HYDROGEN COLLISION MODEL OF LIGHT-INDUCED METASTABILITY IN HYDROGENATED AMORPHOUS SILICON 1997[edit | edit source]
- New model for SWE in undoped a-Si:H: When mobile H atoms generated by excess carriers collide, they form metastable, immobile complexes containing two Si-H bonds. The metastable defects of the SW effect are left behind on the sites from which the colliding H were excited.
- goes through the model and explains the model's assumptions such as constants. excitation rate of mobile H per unit volume isR, = kHNHG,
- "The model predicts an early-time rise of N,, a latency time for metastable DB creation and a decay of Ndb due to mobile H retrapping after the incident light is extinguished."
Howard M. Branz. HYDROGEN COLLISION MODEL OF LIGHT-INDUCED METASTABILITY IN HYDROGENATED AMORPHOUS SILICON. Solid State Communications.V ol. 105. No. 6. pp. 387-391. 1998
Microscopic nature of Staebler-Wronski defect formation in amorphous silicon 1997[edit | edit source]
Abstract: Light-induced metastable defects in a-Si:H are proposed to be silicon dangling bonds accompanied by pairs of hydrogen atoms breaking a silicon bond, forming a complex with two Si-H bonds. This supports the model of Branz. These defects are the analog of the H2* defect in c-Si and their energy correlates with the bond-angle strain. Several features of the annealing are well described by this defect complex.
R. Biswas and B. C. Pan. Microscopic nature of Staebler-Wronski defect formation in amorphous silicon. Appl. Phys. Lett. 72 (3), 19 January 1998
Evidence for proton motion in the recovery of light-induced degradation in amorphous silicon solar cells 1997[edit | edit source]
- "The dependence of the recovery rate on field strength, temperature and light intensity can be explained by a model based on the local motion of a proton within a metastable complex."
- hydrogen not near light induced dangle bonds from ESR, therefore long range motion of hydrogen might cause metastable centers
D. E. Carlson and K. Rajan. Evidence for proton motion in the recovery of light-induced degradation in amorphous silicon solar cells. J. Appl. Phys. 83 (3), 1 February 1998
Differences in the densities of charged defect states and kinetics of Staebler–Wronski effect in undoped (nonintrinsic) hydrogenated amorphous silicon thin films 1997[edit | edit source]
Abstract: A variety of undoped (nonintrinsic) hydrogenated amorphous silicon (a-Si:H) thin films was studied in greater detail using steady-state photoconductivity, σph, subband-gap absorption, α(hν), steady-state photocarrier grating (SSPG), and electron-spin-resonance (ESR) techniques both in the annealed and stabilized light soaked states. The experimental results were self-consistently modeled using a detailed numerical analysis. It was found that large differences in the optoelectronic properties of device quality a-Si:H thin films can only be explained using a gap state distribution which consists of positively charged D+ defect states above the Fermi level, the neutral D0 defect states, and the negatively charged D- defect states below the Fermi level. There are large differences both in the densities of neutral and charged defect states and R ratios in different a-Si:H films in the annealed state. The densities of both neutral and charged defect states increased, however, R ratios decreased in the stabilized light soaked state. Very good agreement was obtained between the densities of neutral defect states measured by ESR and those derived from the numerical analysis in the stabilized light soaked state. The kinetics of the Staebler–Wronski effect was also investigated. There was no direct correlation between the decrease of steady-state photoconductivity and increase of subband-gap absorption. The self-consistent fits to wide range of experimental results obtained with the three Gaussian distributions of charged defect states imply that this model is much better representation of the bulk defect states in undoped hydrogenated amorphous silicon thin films.
