Ieee Transactions on Electron Devices, May 1, 1984
The effect of light bias on the spectral current response and spectral capacitance characteristic... more The effect of light bias on the spectral current response and spectral capacitance characteristics of CdS/CuInSe2 thin-film heterojunction solar cells has been investigated. Monochromatic light bias has been used to identify specific wavelength regions responsible for the spectral behavior seen under white light bias. Variations with light or voltage bias are consistent with the effect of the field on interface recombination in both high and low CdS resistivity devices. Devices with high CdS resistivity show spectrally dependent enhancement and quenching effects very similar to those reported for CdS/Cu2S devices in which the space charge region was primarily in the CdS. It is concluded that in high CdS resistivity devices the junction behavior is controlled by the photoconductive CdS as has been established in CdS/Cu2S cells. Low CdS resistivity CdS/CuInSe2 devices show none of these effects.
Current-voltage (JV) analysis of poly (3-hexlythiophene)(P3HT) and phenyl-C61-butaric acid methyl... more Current-voltage (JV) analysis of poly (3-hexlythiophene)(P3HT) and phenyl-C61-butaric acid methyl ester (PCBM) organic photovoltaics (OPV) yield valuable insight into the internal physics of devices. A simple lumped circuit model, previously used to analyze various thin ...
The calculation of the space-charge density under illumination from surface photovoltage measurem... more The calculation of the space-charge density under illumination from surface photovoltage measurements has been adapted to analyze light-soaking experiments in intrinsic hydrogenated amorphous silicon (a-Si:H). We find that the positive space-charge densities increase and the space-charge widths decrease with light exposure while very little change occurs in the hole diffusion length. These results indicate that changes in electric field distribution with light soaking are important causes of degradation of amorphous silicon solar cells, rather than changes which may ocur in the hole diffusion length. We also review and discuss results of others regarding application of the surface photovoltage (SPV) to study light-induced phenomena, evidence of two different types of light-induced defects, and potential limitations of SPV in a-Si:H.
online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastep... more online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste i Summary The overall mission of the Institute of Energy Conversion is the development of thin film photovoltaic cells, modules, and related manufacturing technology and the education of students and professionals in photovoltaic technology. The objectives of this 20 month NREL subcontract are to advance the state of the art and the acceptance of thin film PV modules in the areas of improved technology for thin film deposition, device fabrication, and material and device characterization and modeling, relating to solar cells based on CuInSe 2 and its alloys, on a-Si and its alloys, and on CdTe.
The calculation of the space-charge density under illumination from surface photovoltage measurem... more The calculation of the space-charge density under illumination from surface photovoltage measurements has been adapted to analyze light-soaking experiments in intrinsic hydrogenated amorphous silicon (a-Si:H). We find that the positive space-charge densities increase and the space-charge widths decrease with light exposure while very little change occurs in the hole diffusion length. These results indicate that changes in electric field distribution with light soaking are important causes of degradation of amorphous silicon solar cells, rather than changes which may ocur in the hole diffusion length. We also review and discuss results of others regarding application of the surface photovoltage (SPV) to study light-induced phenomena, evidence of two different types of light-induced defects, and potential limitations of SPV in a-Si:H.
Current transport in a-Si based n/p (‘‘tunnel’’) junctions is investigated using current-voltage-... more Current transport in a-Si based n/p (‘‘tunnel’’) junctions is investigated using current-voltage- temperature and quantum efficiency measurements. Currents are nearly ohmic and temperature independent under typical solar cell operating conditions. Incorporating a thin a-Si(B) p+ layer between the n and p layers and replacing either a-Si layer with a microcrystalline layer improves the device by reducing the resistance and increasing the recombination. Light soaking improves the devices slightly. These results are consistent with a recently proposed recombination-tunneling model. Incorporating improved interconnect junctions in tandem solar cell devices improved the initial and stabilized performance.
online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastep... more online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste i SUMMARY The overall mission of the Institute of Energy Conversion is the development of thin film photovoltaic cells, modules, and related manufacturing technology and the education of students and professionals in photovoltaic technology. The objectives of this 12 month NREL subcontract are to advance the state of the art and the acceptance of thin film PV solar cells in the areas of improved technology for thin film deposition, device fabrication, and material and device characterization and modeling, relating to solar cells based on CuInSe 2 and its alloys, on a-Si and its alloys, and on CdTe.
