Predicting the energy generation of a photovoltaic (PV) system and calculating the levelized cost... more Predicting the energy generation of a photovoltaic (PV) system and calculating the levelized cost of electricity (LCOE) is highly dependent on the solar resources, the climate and the temperature coefficients of the PV modules. In this work, the uncertainties in measuring PV module's temperature coefficients are investigated. The paper includes a brief theoretical study of the temperature coefficient calculation, the analytical and experimental results. Measurement results in our laboratory show that (i) the non-uniformity of temperature across a module, (ii) the error in measuring the solar cell's real temperature during an IV measurement and (iii) variations in a flash light simulator's spectrum are the three main factors of the uncertainties. Furthermore, three modules have been selected for a round-robin test in several PV testing laboratories around the world. The results show that the variation in measured temperature coefficients of Pmax arising from different measurement procedures is up to +/-0.04%/˚C, or +/- 10% in relative value. It is found that the bulk of the uncertainty is in the inaccuracy of measuring the real cell temperature. For silicon solar cells fabricated with similar technologies and having similar efficiencies, their temperature coefficient of Pmax is expected to be almost identical. This study shows that the main difference between the temperature coefficients on data sheets comes from the different measurement methods used.
A maximum open-circuit voltage of 702 mV and a full area efficiency of 24.13% has been achieved o... more A maximum open-circuit voltage of 702 mV and a full area efficiency of 24.13% has been achieved on 6 inch square n-type CZ wafer with a Interdigitated Back Contact (IBC) cell structure, without utilizing the technology of passivated contacts. Conventional industrially feasible and low cost processes are used for this cell fabrication. This result is achieved by applying a selective emitter structure, improved surface passivation and redesigned rear pattern with the assistance of numerical simulation. The contact resistivity on both emitter and BSF region is reduced to less than 0.5 mcm2. The power loss analysis shows that the biggest recombination loss is within the bulk, summing up to 45% of the total recombination current at Pmpp.
Conference Record of the Twenty-Eighth IEEE Photovoltaic Specialists Conference - 2000 (Cat. No.00CH37036)
ABSTRACT We find that the front surface quality on back contacted silicon solar cells is degraded... more ABSTRACT We find that the front surface quality on back contacted silicon solar cells is degraded by the evaporative deposition of an anti-reflective coating. The degradation is most severe when an e-beam evaporation is performed, but there is still significant degradation with thermal evaporation. The surface recovers some after a forming gas anneal but is still degraded compared to before the evaporation. The degradation overwhelms and negates any forming gas anneal performed prior to the evaporation. The degradation is greatly reduced if the surface is not textured. We discuss the application of these results to our high efficiency silicon solar cells
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
SLIVER modules differ significantly from conventional crystalline silicon modules due to the uniq... more SLIVER modules differ significantly from conventional crystalline silicon modules due to the unique geometry and performance of SLIVER solar cells. This offers many performance advantages including excellent resistance to shading, low temperature coefficient and flexible output characteristics while demonstrating good robustness during reliability testing
In this work, a route towards high efficiency n-type solar cells with a Passivated Emitter and Re... more In this work, a route towards high efficiency n-type solar cells with a Passivated Emitter and Rear Totally Diffused (PERT) structure done by a combination of characterization and modeling is presented. Low cost industrial processes such as tube diffusion and plating have been used for the fabrication. Optimization result on emitter profile shows that shallower junction depth emitter with 93 ohm/sq sheet resistance brings a 0.23% absolute efficiency gain. A champion efficiency of 22.40% has been achieved on 6 inch CZ wafers after further optimization of front finger and rear pitch. The semicondutor device simulation software Sentaurus is used to reveal that injection-dependent lifetime due to shallow defects enhance the fill factor in n-type solar cells.