Gunes, Mehmet; Wronski, Christopher R.;, "Differences in the densities of charged defect states and kinetics of Staebler–Wronski effect in undoped (nonintrinsic) hydrogenated amorphous silicon thin films," Journal of Applied Physics, vol.81, no.8, pp.3526-3536, Apr 1997 doi: 10.1063/1.365000
Structural disorder induced in hydrogenated amorphous silicon by light soaking 1998[edit | edit source]
Abstract: We show, using variable coherence transmission electron microscopy, that light soaking of amorphous hydrogenated silicon thin films leads to structural changes. We speculate that the structural changes are associated with instability in the as-deposited material. We suggest that improved immunity to Staebler–Wronski degradation could be achieved by a less-ordered material which is closer to the ideal continuous random network.
J. M. Gibson, M. M. J. Treacy, P. M. Voyles, H-C. Jin and J. R. Abelson.Structural disorder induced in hydrogenated amorphous silicon by light soaking. APPLIED PHYSICS LETTERS, VOLUME 73, NUMBER 21. 23 NOVEMBER 1998.
Potential of amorphous silicon for solar cells 1999[edit | edit source]
Abstract: This paper reviews recent developments in the field of amorphous-silicon-based thin-film solar cells and discusses potentials for further improvements. Creative efforts in materials research, device physics, and process engineering have led to highly efficient solar cells based on amorphous hydrogenated silicon. Sophisticated multijunction solar cell designs make use of its unique material properties and strongly suppress light induced degradation. Texture-etching of sputtered ZnO:Al films is presented as a novel technique to design optimized light trapping schemes for silicon thin film solar cells in both p-i-n and n-i-p device structure. Necessary efforts will be discussed to close the efficiency gap between the highest stabilized efficiencies demonstrated on lab scale and efficiencies achieved in production. In case of a-Si:H=a-Si:H stacked cells prepared on glass substrates, significant reduction of process-related losses and the development of superior TCO substrates on large areas promise distinctly higher module efficiencies. A discussion of future perspectives comprises the potential of new deposition techniques and concepts combining the advantages of amorphous and crystalline silicon thin-film solar cells.
B. Rech, H. Wagner. Potential of amorphous silicon for solar cells. Appl. Phys. A 69, 155–167 (1999) / Digital Object Identifier (DOI) 10.1007/s003399900064
Light-induced structural changes and their correlation to metastable defect creation in intrinsic hydrogenated amorphous silicon films 2000[edit | edit source]
Abstract: Device-quality intrinsic a-Si:H films were prepared by three methods, hot-wire (HW) chemical vapor deposition (CVD), and glow-discharge (GD) CVD with and without H dilution, and show varied light-induced metastable defect creation [Staebler-Wronski effect (SWE)]. We found the following: ~a! In addition to the nonuniform H distribution, the a-Si network is inhomogeneous, and the film prepared by GD is more homogeneous than the HW film. ~b! The light-induced increase of Si-H stretching absorption at ;2000 cm21 is on the order of 1022 in all the films, and an additional decrease at ;2025 cm21 is found in films with larger SWE. ~c! The change of the compressive stress is on the order of 1024 of the initial value in the HW films, which is the same order of magnitude as in GD films. Both the initial stress and light-induced volume expansion decrease with decreasing Si-H concentration. No simple correlation between the light-induced structural changes and the conductivity changes was found in the HW a-Si:H films. We describe the light-induced structural changes in conjunction with the creation of metastable defects by a two-phase model.
Daxing Han, Jonathan Baugh, and Guozhen Yue. Light-induced structural changes and their correlation to metastable defect creation in intrinsic hydrogenated amorphous silicon films. PHYSICAL REVIEW B, VOLUME 62, NUMBER 11. 15 SEPTEMBER 2000-I
Annealing and recrystallization of hydrogenated amorphous silicon 2001[edit | edit source]
This paper uses positron annihilation and x-ray diffraction to determine microvoids and microcrystalline phase. This paper annealed the cells at 400 C and saw recrystallization and low concentration of microvoids which were not there before annealing.
D. T. Britton, A. Hempel, and M. Ha¨rting,G. Ko¨gel, P. Sperr, and W. Triftsha¨user,C. Arendse and D. Knoesen. Annealing and recrystallization of hydrogenated amorphous silicon. PHYSICAL REVIEW B, VOLUME 64, 075403.
