OPTIMUM DESIGN AND ITS EXPERIMENTAL APPROACH OF A-SI/POLY-SI TANDEM SOLAR-CELL

A series of technical data on four-terminal a-Si//poly-Si stacked solar cells has been reported. The developed device has some unique significances such as high achievable efficiency, and low cost with almost no light induced degradation. It has been shown on a poly-Si bottom cell that an efficiency of 17.2% has been obtained by employing high conductivity with wide optical band-gap p-type muc-SiC as a window material and n-type muc-SiC as a back ohmic contact with BSF effects. On the optically transparent a-Si top cell, an optimum design has been experimentally made with the device structure of p muc-SiC/p a-SiC/i a-Si/n muc-Si/ITO, and an efficiency of 7.25% has been obtained with a 100 nm thick i-layer, while the best efficiency is 12.3% for p-i-n single-junction solar cell with 500 nm i-layer thickness deviced by Ag back-electrode. With the 100 nm thick ultrathin top cell, a total conversion efficiency as high as 21.0% has been achieved on a-Si//poly-Si four-terminal tandem solar cells.