ABSTRACT The quality of screen printed Al Back Surface Field (Al-BSF) on alkaline textured, polis... more ABSTRACT The quality of screen printed Al Back Surface Field (Al-BSF) on alkaline textured, polished or acid-textured surface was investigated. Al paste was screen-printed on a full rear surface of silicon wafers and Al-BSF was formed during firing process in a belt furnace. The morphology of the formed Al-BSFs was observed by Scanning Electron Microscopy (SEM). Compared to an alkaline textured surface, the Si/BSF interface on a polished surface is smoother, and the Al-BSF is continuous. J0 was measured by photoconductivity decay (PCD) and the J0,BSF of different kinds of rear surfaces were compared. It was observed that J0,BSF is strongly affected by Al-BSF uniformity. J0,BSF of polished surfaces is about 40fA/cm2 less than J0,BSF of alkaline textured surfaces. Through PC1D simulation, the increase in cell efficiency was calculated to be about 0.08% absolute due to the decrease in J0,BSF.
ABSTRACT In this work, ozone dissolved in deionized water (DIO 3) cleaning is investigated as a l... more ABSTRACT In this work, ozone dissolved in deionized water (DIO 3) cleaning is investigated as a low-cost alternative method to the current wet-chemical cleaning in high-efficiency solar cell manufacturing. Higher effective lifetime and lower J 0 were achieved, compared to the reference cleaning process of high-lifetime RCA, by simply adding a small amount of HF and HCl to DIO 3 solution. The effective lifetime of cleaned and passivated wafers increased as the processing time in DIO 3 /HF/HCl cleaning solution increased. The stability of the wafer lifetime even after some storage time of up to an hour post cleaning makes the DIO 3 /HF/HCl cleaning suitable for industrial application. The DIO 3 /HF/HCl cleaning shows a great potential to be a high-lifetime wet-chemical cleaning process in mass production.
ABSTRACT For many years, selective emitter (SE) silicon solar cells have demonstrated higher effi... more ABSTRACT For many years, selective emitter (SE) silicon solar cells have demonstrated higher efficiency than homogeneous emitter (HE) solar cells. SE solar cells are now commonly manufactured in industrial mass production. The efficiency gain is however limited by the practical sheet resistance attainable for heavily and lightly doped emitters. An optimized two-step diffusion process for making SE solar cells with a low doping concentration emitter is investigated and compared to the conventional one-step diffusion. An emitter with sheet resistance of 60Ω/□ was diffused by a two-step diffusion process. An emitter with sheet resistance of 65Ω/□ as a baseline reference was fabricated and compared. After inkjet printing of mask paste and an etch-back process, a sheet resistance of 140Ω/□ was obtained for these two types of diffusion. The etching rate for both emitters was studied. The total saturation current density, J 0,total , for an optimized emitter shows reduction of about 21 fA/cm 2 compared to that of the reference emitter. This reduction in J 0e corresponds to an average V oc increase of about 3.9 mV, as demonstrated experimentally. The conversion efficiency of solar cells with the optimized emitter increases approximately by 0.1% abs compared to the reference cell. Internal quantum efficiency and reflectance were compared for these two types of SE solar cells.
PV modules are optimized for particular climates in terms of reliability and energy efficiency, i... more PV modules are optimized for particular climates in terms of reliability and energy efficiency, instead of being optimized for a standard testing condition of 1000W/m2, 25°C cell temperature. A dual-glass PV module has been designed and developed for harsh climates, such as desert hot-dry, tropical hot-humid and mountain cold-sunny climates. The dual-glass module is optimized to deliver the highest amount of annual energy, i.e. optimized for energy efficiency instead of power efficiency at STC, as well as optimized for best reliability for the particular climatic conditions. Reliability test sequences must be adapted to the particular climatic environment. Dual Glass modules present excellent reliability for the harshest climatic environment such as desert, tropical and mountain climates. Dual Glass modules have shown the best resistance to reliability tests, up to more than three times the standard IEC 61215, as well as an excellent resistance to the System Voltage Durability test or commonly called PID test for 600 hours under 85% R.H., 85°C, 1500V, or even the most stringent test for 600 hours under 85% R.H., 85°C, 1000V with Cu foil, with a degradation of less than 3%.