Temperature dependence of the optically induced production and annealing of silicon dangling bonds in hydrogenated amorphous silicon 2002[edit | edit source]
Abstract: In hydrogenated amorphous silicon the kinetics of the optically induced production and thermal annealing of silicon dangling bonds have been measured at temperatures between 25 and 480 K using electron spin resonance ~ESR!. Below about 150 K the measurement of optically induced silicon dangling bonds is masked by long-lived, band-tail carriers that accumulate with time t as t1/3. It is known that these long-lived carriers can be quenched by infrared light. However, optically, it is not possible to completely remove them. The production rate for optically induced silicon dangling bonds decreases with decreasing temperature. Below about 100 K degradation is at most half as efficient as at room temperature and is nearly temperature independent below approximately 100 K. Additionally, defects created by 10 h of irradiation below 100 K almost entirely anneal at T>300 K. It is common procedure to anneal a-Si:H samples for 30 min at 175 °C to restore the as-deposited defect density. However, by repeatedly performing degradation and annealing cycles we find that a small fraction of defects is not restored by annealing at 175 °C and that these defects slowly accumulate with degradation. For defects created at all temperatures we find the same ESR fingerprint, indicating that only one dominant type of defect is created, presumably the silicon dangling bond, and we conclude that different, temperature-dependent stabilization processes must exist. These results lead to new constraints for models that attempt to explain the Staebler-Wronski effect.
N. A. Schultz and P. C. Taylor. Temperature dependence of the optically induced production and annealing of silicon dangling bonds in hydrogenated amorphous silicon. PHYSICAL REVIEW B, VOLUME 65, 235207
Experimental and Computer Modelling Studies of Metastability of Amorphous Silicon Based Solar Cells. 2003 THESIS [ASA][edit | edit source]
This thesis discusses the properties of a-Si:H and then the metastable properties. The experiments that were completed were photodegradation, the effect of thickness, buffer layer effects, intrinsic layer made from deuterium and transport props during light soaking. The paper then modeled the cells using ASA and modelling the degradation kinetics.
Geoffrey Munyeme. Experimental and Computer Modelling Studies of Metastability of Amorphous Silicon Based Solar Cells. 2003. ISBN 90-393-3310-6. Technische Universiteit Delft
Light-induced defect states in hydrogenated amorphous silicon centered around 1.0 and 1.2 eV from the conduction band edge 2003[edit | edit source]
This paper uses 1 micrometer cells and degrades the cells at 25 and 75 with R=0, 10. The paper looks at the electron mobility and subgap absorption.
"No conclusions are drawn here about the defects associated with these states; however, their distinct differences in their creation kinetics cannot be overlooked in the attempts on establishing the origin of the Staebler–Wronski effect"
J. M. Pearce, J. Deng, R. W. Collins, and C. R. Wronski. Light-induced defect states in hydrogenated amorphous silicon centered around 1.0 and 1.2 eV from the conduction band edge. Appl. Phys. Lett., Vol. 83, No. 18, 3 November 2003
Light-induced recovery of a-Si solar cells 2003[edit | edit source]
Abstract: The light-induced recovery in efficiency of amorphous silicon (a-Si) solar cells has been studied. The recovery of solar cells degraded by a concentrated light-soaking was accelerated under 1 sun illumination as compared with that in the dark. A similar phenomenon has been observed under current injection. The kinetics of light-induced annealing has been discussed on the basis of a series of the experiments.
S. Fujikake, H. Ota, M. Ohsawa, T. Hama, Y. Ichikawa and H. Sakai. Light-induced recovery of a-Si solar cells. Solar Energy Materials and Solar Cells. Volume 34, Issues 1-4, 1 September 1994, Pages 449-454
Performance analysis of a-Si:H p–i–n solar cells with and without a buffer layer at the p/i interface 2004[edit | edit source]
Abstract: Light soaking experiments have been conducted on a-Si:H p-i-n solar cells with a silicon carbide buffer layer at the p/i interface. The rate of light induced degradation in the performance of these solar cells is higher in the initial stages of light soaking and assumes the same levels as the cells without a buffer layer with prolonged light soaking. Computer modelling has revealed that a graded band gap buffer layer at the p/i interface containing a slightly acceptor doped defective layer next to the p-layer improves the initial performance of a-Si:H p-i-n solar cells. The modelling also reveals that the effect of the buffer layer on solar cell performance depends critically on the configuration and composition of the buffer layer.
