The record efficiency for a thin-film, single-junction solar cell has remained static at 28.8% since 2012. This research presents a unique design that demonstrates potential to exceed record efficiency and approach th...The record efficiency for a thin-film, single-junction solar cell has remained static at 28.8% since 2012. This research presents a unique design that demonstrates potential to exceed record efficiency and approach the theoretical efficiency limit of ~33.5%. The findings of this study are significant, from an efficiency standpoint, and also because the cell design can be realized using existing fabrication methods that do not require complex, post-processing steps. In this study, a benchmark simulation is developed that closely resembles a high-efficiency, front-and-back contact cell. Intrinsic performance limiters are overcome by moving the emitter and front-contact to the back of the cell to eliminate electrical grid shading and improve optical performance. To further improve performance, the P-N junction formed by the emitter layer is removed from the model to allow selective Ohmic contacts to accept (reject) minority (majority) carriers as required. The design modifications improve open-circuit voltage, short-circuit current, and fill-factor which collectively boost efficiency above 30%-primarily due to a 2% gain of incident irradiance and improved optical performance.展开更多
This research builds upon the authors’ previous work that introduced and modeled a novel Gallium-Arsenide, Emitterless, Back-surface Alternating Contact (GaAs-EBAC) thin-film solar cell to achieve >30% power conve...This research builds upon the authors’ previous work that introduced and modeled a novel Gallium-Arsenide, Emitterless, Back-surface Alternating Contact (GaAs-EBAC) thin-film solar cell to achieve >30% power conversion efficiency. Key design parameters are optimized under an Air-Mass (AM) 1.5 spectrum to improve performance and approach the 33.5% theoretical efficiency limit. A second optimization is performed under an AM0 spectrum to examine the cell’s potential for space applications. This research demonstrates the feasibility and potential of a new thin-film solar cell design for terrestrial and space applications. Results suggest that the straight-forward design may be an inexpensive alternative to multi-junction solar cells.展开更多
Direct wafer bonding technology is able to integrate two smooth wafers and thus can be used in fab- ricating III-V multijunction solar cells with lattice mismatch. In order to monolithically interconnect between the G...Direct wafer bonding technology is able to integrate two smooth wafers and thus can be used in fab- ricating III-V multijunction solar cells with lattice mismatch. In order to monolithically interconnect between the GalnP/GaAs and InGaAsP/InGaAs subcells, the bonded GaAs/InP heterojunction must be a highly conductive ohmic junction or a tunnel junction. Three types of bonding interfaces were designed by tuning the conduction type and doping elements of GaAs and InP. The electrical properties of p-GaAs （Zn doped）/n-InP （Si doped）, p- GaAs （C doped）/n-InP （Si doped） and n-GaAs （Si doped）/n-InP （Si doped） bonded heterojunctions were analyzed from the I-V characteristics. The wafer bonding process was investigated by improving the quality of the sample surface and optimizing the bonding parameters such as bonding temperature, bonding pressure, bonding time and so on. Finally, GalnP/GaAs/InGaAsP/lnGaAs 4-junction solar cells have been prepared by a direct wafer bonding technique with the high efficiency of 34.14% at the AM0 condition （1 Sun）.展开更多
Low dislocation density Ge wafers grown by a vertical gradient freeze（VGF） method used for the fabrication of multi-junction photovoltaic cells（MJC） have been studied by a whole wafer scale measurement of the latt...Low dislocation density Ge wafers grown by a vertical gradient freeze（VGF） method used for the fabrication of multi-junction photovoltaic cells（MJC） have been studied by a whole wafer scale measurement of the lattice parameter,X-ray rocking curves,etch pit density（EPD）,impurities concentration,minority carrier lifetime and residual stress.Impurity content in the VGF-Ge wafers,including that of B,is quite low although B_2O_3 encapsulation is used in the growth process.An obvious difference exists across the whole wafer regarding the distribution of etch pit density,lattice parameter,full width at half maximum（FWHM） of the X-ray rocking curve and residual stress measured by Raman spectra.These are in contrast to a reference Ge substrate wafer grown by the Cz method.The influence of the VGF-Ge substrate on the performance of the MJC is analyzed and evaluated by a comparison of the statistical results of cell parameters.展开更多