A detailed investigation of the reliability of PV modules using a low-temperature conductive film... more A detailed investigation of the reliability of PV modules using a low-temperature conductive film interconnection process is presented. An advanced low-temperature conductive film bonding technology is compared to the conventional soldering process. The reliability of PV modules with different interconnection processes is analyzed by up to two times the standard module reliability testing sequences. At the material level, the stability of the contact resistance is analyzed under different temperatures. The results show that, compared to the conventional soldering process, the low-temperature conductive film bonding technology exhibits a comparable reliability, benefiting from low stress thanks to a low-temperature process. This analysis demonstrates the potential for long durability of the cross-linked conductive film. Besides, low temperature interconnection technology may be combined with other advanced technologies to achieve higher module power.
Point-contact silicon solar cells have been developed for Fresnel lens concentrator modules. The ... more Point-contact silicon solar cells have been developed for Fresnel lens concentrator modules. The cells have an area of 1.21 cm2 on a 12×12 mm die. The design incident flux on the cell is 22.3 W/cm2. A new cell design and process have been developed to insure a high efficiency and a large fabrication yield, and to eliminate hazardous materials and pyrophoric gases. The new process is very safe and benign to the environment. Also, a new passivation technique for the front surface has been discovered which makes the point-contact cell fully stable under steady-state concentrated sunlight. No degradation has been observed so far after more than 200 days of exposure behind Fresnel lenses providing an incident power density of 36 W/cm2. An improved anti-reflection coating and an improved light trapping, giving an average effective number of passes of the infra-red light greater than 25, are part of the developments. The best cell shows an efficiency of 26% under 100 suns (AM1.5D, 25°C). T...
Conference Record of the IEEE Photovoltaic Specialists Conference
A 10 kW reflective dish PV system is under development by SunPower Corporation. Two of these syst... more A 10 kW reflective dish PV system is under development by SunPower Corporation. Two of these systems are designed for installation at the PVUSA (Photovoltaics for Utility-Scale Application, a consortium of utilities and public entities) test site in CA, USA. The PV modules are monolithic “dense arrays” of ten cells, fabricated and series/parallel connected on a single silicon wafer and mounted on water-cooled cold plates. The cells are point-contact backside silicon, currently of about 20% efficiency at 20 W/cm2 [AM 1.5 D, 25 °C]. When recent techniques employed in producing smaller cells having 26% efficiency are incorporated, 23.5% module efficiency and 16% system efficiency are projected. The mirrored dish is comprised of 0.3048×3.048 M (1×10 ft) curved strips of second-surface low-iron glass mirrors. The tracker is a conventional two-axis design. Focal length is 8.5 m (28 ft); concentration is 250×. A 1/3-scale 1 kW prototype dish has been built and is undergoing testing at SunP...
Conference Record of the IEEE Photovoltaic Specialists Conference
In this paper, the authors report on the development of high-efficiency silicon solar cells desig... more In this paper, the authors report on the development of high-efficiency silicon solar cells designed specifically for space applications. The cells are the 100 μm thin N+-P-P+ and are 2×4 cm in size. The front side surface is textured with inverted pyramids and received a double layer anti-reflection coating (ARC). They also have a back surface field (BSF) and a back surface reflector (BSR). Both front and back diffusions are optimized for radiation hardness. The best beginning of life (BOL) efficiencies of these thin (100 μm) 2 cm×4 cm cells have been measured At JPL to be 18.3%. The best end of life (EOL) efficiencies after 1 MeV 1E15 electrons is 12.1%
We present a new concept for thin silicon solar cells. In the LASE process (Lateral Anisotropic S... more We present a new concept for thin silicon solar cells. In the LASE process (Lateral Anisotropic Silicon Etching) shallow grooves are cut into a (111) oriented silicon wafer at regular intervals. Using alkaline etching, lateral channels are formed which extend underneath the silicon wafer and eventually meet to detach the silicon layer on top. Unlike other liftoff techniques, no silicon deposition is required. The technique can be used to produce silicon strips as well as continuous sheets. Silicon strips can be used to fabricate monolithically connected solar cells and high voltage, low current modules.