G. Munyeme, M. Zeman, R. E. I. Schropp and W. F. van der Weg. Performance analysis of a-Si:H p–i–n solar cells with and without a buffer layer at the p/i interface. phys. stat. sol. (c) 1, No. 9, 2298–2303 (2004) / DOI 10.1002/pssc.200404853
Modeling of light-induced degradation of amorphous silicon solar cells 2007[edit | edit source]
Abstract: Light-induced degradation of hydrogenated amorphous silicon (a-Si:H) solar cells has been modeled using computer simulations. In the computer model, the creation of light-induced defects as a function of position in the solar cell was calculated using the recombination profile. In this way, a new defect profile in the solar cell was obtained and the performance was calculated again. The results of computer simulations were compared to experimental results obtained on a-Si:H solar cell with different intrinsic layer thickness. These experimental solar cells were degraded under both open- and short-circuit conditions, because the recombination profile in the solar cells could then be altered significantly. A reasonable match was obtained between the experimental and simulation results if only the mid-gap defect density was increased. To our knowledge, it is the first time that light-induced degradation of the performance and the quantum efficiency of a thickness series of a-Si:H solar cells has been modeled at once using computer simulations.
This is a VERY good paper. It uses lasers for the light degradation but it uses 150, 300, 450, 600 and 900 nm thickness at the temperature was around 35 C. The paper also models the degradation. The program was ASA (amorphous silicon analysis).
A. Klaver, R.A.C.M.M. van Swaaij. Modeling of light-induced degradation of amorphous silicon solar cells. Solar Energy Materials & Solar Cells 92 (2008) 50–60
The Effect of Illumination on Dark Conductivity and Photoconductivity of Hydrogenated Amorphous Silicon Layered Films 2009[edit | edit source]
Abstract: It is established that both the amplitude and temperature dependence of dark conductivity and photoconductivity of preilluminated high sensitivity layered films of amorphous hydrogenated silicon (a-Si:H) prepared by cyclic deposition with layer by layer annealing in hydrogen plasma depend on illumination temperature. The relaxation kinetics of the dark conductivity of these films after illumination is shut off is found to be nonmonotonic. The observed effects can be explained by fast and slow changes in the distribution of energy state density below the midgap during and after illumination.
- The studied layered a-Si:H films are characterized by high photosensitivity: ≈ 2 × 107 at T = 300 K
and white light intensity of 100 mW/cm2.
- Both the amplitude and temperature dependence of photoconductivity and the dark conductivity
of the films subjected to isochronous preliminary illumination depend on film temperature during isochronous illumination. The smallest change of room temperature photoconductivity was found for the films that were preilluminated at a temperature above room temperature.
- The observed metastable photoinduced changes
of temperature dependences of photoconductivity and dark conductivity and nonmonotonic relaxation kinetics of dark conductivity in the studied layered films after preillumination shutoff can be explained by fast and slow changes in the electronic state density distribution within the bandgap during and after illumination.
- The rapid decrease of photoconductivity and
dark conductivity during illumination and their increase after illumination shutoff may be related to the creation and relaxation of photoinduced metastable broken silicon bonds with energy levels lying below the midgap, respectively.
- The increase of dark conductivity and photocon
ductivity in the illuminated films at high temperatures can be explained by an illumination induced slow decrease of the concentration of the electronic states lying below the midgap and related to the presence of oxygen in the studied layered films.
