(/* Enhanced photon absorption in spiral nanostructured solar cells using layered 2D materials Tahersima, Mohammad H., and Volker J. Sorger. "Enhanced photon absorption in spiral nanostructured solar cells using layered 2D materials." Nanotechnology 26,...)
(/* Graphene coupled with Pt cubic nanoparticles for high performance, air-stable graphene-silicon solar cells Huang, Kun, Yucong Yan, Xuegong Yu, Hui Zhang, and Deren Yang. "Graphene coupled with Pt cubic nanoparticles for high performance, air-stable...)
Line 325: Line 325:
*Adding TiO2 antireflective film enhance PCE to 10%
*Adding TiO2 antireflective film enhance PCE to 10%
* this can be called as 0, 2 and 3 dimensional structure
* this can be called as 0, 2 and 3 dimensional structure
===[https://onlinelibrary.wiley.com/doi/epdf/10.1002/adma.201701168 Single Atomically Sharp Lateral Monolayer p-n Heterojunction Solar Cells with Extraordinarily High  Power Conversion Efficiency <ref>Tsai, Meng‐Lin, Ming‐Yang Li, José Ramón Durán Retamal, Kai‐Tak Lam, Yung‐Chang Lin, Kazu Suenaga, Lih‐Juann Chen, Gengchiau Liang, Lain‐Jong Li, and Jr‐Hau He. "Single Atomically Sharp Lateral Monolayer p‐n Heterojunction Solar Cells with Extraordinarily High Power Conversion Efficiency." Advanced Materials 29, no. 32 (2017): 1701168.</ref>]===
'''Abstract:'''


===[https://www.sciencedirect.com/science/article/pii/S0038092X17310599/pdfft?md5=080e854469ee4535f86da08efa0ddf4c&pid=1-s2.0-S0038092X17310599-main.pdf High efficiency graphene/MoS2/Si Schottky barrier solar cells using layer-controlled MoS2 films <ref>Ma, Jun, He Bai, Wei Zhao, Yujie Yuan, and Kailiang Zhang. "High efficiency graphene/MoS 2/Si Schottky barrier solar cells using layer-controlled MoS 2 films." Solar Energy 160 (2018): 76-84.</ref>]===
===[https://www.sciencedirect.com/science/article/pii/S0038092X17310599/pdfft?md5=080e854469ee4535f86da08efa0ddf4c&pid=1-s2.0-S0038092X17310599-main.pdf High efficiency graphene/MoS2/Si Schottky barrier solar cells using layer-controlled MoS2 films <ref>Ma, Jun, He Bai, Wei Zhao, Yujie Yuan, and Kailiang Zhang. "High efficiency graphene/MoS 2/Si Schottky barrier solar cells using layer-controlled MoS 2 films." Solar Energy 160 (2018): 76-84.</ref>]===

Revision as of 19:54, 10 February 2019


Note

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

Electric Field Effect in Atomically Thin Carbon Films [1]

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

Literature Review

The reflectivity spectra of some group VA transition metal dichalcogenides [2]

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 [3]

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 [4]

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 [5]

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 [6]

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 [7]

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 [8]

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 [9]

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 [10]

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 [11]

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 [12]

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 [13]

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 [14]

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 [15]

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 [16]

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 [17]

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 [18]

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 [19]

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 [20]

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 [21]

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 [22]

Abstract:

Role of Interfacial Oxide in High-Efficiency Graphene–Silicon Schottky Barrier Solar Cells [23]

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 [24]

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 [25]

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 [26]

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

  • 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 [27]

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 [28]

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 [29]

Abstract:

Combined effect of double antireflection coating and reversible molecular doping on performance of few-layer graphene/n-silicon Schottky barrier solar cells [30]

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 [31]

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 [32]

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 [33]

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 [34]

Abstract:

Mixed-dimensional van der Waals heterostructures [35]

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 [36]

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 [37]

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 [38]

Abstract:

High efficiency graphene/MoS2/Si Schottky barrier solar cells using layer-controlled MoS2 films [39]

Abstract: Graphene/MoS2/Si Schottky barrier solar cell is investigated

  • 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 [40]

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 [41]

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%


Symmetry-Controlled Reversible Photovoltaic Current Flow in Ultrathin All 2D Vertically Stacked Graphene/MoS2/WS2/Graphene Devices [42]

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 [43]

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.

Symmetry-Controlled Reversible Photovoltaic Current Flow in Ultrathin All 2D Vertically Stacked Graphene/MoS2/WS2/Graphene Devices [44]

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 [45]

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.

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