ABSTRACT We investigate the effect of sputtered transparent conducting oxide (TCO) contacts on th... more ABSTRACT We investigate the effect of sputtered transparent conducting oxide (TCO) contacts on the device performance of ss/n-i-p/TCO and glass/SnO2/p-i-n/TCO/Ag solar cells. TCO materials ITO and ZnO are compared, and found to have very similar transparency at the same sheet resistance. Sputtering ZnO with O2 in the Ar reduces FF for ss/n-i-p/ZnO devices, compared to sputtering without O2. This is attributed to an interface not bulk effect. Sputtering ITO with O2 on the same devices increases JSC due to higher ITO transparency, compared to sputtering without O2 , but has no effect on FF. Based on curvature in the J(V) curve around VOC, the ZnO/p layer contact appears to be non-ohmic. For p-i-n/TCO/Ag devices, μc-Sin-layers have much higher VOC,JSC, and FF for all variations of TCO/Ag back reflectors compared to an a-Si n-layer. Devices with ITO/Ag have lower VOC and JSC compared to devices with ZnO/Ag. Sputtering ZnO with O2 has no detrimental effect on devices with μc-Sin-layers but severely reduces FF in devices with a-Si n-layers.
We present initial results of a study whose goal is to develop a process leading to SiC p-layers ... more We present initial results of a study whose goal is to develop a process leading to SiC p-layers compatible with a superstrate p-i-n cell structure, deposited in an RF PECVD system. Experimental variables were dopant gas, CH 4 and H 2 gas flows normalized to the sum of SiH 4 and CH 4 flows, and the power. Compared to B 2 H 6 , doping with B(CH 3 ) 3 lowered the conductivity by a factor of 40 and reduced the fraction of crystallinity from 87% to 53%. The c-Si fraction decreased strongly with increasing CH 4 flow. No evidence of Si-C bonding was identified in the Raman spectra of these samples. Finally, it has been demonstrated that high conductivity p-layers (>1 S/cm) having high c-Si volume fraction (~85%) can be deposited on glass at low power density (84 mW/cm 2 ) which is compatible with deposition on TCO substrates for device fabrication.
An alternative deposition technique for a-Si:H based thin films is photochemical vapor deposition... more An alternative deposition technique for a-Si:H based thin films is photochemical vapor deposition (photo-CVD) which utilizes UV light to initiate the decomposition of silane or disilane. The best results, from both material properties and device performance points of view, have been achieved using mercury-sensitized photo-CVD. A major problem with photo-CVD can be deposition onto the UV transparent window of the photo-CVD reactor. In this paper we describe a novel photo-CVD reactor that features a movable UVtransparent Teflon ® film and secondary gas flows which effectively eliminate deposition onto the window. The deposition and opto-electronic characterization of intrinsic a-Si:H and a-Sil xGex and of doped films are reported. Preliminary results for p-i n solar cells are presented.
An alternative deposition technique for a-Si:H based thin films is photochemical vapor deposition... more An alternative deposition technique for a-Si:H based thin films is photochemical vapor deposition (photo-CVD) which utilizes UV light to initiate the decomposition of silane or disilane. The best results, from both material properties and device performance points of view, have been achieved using mercury-sensitized photo-CVD. A major problem with photo-CVD can be deposition onto the UV transparent window of the photo-CVD reactor. In this paper we describe a novel photo-CVD reactor that features a movable UVtransparent Teflon ® film and secondary gas flows which effectively eliminate deposition onto the window. The deposition and opto-electronic characterization of intrinsic a-Si:H and a-Sil xGex and of doped films are reported. Preliminary results for p-i n solar cells are presented.
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
Copper sulfide (Cu/sub x/S) films were studied as a back contact material for CdTe solar cells. T... more Copper sulfide (Cu/sub x/S) films were studied as a back contact material for CdTe solar cells. The Cu/sub x/S films were made by chemical bath deposition in aqueous solution. Annealing at 200/spl deg/C in Ar improved the performance of the solar cells. Using the CdS/CdTe/Cu/sub x/S/C structure, an open-circuit voltage (V/sub oc/) higher than 840 mV and an energy conversion efficiency higher than 11% were obtained.