I. A. Kurova and N. N. Ormont. The Effect of Illumination on Dark Conductivity and Photoconductivity of Hydrogenated Amorphous Silicon Layered Films. ISSN 0027-1349, Moscow University Physics Bulletin, 2009, Vol. 64, No. 5, pp. 527–531. © Allerton Press, Inc., 2009.
RECOVERY BEHAVIOR IN AMORPHOUS SILICON SOLAR MODULE AT LOW TEMPERATURE 2009[edit | edit source]
The modules were annealed at 25,35,45,55,65C using a flat heater. It was found that at higher temperatures, the module had a higher FF.
978-1-4244-2950-9/09 IEEE Hsin-Hsin Hsieh, Jung-Sheng Cheng. Photovoltaics Technology Center Industrial Technology Research Institute, Hsinchu, Taiwan Corresponding author: Jung-Sheng Cheng(rscheng@itrLorg.tw)
Degradation and annealing of amorphous silicon solar cells by current injection experiment and modeling 2009[edit | edit source]
Abstract: In this paper we report in detail on the e!ect of current injection in amorphous silicon solar cells. A set of devices has been degraded and then annealed at dilerent current intensities. Device performances during the whole experiment have been monitored by current}voltage characteristics and quantum e$ciency curves. It has been found that annealing rate increases with current intensity, while stabilized photovoltaic parameters decrease. Time evolution of e$ciency and short-circuit current during degradation has been reproduced by a numerical device modeling, resulting in a pronounced increase of defects near the p-i interface. The model also demonstrated that annealing results are not well reproduced if current-induced annealing is not energy selective.
Does an annealling at 90 with open circuit, 50 and 400 mA/cm^2. Also talks about modelling. The cells decreased in eff by 46% and the Isc by 33%. Also shows the QE overtime and that the response decreases over time. Discusses how to model annealing.
Domenico Caputo. Degradation and annealing of amorphous silicon solar cells by current injection experiment and modeling. Solar Energy Materials & Solar Cells 59 (1999) 289-298
Amorphous Silicon Panel Degradation Tests[edit | edit source]
Seasonal variations in amorphous silicon solar module outputs and thin film characteristics 1993[edit | edit source]
This paper analysis the output of amorphous silicon for both summer and winter conditions and compares it to c-Si. It found that a-Si:H works best in the summer. Hence, demonstrating that a-Si:H sort of likes being hot...
R. Riither, J. Livingstone. Seasonal variations in amorphous silicon solar module outputs and thin film characteristics. Solar Energy Materials and Solar Cells 36 (1994) 29-43
Model for Staebler-Wronski Degradation Deduced from Long-Term, Controlled Light-Soaking Experiments 1996[edit | edit source]
Abstract: Long-term light-soaking experiments of amorphous silicon photovoltaic modules have now established that stabilization of the degradation occurs at levels that depend significantly on the operating conditions, as well as on the operating history of the modules. We suggest that stabilization occurs because of the introduction of degradation mechanisms with different time constants and annealing activation energies, depending on the exposure conditions. Stabilization will occur once a sufficient accumulation of different degradation mechanisms occurs. We find that operating module temperature during light-soaking is the most important parameter for determining stabilized performance. Next in importance is the exposure history of the device. The precise value of the light intensity seems least important in determining the stabilized efficiency, as long as its level is a significant fraction of 1-sun.
Bolko von Roedern and Joseph A. del Cueto. Model for Staebler-Wronski Degradation Deduced from Long-Term, Controlled Light-Soaking Experiments. NREL.
Clear separation of seasonal effects on the performance of amorphous silicon solar modules by outdoor I/V-measurements 1998[edit | edit source]
The paper first states that amorphous silicon performs better in the summer due to the better spectrum of light and that although heat lowers the eff, it might also anneal the cell to allow higher performance in the cell. Shows the four seasonal effects on the cells. 12.5% higher in the summer compared to the winter.
operating temperature in winter 60 C and summer 80 C.
Good ref for thesis.
