roll manufacturing process, many challenges exist during the travel of the coated web over the rollers which produce bending stresses that might cause failure even if the stresses are below the yield strength of the material. Therefore, the high cycle bending fatigue of ITO thin films on flexible substrates is of a significant importance. In this work, high cycle bending fatigue experiments were conducted on ITO coated PET substrate. The effect of bending diameter, bending frequency, and sample width on the change in electrical resistance was investigated. High magnification images were obtained to observe crack initiation and propagating in the ITO layer. The goal of this work is to establish a baseline for a comprehensive reliability study of ITO thin films on flexible substrate. It was found that bending diameters as well as the number of bending cycles have a great influence on the electrical conductivity of the ITO layer.

Scale up perovskite solar cells (PSCs)[edit]

Upscaling of Perovskite Solar Cells: Fully Ambient Roll Processing of Flexible Perovskite Solar Cells with Printed Back Electrodes [61][edit]

Abstract: A scaling effort on perovskite solar cells is presented where the device manufacture is progressed onto flexible substrates using scalable techniques such as slot‐die roll coating under ambient conditions. The printing of the back electrode using both carbon and silver is essential to the scaling effort. Both normal and inverted device geometries are explored and it is found that the formation of the correct morphology for the perovskite layer depends heavily on the surface upon which it is coated and this has significant implications for manufacture. The time it takes to form the desired layer morphology falls in the range of 5–45 min depending on the perovskite precursor, where the former timescale is compatible with mass production and the latter is best suited for laboratory work. A significant loss in solar cell performance of around 50% is found when progressing to using a fully scalable fabrication process, which is comparable to what is observed for other printable solar cell technologies such as polymer solar cells. The power conversion efficiency (PCE) for devices processed using spin coating on indium tin oxide (ITO)‐glass with evaporated back electrode yields a PCE of 9.4%. The same device type and active area realized using slot‐die coating on flexible ITO‐polyethyleneterphthalate (PET) with a printed back electrode gives a PCE of 4.9%.

  • Introducing other methods mostly used instead of spin coating


Perovskite SolarCells: Fromthe Laboratorytothe Assembly Line [62][edit]

Abstract: Despite the fact that perovskite solar cells (PSCs) have a strong potential as a next‐generation photovoltaic technology due to continuous efficiency improvements and the tunable properties, some important obstacles remain before industrialization is feasible. For example, the selection of low‐cost or easy‐to‐prepare materials is essential for back‐contacts and hole‐transporting layers. Likewise, the choice of conductive substrates, the identification of large‐scale manufacturing techniques as well as the development of appropriate aging protocols are key objectives currently under investigation by the international scientific community. This Review analyses the above aspects and highlights the critical points that currently limit the industrial production of PSCs and what strategies are emerging to make these solar cells the leaders in the photovoltaic field.

  • a good review paper on scale up perovskite solar cells


Toward Industrial-Scale Production of Perovskite Solar Cells: Screen Printing, Slot-Die Coating, and Emerging Techniques [63][edit]

Abstract: Perovskite solar cells (PSCs) have attracted intensive attention of the researchers and industry due to their high efficiency, low material cost, and simple solution-based fabrication process. Along with the development of device configurations, materials, and fabrication techniques, the efficiency has rapidly increased from the initial 3.8 to recent 22.7%. However, fundamental studies on PSCs are usually yielded through lab-scale procedures and carried out on small-area (≤1 cm2) devices. Recently, various deposition methods, such as screen printing, slot-die coating, soft-cover coating, spraying coating, etc., have been developed to enlarge the device area from the millimeters to hundreds of centimeters scale. Herein, we discuss the advances of up-scaling of PSCs and outline the fabrication methods from lab-scale to industrial-scale. Screen printing and slot-die coating have been regarded as the most promising methods toward the mass production of PSCs, and more emerging techniques are also anticipated in this enterprise.


Outlook and Challenges of Perovskite Solar Cells toward Terawatt-Scale Photovoltaic Module Technology [64][edit]

Abstract: Perovskite solar cells based on organic-inorganic hybrid perovskites have emerged as a low-cost and high-efficiency thin-film photovoltaic (PV) technology that holds the potential to compete in the PV market. Developing scalable processes with solution deposition (e.g., blade, slot die, and spray coating) enables continuous roll-to-roll or sheet-to-sheet processing with flexible or rigid substrates that can be used for future terawatt-scale production of perovskite solar modules. Scaling up from laboratory-scale device fabrication based on spin coating to scalable deposition suitable for an industry setting generally requires re-evaluation/re-design of many factors associated with device fabrication and characterization. Here, we provide our perspective regarding large-scale manufacturing and deployment of perovskite PV technology. We discuss challenges in three key areas: (1) a scalable process for large-area perovskite module fabrication; (2) less hazardous chemical routes for perovskite solar cell fabrication; and (3) suitable perovskite module designs for different applications. Advances along these key areas are crucial to the success of perovskite PV technology in the future

  • I received the article full text through ILLiad MTU library

Applications of Flexible PVs[edit]

A PCBM-assisted perovskite growth process to fabricate high efficiency semitransparent solar cells [65][edit]

Abstract: Developing highly efficient perovskite solar cells in a simple and rapid fashion will open the window for their potential commercialization. Semi-transparent devices are of great interest due to their attractive application in building integrated photovoltaics (BIPVs). In this study, efficient perovskite solar cells with good transparency in the visible wavelength range have been developed by a facile and low-temperature PCBM-assisted perovskite growth method. This method results in the formation of a perovskite-PCBM hybrid material at the grain boundaries which is observed by EELS mapping and confirmed by steady-state photoluminescence (PL) spectroscopy, transient photocurrent (TP) measurements and X-ray photoelectron spectroscopy (XPS). The PCBM-assisted perovskite growth method involves fewer steps and therefore is less expensive and time consuming than other similar methods. The semitransparent solar cells developed using this method exhibited power conversion efficiency (PCE) ranging from 12% to 4% depending on the average visible transmittance (AVT) ranging from 3% to 35%. The as-fabricated semitransparent perovskite solar cell with an active layer thickness of only about 150 nm, which is only less than half the active layer thickness of a typical perovskite solar cell, provided a PCE as high as 9.1% with an AVT of 18% and more than 12% with an AVT of 3%.

System Analysis[edit]

Cost-Performance Analysis of Perovskite Solar Modules [66][edit]

Abstract: Perovskite solar cells (PSCs) are promising candidates for the next genera-tion of solar cells because they are easy to fabricate and have high power conversion efficiencies. However, there has been no detailed analysis of the cost of PSC modules. We selected two representative examples of PSCs and performed a cost analysis of their productions: one was a moderate-efficiency module produced from cheap materials, and the other was a high-efficiency module produced from expensive materials. The costs of both modules were found to be lower than those of other photovoltaic technologies. We used the calculated module costs to estimate the levelized cost of electricity (LCOE) of PSCs. The LCOE was calculated to be 3.5–4.9 US cents/kWh with an efficiency and lifetime of greater than 12% and 15 years respectively, below the cost of traditional energy sources



An Analysis of the Cost and Performance of Photovoltaic Systems as a Function of Module Area [67][edit]

  • this is a detailed analysis by NREL can be a good reference for some parameters assumptions


Building-Integrated Photovoltaics (BIPV) in the Residential Sector: An Analysis of Installed Rooftop System Prices [68][edit]

  • this NREL analysis is good for rooftop case

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