A Thin Film Photovoltaic Symposium was held at the University of Delaware on 1±2 May 1997 to comm... more A Thin Film Photovoltaic Symposium was held at the University of Delaware on 1±2 May 1997 to commemorate the 25th Anniversary of the Institute of Energy Conversion (IEC). The symposium consisted of a morning session on 1 May with invited talks from distinguished representatives from industry, followed by an afternoon session consisting of ®ve interactive workshops. The workshops were run in parallel and each was held twice, allowing participants to attend two workshops. A ceremony was held on 2 May to commemorate the contributions of IEC to the development of thin-®lm photovoltaics over the past 25 years. About 140 people attended the symposium. Financial support was provided in part by the US Department of Energy, National Renewable Energy Laboratory (NREL) and the State of Delaware Economic Development Oce.
The current-voltage characteristics of a Si:H p-i-n solar cells having open-circuit voltages, V(o... more The current-voltage characteristics of a Si:H p-i-n solar cells having open-circuit voltages, V(oc), between 0.70 and 0.90 V were measured as a function of temperature and light intensity. The diode parameters (diode factor, saturation current density, and built-in voltage) were calculated in the light and in the dark. It was found that parameters obtained in the dark have no relevance to the analysis of V(oc), but they do indicate that tunneling may have a significant effect in the dark. The V(oc) is dominated by recombination at the p/i interface or in the i layer near this interface. Reducing interface recombination with a carbon buffer layer and reducing bulk recombination with less i layer impurities improves V(oc) by reducing the forward recombination current density.
Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996, 1996
The primary purpose of the present paper is to evaluate the effect of a number of textured SnO 2 ... more The primary purpose of the present paper is to evaluate the effect of a number of textured SnO 2 and ZnO substrates on the current generation in a-Si solar cells. This work is of relevance since most of these TCOs have been used by others for a-Si device research or module fabrication. Secondarily, some qualitative observations will also be made on the relative quality of the electrical contact between the TCOs investigated and the a-Si p-layers. Bulk optoelectronic and structural properties are reported for seven TCO films with haze from 1 to 14%. Our results show that increasing haze above ~7% for SnO 2 and ~5% for ZnO has limited effectiveness for increasing the generation at long wavelengths. With presently available textured ZnO, current generation is about 0.6 mA/cm 2 greater than with textured SnO 2 . There may be other advantages to using ZnO in multijunction devices since thinner i-layers may be used to give the same J sc with improved stability.
Ieee Transactions on Electron Devices, May 1, 1984
The effect of light bias on the spectral current response and spectral capacitance characteristic... more The effect of light bias on the spectral current response and spectral capacitance characteristics of CdS/CuInSe2 thin-film heterojunction solar cells has been investigated. Monochromatic light bias has been used to identify specific wavelength regions responsible for the spectral behavior seen under white light bias. Variations with light or voltage bias are consistent with the effect of the field on interface recombination in both high and low CdS resistivity devices. Devices with high CdS resistivity show spectrally dependent enhancement and quenching effects very similar to those reported for CdS/Cu2S devices in which the space charge region was primarily in the CdS. It is concluded that in high CdS resistivity devices the junction behavior is controlled by the photoconductive CdS as has been established in CdS/Cu2S cells. Low CdS resistivity CdS/CuInSe2 devices show none of these effects.
Current-voltage (JV) analysis of poly (3-hexlythiophene)(P3HT) and phenyl-C61-butaric acid methyl... more Current-voltage (JV) analysis of poly (3-hexlythiophene)(P3HT) and phenyl-C61-butaric acid methyl ester (PCBM) organic photovoltaics (OPV) yield valuable insight into the internal physics of devices. A simple lumped circuit model, previously used to analyze various thin ...
The calculation of the space-charge density under illumination from surface photovoltage measurem... more The calculation of the space-charge density under illumination from surface photovoltage measurements has been adapted to analyze light-soaking experiments in intrinsic hydrogenated amorphous silicon (a-Si:H). We find that the positive space-charge densities increase and the space-charge widths decrease with light exposure while very little change occurs in the hole diffusion length. These results indicate that changes in electric field distribution with light soaking are important causes of degradation of amorphous silicon solar cells, rather than changes which may ocur in the hole diffusion length. We also review and discuss results of others regarding application of the surface photovoltage (SPV) to study light-induced phenomena, evidence of two different types of light-induced defects, and potential limitations of SPV in a-Si:H.
online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastep... more online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste i Summary The overall mission of the Institute of Energy Conversion is the development of thin film photovoltaic cells, modules, and related manufacturing technology and the education of students and professionals in photovoltaic technology. The objectives of this 20 month NREL subcontract are to advance the state of the art and the acceptance of thin film PV modules in the areas of improved technology for thin film deposition, device fabrication, and material and device characterization and modeling, relating to solar cells based on CuInSe 2 and its alloys, on a-Si and its alloys, and on CdTe.