J. Merten, J. Andreu.Clear separation of seasonal effects on the performance of amorphous silicon solar modules by outdoor I/V-measurements. Solar Energy Materials and Solar Cells 52 (1998) 11-25
J. Merten, J. Andreu/Solar Energy Materials and Solar Cells 52 (1998) 11Ð25
Improved Equivalent Circuit and Analytical Model for Amorphous Silicon Solar Cells and Modules 1998[edit | edit source]
- to show empirically that the equivalent circuit in Fig. 1 describes quite precisely the experimentally measured electrical behavior of illuminated solar cells and is able to do so for illumination levels varying over six orders of magnitude;
- to present an experimental method that can be used to determine systematically the elements of this equivalent circuit, including the new recombination loss term
- to provide a link between the equivalent circuit of Fig. 1, especially between the newly introduced recombination loss term, and theoretical treatments of recombination in amorphous silicon cells, such as
- and to illustrate the use of the new, complete equivalent circuit to investigate the long-term behavior of a commercial module during outdoor exposition
Adds recombination into idiode eqns.
J. Merten, J. M. Asensi, C. Voz, A. V. Shah, R. Platz, and J. Andreu. Improved Equivalent Circuit and Analytical Model for Amorphous Silicon Solar Cells and Modules IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 45, NO. 2, FEBRUARY 1998
Characterization of degradation in thin-film photovoltaic module performance parameters 2002[edit | edit source]
Abstract: This paper characterizes and compares the degradation observed in thin-film module performance. Three commercially available thin-film modules comprising a-Si:H, a-Si:H/a- SiGe:H/a-SiGe:H and CuInSe2 technologies were used in this study. After an initial indoor assessment the modules were deployed outdoors and periodically taken down for indoor assessment. Results obtained indicate that the a-Si modules degraded by the classical Staebler–Wronski effect. The CuInSe2 module, though known to have long-term performance stability, also degraded in this study. The CuInSe2 module showed shunting behaviour before outdoor exposure. This shunting behaviour was enhanced when the module was deployed outdoors under open-circuit conditions. A comparison of the modules' performances outdoors indicates that the low bandgap CuInSe2 material performs best at high air mass values. This paper emphasizes the importance of being able to analyze module degradation.
E.L. Meyer, E.E. van Dyk. Characterization of degradation in thin-film photovoltaic module performance parameters. Renewable Energy 28 (2003) 1455–1469
DEVELOPMENT OF PROCEDURES FOR PERFORMANCE MEASUREMENTS AND LIFETIME TESTING OF THIN FILM PHOTOVOLTAIC DEVICES 2002 [Thesis][edit | edit source]
This thesis analyses the IEC, UL, ASTM standards and discusses them in great detail.
Solveig Roschier. DEVELOPMENT OF PROCEDURES FOR PERFORMANCE MEASUREMENTS AND LIFETIME TESTING OF THIN FILM PHOTOVOLTAIC DEVICES. TKK-F-A811
Laboratory of Advanced Energy Systems Department of Engineering Physics and Mathematics Helsinki University of Technology FIN-02015 HUT, Finland
The Effect of Cell Thickness on Energy Production of Amorphous Silicon Solar Cells 2005[edit | edit source]
Abstract: Solar cells are currently evaluated under laboratory conditions and not under realistic operating conditions. Amorphous silicon (a-Si) devices exhibit a complicated dependence on operating conditions, with a major concern being the degradation of these devices in realistic operation. Optimising these devices for energy production of the stabilised state is dependent on many factors, with one of the main inputs being the overall thickness of the cell. In this paper, the effect of intrinsic layer (i-layer) thickness on the cell performance, the degradation and also the energy production under realistic conditions are investigated. It is apparent from the experiment that there has to be an optimisation of the i-layer thickness to maximise the light absorption and minimise the degradation, if higher performance and energy production is to be achieved.
This paper compares 4 normalized thickness in outdoor conditions. We do not know the temperatures or the outdoor weather conditions (jun-feb) or the exact thickness of the cells. However, this paper explains the amorphous silicon degradation issues quite well.