文摘The record efficiency for a thin-film, single-junction solar cell has remained static at 28.8% since 2012. This research presents a unique design that demonstrates potential to exceed record efficiency and approach the theoretical efficiency limit of ~33.5%. The findings of this study are significant, from an efficiency standpoint, and also because the cell design can be realized using existing fabrication methods that do not require complex, post-processing steps. In this study, a benchmark simulation is developed that closely resembles a high-efficiency, front-and-back contact cell. Intrinsic performance limiters are overcome by moving the emitter and front-contact to the back of the cell to eliminate electrical grid shading and improve optical performance. To further improve performance, the P-N junction formed by the emitter layer is removed from the model to allow selective Ohmic contacts to accept (reject) minority (majority) carriers as required. The design modifications improve open-circuit voltage, short-circuit current, and fill-factor which collectively boost efficiency above 30%-primarily due to a 2% gain of incident irradiance and improved optical performance.
文摘This research builds upon the authors’ previous work that introduced and modeled a novel Gallium-Arsenide, Emitterless, Back-surface Alternating Contact (GaAs-EBAC) thin-film solar cell to achieve >30% power conversion efficiency. Key design parameters are optimized under an Air-Mass (AM) 1.5 spectrum to improve performance and approach the 33.5% theoretical efficiency limit. A second optimization is performed under an AM0 spectrum to examine the cell’s potential for space applications. This research demonstrates the feasibility and potential of a new thin-film solar cell design for terrestrial and space applications. Results suggest that the straight-forward design may be an inexpensive alternative to multi-junction solar cells.
基金Project supported by the Shanghai Rising-Star Program(No.14QB1402800)
文摘Direct wafer bonding technology is able to integrate two smooth wafers and thus can be used in fab- ricating III-V multijunction solar cells with lattice mismatch. In order to monolithically interconnect between the GalnP/GaAs and InGaAsP/InGaAs subcells, the bonded GaAs/InP heterojunction must be a highly conductive ohmic junction or a tunnel junction. Three types of bonding interfaces were designed by tuning the conduction type and doping elements of GaAs and InP. The electrical properties of p-GaAs （Zn doped）/n-InP （Si doped）, p- GaAs （C doped）/n-InP （Si doped） and n-GaAs （Si doped）/n-InP （Si doped） bonded heterojunctions were analyzed from the I-V characteristics. The wafer bonding process was investigated by improving the quality of the sample surface and optimizing the bonding parameters such as bonding temperature, bonding pressure, bonding time and so on. Finally, GalnP/GaAs/InGaAsP/lnGaAs 4-junction solar cells have been prepared by a direct wafer bonding technique with the high efficiency of 34.14% at the AM0 condition （1 Sun）.
基金supported by the National Natural Science Foundation of China(No.61474104)
文摘Low dislocation density Ge wafers grown by a vertical gradient freeze（VGF） method used for the fabrication of multi-junction photovoltaic cells（MJC） have been studied by a whole wafer scale measurement of the lattice parameter,X-ray rocking curves,etch pit density（EPD）,impurities concentration,minority carrier lifetime and residual stress.Impurity content in the VGF-Ge wafers,including that of B,is quite low although B_2O_3 encapsulation is used in the growth process.An obvious difference exists across the whole wafer regarding the distribution of etch pit density,lattice parameter,full width at half maximum（FWHM） of the X-ray rocking curve and residual stress measured by Raman spectra.These are in contrast to a reference Ge substrate wafer grown by the Cz method.The influence of the VGF-Ge substrate on the performance of the MJC is analyzed and evaluated by a comparison of the statistical results of cell parameters.