The calculation of the space-charge density under illumination from surface photovoltage measurem... more The calculation of the space-charge density under illumination from surface photovoltage measurements has been adapted to analyze light-soaking experiments in intrinsic hydrogenated amorphous silicon (a-Si:H). We find that the positive space-charge densities increase and the space-charge widths decrease with light exposure while very little change occurs in the hole diffusion length. These results indicate that changes in electric field distribution with light soaking are important causes of degradation of amorphous silicon solar cells, rather than changes which may ocur in the hole diffusion length. We also review and discuss results of others regarding application of the surface photovoltage (SPV) to study light-induced phenomena, evidence of two different types of light-induced defects, and potential limitations of SPV in a-Si:H.
Current transport in a-Si based n/p (‘‘tunnel’’) junctions is investigated using current-voltage-... more Current transport in a-Si based n/p (‘‘tunnel’’) junctions is investigated using current-voltage- temperature and quantum efficiency measurements. Currents are nearly ohmic and temperature independent under typical solar cell operating conditions. Incorporating a thin a-Si(B) p+ layer between the n and p layers and replacing either a-Si layer with a microcrystalline layer improves the device by reducing the resistance and increasing the recombination. Light soaking improves the devices slightly. These results are consistent with a recently proposed recombination-tunneling model. Incorporating improved interconnect junctions in tandem solar cell devices improved the initial and stabilized performance.
online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastep... more online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste i SUMMARY The overall mission of the Institute of Energy Conversion is the development of thin film photovoltaic cells, modules, and related manufacturing technology and the education of students and professionals in photovoltaic technology. The objectives of this 12 month NREL subcontract are to advance the state of the art and the acceptance of thin film PV solar cells in the areas of improved technology for thin film deposition, device fabrication, and material and device characterization and modeling, relating to solar cells based on CuInSe 2 and its alloys, on a-Si and its alloys, and on CdTe.
ABSTRACT We investigate the effect of sputtered transparent conducting oxide (TCO) contacts on th... more ABSTRACT We investigate the effect of sputtered transparent conducting oxide (TCO) contacts on the device performance of ss/n-i-p/TCO and glass/SnO2/p-i-n/TCO/Ag solar cells. TCO materials ITO and ZnO are compared, and found to have very similar transparency at the same sheet resistance. Sputtering ZnO with O2 in the Ar reduces FF for ss/n-i-p/ZnO devices, compared to sputtering without O2. This is attributed to an interface not bulk effect. Sputtering ITO with O2 on the same devices increases JSC due to higher ITO transparency, compared to sputtering without O2 , but has no effect on FF. Based on curvature in the J(V) curve around VOC, the ZnO/p layer contact appears to be non-ohmic. For p-i-n/TCO/Ag devices, μc-Sin-layers have much higher VOC,JSC, and FF for all variations of TCO/Ag back reflectors compared to an a-Si n-layer. Devices with ITO/Ag have lower VOC and JSC compared to devices with ZnO/Ag. Sputtering ZnO with O2 has no detrimental effect on devices with μc-Sin-layers but severely reduces FF in devices with a-Si n-layers.
We present initial results of a study whose goal is to develop a process leading to SiC p-layers ... more We present initial results of a study whose goal is to develop a process leading to SiC p-layers compatible with a superstrate p-i-n cell structure, deposited in an RF PECVD system. Experimental variables were dopant gas, CH 4 and H 2 gas flows normalized to the sum of SiH 4 and CH 4 flows, and the power. Compared to B 2 H 6 , doping with B(CH 3 ) 3 lowered the conductivity by a factor of 40 and reduced the fraction of crystallinity from 87% to 53%. The c-Si fraction decreased strongly with increasing CH 4 flow. No evidence of Si-C bonding was identified in the Raman spectra of these samples. Finally, it has been demonstrated that high conductivity p-layers (>1 S/cm) having high c-Si volume fraction (~85%) can be deposited on glass at low power density (84 mW/cm 2 ) which is compatible with deposition on TCO substrates for device fabrication.