The results show that the thicker cell does not perform as well as the thinner cells. However the 1.3 rel was better than the 1 rel in terms of degradation... This might suggest an optimal thickness...
P. Vorasayan*, T.R. Betts, R. Gottschalg, D.G. Infield, A.N. Tiwari. Centre for Renewable Energy Systems Technology, Department of Electronic and Electrical Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK
RECOVERY OF LIGHT INDUCED DEGRADATION IN AMORPHOUS SILICON SOLAR CELLS AND MODULES 2006[edit | edit source]
This paper looks at annealing a triple junction cell from 70-110C and it was found that annealing at lower temperatures takes longer but want is more interesting is the problems associated with annealing a module over just a cell. The biggest issue is the temperature uniformity where the sides were 10 C lower and the differences was about 20%.
K. Luczak¹ C. P. Lund² P.J. Jennings¹ and J.C.L. Cornish¹ ¹Physics, Energy Studies and Nanotechnology, Murdoch University, Murdoch, Perth WA 6150 Australia ²Centre for Cleaner Production, Curtin University of Technology, GPO Box U 1987 Perth WA 6845 Australia Correspondence: Kazimierz Luczak Division of Science and Engineering Murdoch University Murdoch WA 6150 Australia E-mail: K.Luczak@murdoch.edu.au Tel.: +61 8 93606505 Fax: +61 8 93101711
Innovative Characterization of Amorphous and Thin-Film Silicon for Improved Module Performance 2008[edit | edit source]
This report discusses in depth on the material properties and how to grow a-Si:H.
Innovative Characterization of Amorphous and Thin-Film Silicon for Improved Module Performance 1 February 2005 – 31 July 2008 P.C. Taylor and G.A. Williams University of Utah Salt Lake City, Utah NREL Subcontract Report NREL/SR-520-46649 September 2009
ANALYSIS OF ANNEALING AND DEGRADATION EFFECTS ON A-SI PV MODULES 2008[edit | edit source]
Abstract: The interest to thoroughly investigate the characteristics of the annealing and degradation processes comes from the encouraging results obtained with a thermally isolated a-Si PV plant . Findings showed that the better thermal behaviour and annealing processes of a-Si compared to c-Si technologies compensated for significant part of losses due to the nearly horizontal roof integration. Therefore this project aims to deeply investigate on degradation – due to sunlight (Staebler-Wronski effect) – and annealing of a-Si at different temperatures and under real outdoor operating conditions. So far an analysis on four a-Si triple junction PV modules has been carried out. Initially the modules have been exposed to outdoor conditions for degradation. Subsequently followed different indoor annealing cycles at various temperatures and heating periods. Annealing effect showed an important recovery already at 80°C, confirming the results of high performances observed for thermal isolated a-Si plants. The most relevant parameter for annealing is temperature, which characterizes the degree of performance recovery and its evolution with time. Annealing effect on power recovery resulted much faster than degradation process. As a matter of fact, annealing at 90-100°C for a period of 8-12 hours allowed an almost complete power recovery in a-Si triple junction modules after 20 days of outdoor degradation in summer time (remaining however below power level at the exit of production line).
Ivano Pola, Domenico Chianese, Lorenzo Fanni. Département fédéral de l'environnement, des transports, de l'énergie et de la communication DETEC. Office fédéral de l'énergie OFEN. Annual Report 2008.
The next step consists in studying annealing and degradation effects directly on modules installed and monitored outdoors. Then these studies will be performed on other a-Si modules most likely of single junction.
Also, this study aims to acquire important knowledge for optimization of amorphous silicon plants and particularly in the case of BiPV solutions.
A comparison of degradation in three amorphous silicon PV module technologies 2010[edit | edit source]
This paper analysis the module degradation of 3 modules. It demonstrated the 80% of initial eff over 20 yr.