Predicting the energy generation of a photovoltaic (PV) system and calculating the levelized cost... more Predicting the energy generation of a photovoltaic (PV) system and calculating the levelized cost of electricity (LCOE) is highly dependent on the solar resources, the climate and the temperature coefficients of the PV modules. In this work, the uncertainties in measuring PV module's temperature coefficients are investigated. The paper includes a brief theoretical study of the temperature coefficient calculation, the analytical and experimental results. Measurement results in our laboratory show that (i) the non-uniformity of temperature across a module, (ii) the error in measuring the solar cell's real temperature during an IV measurement and (iii) variations in a flash light simulator's spectrum are the three main factors of the uncertainties. Furthermore, three modules have been selected for a round-robin test in several PV testing laboratories around the world. The results show that the variation in measured temperature coefficients of Pmax arising from different measurement procedures is up to +/-0.04%/˚C, or +/- 10% in relative value. It is found that the bulk of the uncertainty is in the inaccuracy of measuring the real cell temperature. For silicon solar cells fabricated with similar technologies and having similar efficiencies, their temperature coefficient of Pmax is expected to be almost identical. This study shows that the main difference between the temperature coefficients on data sheets comes from the different measurement methods used.
A maximum open-circuit voltage of 702 mV and a full area efficiency of 24.13% has been achieved o... more A maximum open-circuit voltage of 702 mV and a full area efficiency of 24.13% has been achieved on 6 inch square n-type CZ wafer with a Interdigitated Back Contact (IBC) cell structure, without utilizing the technology of passivated contacts. Conventional industrially feasible and low cost processes are used for this cell fabrication. This result is achieved by applying a selective emitter structure, improved surface passivation and redesigned rear pattern with the assistance of numerical simulation. The contact resistivity on both emitter and BSF region is reduced to less than 0.5 mcm2. The power loss analysis shows that the biggest recombination loss is within the bulk, summing up to 45% of the total recombination current at Pmpp.
Conference Record of the Twenty-Eighth IEEE Photovoltaic Specialists Conference - 2000 (Cat. No.00CH37036)
ABSTRACT We find that the front surface quality on back contacted silicon solar cells is degraded... more ABSTRACT We find that the front surface quality on back contacted silicon solar cells is degraded by the evaporative deposition of an anti-reflective coating. The degradation is most severe when an e-beam evaporation is performed, but there is still significant degradation with thermal evaporation. The surface recovers some after a forming gas anneal but is still degraded compared to before the evaporation. The degradation overwhelms and negates any forming gas anneal performed prior to the evaporation. The degradation is greatly reduced if the surface is not textured. We discuss the application of these results to our high efficiency silicon solar cells
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
SLIVER modules differ significantly from conventional crystalline silicon modules due to the uniq... more SLIVER modules differ significantly from conventional crystalline silicon modules due to the unique geometry and performance of SLIVER solar cells. This offers many performance advantages including excellent resistance to shading, low temperature coefficient and flexible output characteristics while demonstrating good robustness during reliability testing
In this work, a route towards high efficiency n-type solar cells with a Passivated Emitter and Re... more In this work, a route towards high efficiency n-type solar cells with a Passivated Emitter and Rear Totally Diffused (PERT) structure done by a combination of characterization and modeling is presented. Low cost industrial processes such as tube diffusion and plating have been used for the fabrication. Optimization result on emitter profile shows that shallower junction depth emitter with 93 ohm/sq sheet resistance brings a 0.23% absolute efficiency gain. A champion efficiency of 22.40% has been achieved on 6 inch CZ wafers after further optimization of front finger and rear pitch. The semicondutor device simulation software Sentaurus is used to reveal that injection-dependent lifetime due to shallow defects enhance the fill factor in n-type solar cells.