An alternative deposition technique for a-Si:H based thin films is photochemical vapor deposition... more An alternative deposition technique for a-Si:H based thin films is photochemical vapor deposition (photo-CVD) which utilizes UV light to initiate the decomposition of silane or disilane. The best results, from both material properties and device performance points of view, have been achieved using mercury-sensitized photo-CVD. A major problem with photo-CVD can be deposition onto the UV transparent window of the photo-CVD reactor. In this paper we describe a novel photo-CVD reactor that features a movable UVtransparent Teflon ® film and secondary gas flows which effectively eliminate deposition onto the window. The deposition and opto-electronic characterization of intrinsic a-Si:H and a-Sil xGex and of doped films are reported. Preliminary results for p-i n solar cells are presented.
An alternative deposition technique for a-Si:H based thin films is photochemical vapor deposition... more An alternative deposition technique for a-Si:H based thin films is photochemical vapor deposition (photo-CVD) which utilizes UV light to initiate the decomposition of silane or disilane. The best results, from both material properties and device performance points of view, have been achieved using mercury-sensitized photo-CVD. A major problem with photo-CVD can be deposition onto the UV transparent window of the photo-CVD reactor. In this paper we describe a novel photo-CVD reactor that features a movable UVtransparent Teflon ® film and secondary gas flows which effectively eliminate deposition onto the window. The deposition and opto-electronic characterization of intrinsic a-Si:H and a-Sil xGex and of doped films are reported. Preliminary results for p-i n solar cells are presented.
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
Copper sulfide (Cu/sub x/S) films were studied as a back contact material for CdTe solar cells. T... more Copper sulfide (Cu/sub x/S) films were studied as a back contact material for CdTe solar cells. The Cu/sub x/S films were made by chemical bath deposition in aqueous solution. Annealing at 200/spl deg/C in Ar improved the performance of the solar cells. Using the CdS/CdTe/Cu/sub x/S/C structure, an open-circuit voltage (V/sub oc/) higher than 840 mV and an energy conversion efficiency higher than 11% were obtained.
A Thin Film Photovoltaic Symposium was held at the University of Delaware on 1±2 May 1997 to comm... more A Thin Film Photovoltaic Symposium was held at the University of Delaware on 1±2 May 1997 to commemorate the 25th Anniversary of the Institute of Energy Conversion (IEC). The symposium consisted of a morning session on 1 May with invited talks from distinguished representatives from industry, followed by an afternoon session consisting of ®ve interactive workshops. The workshops were run in parallel and each was held twice, allowing participants to attend two workshops. A ceremony was held on 2 May to commemorate the contributions of IEC to the development of thin-®lm photovoltaics over the past 25 years. About 140 people attended the symposium. Financial support was provided in part by the US Department of Energy, National Renewable Energy Laboratory (NREL) and the State of Delaware Economic Development Oce.
The current-voltage characteristics of a Si:H p-i-n solar cells having open-circuit voltages, V(o... more The current-voltage characteristics of a Si:H p-i-n solar cells having open-circuit voltages, V(oc), between 0.70 and 0.90 V were measured as a function of temperature and light intensity. The diode parameters (diode factor, saturation current density, and built-in voltage) were calculated in the light and in the dark. It was found that parameters obtained in the dark have no relevance to the analysis of V(oc), but they do indicate that tunneling may have a significant effect in the dark. The V(oc) is dominated by recombination at the p/i interface or in the i layer near this interface. Reducing interface recombination with a carbon buffer layer and reducing bulk recombination with less i layer impurities improves V(oc) by reducing the forward recombination current density.
Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996, 1996
The primary purpose of the present paper is to evaluate the effect of a number of textured SnO 2 ... more The primary purpose of the present paper is to evaluate the effect of a number of textured SnO 2 and ZnO substrates on the current generation in a-Si solar cells. This work is of relevance since most of these TCOs have been used by others for a-Si device research or module fabrication. Secondarily, some qualitative observations will also be made on the relative quality of the electrical contact between the TCOs investigated and the a-Si p-layers. Bulk optoelectronic and structural properties are reported for seven TCO films with haze from 1 to 14%. Our results show that increasing haze above ~7% for SnO 2 and ~5% for ZnO has limited effectiveness for increasing the generation at long wavelengths. With presently available textured ZnO, current generation is about 0.6 mA/cm 2 greater than with textured SnO 2 . There may be other advantages to using ZnO in multijunction devices since thinner i-layers may be used to give the same J sc with improved stability.
Uploads
Papers by Steven Hegedus