C. Radue n, E.E.van Dyk.A comparison of degradation in three amorphous silicon PV module technologies. Solar Energy Materials & Solar Cells 94 (2010) 617–622
INVESTIGATION OF ANNEALING AND DEGRADATION EFFECTS ON A-SI PV MODULES IN REAL OPERATING CONDITIONS 2010[edit | edit source]
This paper looked at the optimal annealing temperature for a triple junction a-Si module. The temperatures ranged from 40-120C and it was found the the best temperature was 90 C for 10-12 hours since it was close to the 120 C but at a lower temp.
Lorenzo Fanni, Ivano Pola, Enrico Burà, Thomas Friesen, Domenico Chianese Institute for applied sustainability to the built environment (ISAAC) University of Applied Sciences of Southern Switzerland (SUPSI) CP 105, CH - 6952 Canobbio Phone: +41 58 / 666 62 90, Fax: +41 58 / 666 63 49 Internet: http://www.isaac.supsi.ch, E-mail: email@example.com
Effects on Amorphous Silicon Photovoltaic Performance from High-temperature Annealing Pulses in Photovoltaic Thermal Hybrid Device[edit | edit source]
Source: M.J.M. Pathak, J.M. Pearce and, S.J. Harrison, "Effects on Amorphous Silicon Photovoltaic Performance from High-temperature Annealing Pulses in Photovoltaic Thermal Hybrid Devices" Solar Energy Materials and Solar Cells, 100, pp. 199-203 (2012). arXiv.
There is a renewed interest in photovoltaic solar thermal (PVT) hybrid systems, which harvest solar energy for heat and electricity. Typically, a main focus of a PVT system is to cool the photovoltaic (PV) cells to improve the electrical performance, however, this causes the thermal component to under-perform compared to a solar thermal collector. The low temperature coefficients of amorphous silicon (a-Si:H) allow for the PV cells to be operated at higher temperatures and are a potential candidate for a more symbiotic PVT system. The fundamental challenge of a-Si:H PV is light-induced degradation known as the Staebler-Wronski effect (SWE). Fortunately, SWE is reversible and the a-Si:H PV efficiency can be returned to its initial state if the cell is annealed. Thus an opportunity exists to deposit a-Si:H directly on the solar thermal absorber plate where the cells could reach the high temperatures required for annealing.
In this study, this opportunity is explored experimentally. First a-Si:H PV cells were annealed for 1 hour at 100C on a 12 hour cycle and for the remaining time the cells were degraded at 50C in order to simulate stagnation of a PVT system for 1 hour once a day. It was found that, when comparing the cells after stabilization at normal 50C degradation, this annealing sequence resulted in a 10.6% energy gain when compared to a cell that was only degraded at 50C.
Optimization of annealing cycles for electric output in outdoor conditions for amorphous silicon photovoltaic–thermal systems[edit | edit source]
- Joseph Rozario and Joshua M. Pearce, Optimization of annealing cycles for electric output in outdoor conditions for amorphous silicon photovoltaic–thermal systems. Applied Energy, 148, pp. 134–141 (2015). DOI: http://dx.doi.org/10.1016/j.apenergy.2015.03.073 open access preprint
- Previous studies with fixed operating temperatures have shown that hydrogenated amorphous silicon (a-Si:H) was a promising absorber layer for solar photovoltaic–thermal (PVT) systems because of (a) a low temperature coefficient and (b) the opportunity to reverse light induced degradation with thermal annealing. This study further refined the simulation of the optimal dispatch strategy for a-Si:H based PVT by studying annealing cycles and analysis of the degradation at other operating temperatures controlled by the varying ambient temperatures. Four representative case studies were evaluated for the combinations of high and low solar flux and high and low average ambient temperature. Electrically-optimized dispatch strategies are found for a range of PVT thermal insulating effectivenesses. The results showed significantly more electricity generation in all the case study representative regions except for areas dominated by low temperatures and low solar fluxes. These results indicate that a-Si:H PV performance can be improved in most populated regions in the world by integrating it into a PVT device and using spike annealing to reverse light-induced degradation effects. The model presented in this paper uses publicly-available data to implement suitable dispatch strategies and execute virtual performance analysis of PVT for any geographic location in the world.