ABSTRACT The quality of screen printed Al Back Surface Field (Al-BSF) on alkaline textured, polis... more ABSTRACT The quality of screen printed Al Back Surface Field (Al-BSF) on alkaline textured, polished or acid-textured surface was investigated. Al paste was screen-printed on a full rear surface of silicon wafers and Al-BSF was formed during firing process in a belt furnace. The morphology of the formed Al-BSFs was observed by Scanning Electron Microscopy (SEM). Compared to an alkaline textured surface, the Si/BSF interface on a polished surface is smoother, and the Al-BSF is continuous. J0 was measured by photoconductivity decay (PCD) and the J0,BSF of different kinds of rear surfaces were compared. It was observed that J0,BSF is strongly affected by Al-BSF uniformity. J0,BSF of polished surfaces is about 40fA/cm2 less than J0,BSF of alkaline textured surfaces. Through PC1D simulation, the increase in cell efficiency was calculated to be about 0.08% absolute due to the decrease in J0,BSF.
ABSTRACT In this work, ozone dissolved in deionized water (DIO 3) cleaning is investigated as a l... more ABSTRACT In this work, ozone dissolved in deionized water (DIO 3) cleaning is investigated as a low-cost alternative method to the current wet-chemical cleaning in high-efficiency solar cell manufacturing. Higher effective lifetime and lower J 0 were achieved, compared to the reference cleaning process of high-lifetime RCA, by simply adding a small amount of HF and HCl to DIO 3 solution. The effective lifetime of cleaned and passivated wafers increased as the processing time in DIO 3 /HF/HCl cleaning solution increased. The stability of the wafer lifetime even after some storage time of up to an hour post cleaning makes the DIO 3 /HF/HCl cleaning suitable for industrial application. The DIO 3 /HF/HCl cleaning shows a great potential to be a high-lifetime wet-chemical cleaning process in mass production.
ABSTRACT For many years, selective emitter (SE) silicon solar cells have demonstrated higher effi... more ABSTRACT For many years, selective emitter (SE) silicon solar cells have demonstrated higher efficiency than homogeneous emitter (HE) solar cells. SE solar cells are now commonly manufactured in industrial mass production. The efficiency gain is however limited by the practical sheet resistance attainable for heavily and lightly doped emitters. An optimized two-step diffusion process for making SE solar cells with a low doping concentration emitter is investigated and compared to the conventional one-step diffusion. An emitter with sheet resistance of 60Ω/□ was diffused by a two-step diffusion process. An emitter with sheet resistance of 65Ω/□ as a baseline reference was fabricated and compared. After inkjet printing of mask paste and an etch-back process, a sheet resistance of 140Ω/□ was obtained for these two types of diffusion. The etching rate for both emitters was studied. The total saturation current density, J 0,total , for an optimized emitter shows reduction of about 21 fA/cm 2 compared to that of the reference emitter. This reduction in J 0e corresponds to an average V oc increase of about 3.9 mV, as demonstrated experimentally. The conversion efficiency of solar cells with the optimized emitter increases approximately by 0.1% abs compared to the reference cell. Internal quantum efficiency and reflectance were compared for these two types of SE solar cells.
PV modules are optimized for particular climates in terms of reliability and energy efficiency, i... more PV modules are optimized for particular climates in terms of reliability and energy efficiency, instead of being optimized for a standard testing condition of 1000W/m2, 25°C cell temperature. A dual-glass PV module has been designed and developed for harsh climates, such as desert hot-dry, tropical hot-humid and mountain cold-sunny climates. The dual-glass module is optimized to deliver the highest amount of annual energy, i.e. optimized for energy efficiency instead of power efficiency at STC, as well as optimized for best reliability for the particular climatic conditions. Reliability test sequences must be adapted to the particular climatic environment. Dual Glass modules present excellent reliability for the harshest climatic environment such as desert, tropical and mountain climates. Dual Glass modules have shown the best resistance to reliability tests, up to more than three times the standard IEC 61215, as well as an excellent resistance to the System Voltage Durability test or commonly called PID test for 600 hours under 85% R.H., 85°C, 1500V, or even the most stringent test for 600 hours under 85% R.H., 85°C, 1000V with Cu foil, with a degradation of less than 3%.
A detailed investigation of the reliability of PV modules using a low-temperature conductive film... more A detailed investigation of the reliability of PV modules using a low-temperature conductive film interconnection process is presented. An advanced low-temperature conductive film bonding technology is compared to the conventional soldering process. The reliability of PV modules with different interconnection processes is analyzed by up to two times the standard module reliability testing sequences. At the material level, the stability of the contact resistance is analyzed under different temperatures. The results show that, compared to the conventional soldering process, the low-temperature conductive film bonding technology exhibits a comparable reliability, benefiting from low stress thanks to a low-temperature process. This analysis demonstrates the potential for long durability of the cross-linked conductive film. Besides, low temperature interconnection technology may be combined with other advanced technologies to achieve higher module power.
Point-contact silicon solar cells have been developed for Fresnel lens concentrator modules. The ... more Point-contact silicon solar cells have been developed for Fresnel lens concentrator modules. The cells have an area of 1.21 cm2 on a 12×12 mm die. The design incident flux on the cell is 22.3 W/cm2. A new cell design and process have been developed to insure a high efficiency and a large fabrication yield, and to eliminate hazardous materials and pyrophoric gases. The new process is very safe and benign to the environment. Also, a new passivation technique for the front surface has been discovered which makes the point-contact cell fully stable under steady-state concentrated sunlight. No degradation has been observed so far after more than 200 days of exposure behind Fresnel lenses providing an incident power density of 36 W/cm2. An improved anti-reflection coating and an improved light trapping, giving an average effective number of passes of the infra-red light greater than 25, are part of the developments. The best cell shows an efficiency of 26% under 100 suns (AM1.5D, 25°C). T...
Conference Record of the IEEE Photovoltaic Specialists Conference
A 10 kW reflective dish PV system is under development by SunPower Corporation. Two of these syst... more A 10 kW reflective dish PV system is under development by SunPower Corporation. Two of these systems are designed for installation at the PVUSA (Photovoltaics for Utility-Scale Application, a consortium of utilities and public entities) test site in CA, USA. The PV modules are monolithic “dense arrays” of ten cells, fabricated and series/parallel connected on a single silicon wafer and mounted on water-cooled cold plates. The cells are point-contact backside silicon, currently of about 20% efficiency at 20 W/cm2 [AM 1.5 D, 25 °C]. When recent techniques employed in producing smaller cells having 26% efficiency are incorporated, 23.5% module efficiency and 16% system efficiency are projected. The mirrored dish is comprised of 0.3048×3.048 M (1×10 ft) curved strips of second-surface low-iron glass mirrors. The tracker is a conventional two-axis design. Focal length is 8.5 m (28 ft); concentration is 250×. A 1/3-scale 1 kW prototype dish has been built and is undergoing testing at SunP...
Conference Record of the IEEE Photovoltaic Specialists Conference
In this paper, the authors report on the development of high-efficiency silicon solar cells desig... more In this paper, the authors report on the development of high-efficiency silicon solar cells designed specifically for space applications. The cells are the 100 μm thin N+-P-P+ and are 2×4 cm in size. The front side surface is textured with inverted pyramids and received a double layer anti-reflection coating (ARC). They also have a back surface field (BSF) and a back surface reflector (BSR). Both front and back diffusions are optimized for radiation hardness. The best beginning of life (BOL) efficiencies of these thin (100 μm) 2 cm×4 cm cells have been measured At JPL to be 18.3%. The best end of life (EOL) efficiencies after 1 MeV 1E15 electrons is 12.1%
We present a new concept for thin silicon solar cells. In the LASE process (Lateral Anisotropic S... more We present a new concept for thin silicon solar cells. In the LASE process (Lateral Anisotropic Silicon Etching) shallow grooves are cut into a (111) oriented silicon wafer at regular intervals. Using alkaline etching, lateral channels are formed which extend underneath the silicon wafer and eventually meet to detach the silicon layer on top. Unlike other liftoff techniques, no silicon deposition is required. The technique can be used to produce silicon strips as well as continuous sheets. Silicon strips can be used to fabricate monolithically connected solar cells and high voltage, low current modules.
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Papers by Pierre Verlinden