Optimization of mu c-Si1-xGex:H Single-Junction Solar Cells with Enhanced Spectral Response and Improved Film Quality

Abstract

Effects of RF power on optical, electrical, and structural properties of mu c-Si1-xGex:H films was reported. Raman and FTIR spectra from mu c-Si1-xGex:H films reflected the variation in microstructure and bonding configuration. Unlike increasing the germane concentration for Ge incorporation, low RF power enhanced Ge incorporation efficiency in mu c-Si1-xGex:H alloy. By decreasing RF power from 100 to 50 W at a fixed reactant gas ratio, the optical bandgap of mu c-Si1-xGex:H was reduced owing to the increase in Ge content from 11.2 to 23.8 at.%, while Ge-related defects and amorphous phase were increased. Consequently, photo conductivity of 1.62 x 10(-5) S/cm was obtained for the mu c-Si1-xGex:H film deposited at 60 W. By applying 0.9 mu m thick mu c-Si1-xGex:H absorber with X-C of 48% and [Ge] of 16.4 at.% in the single-junction cell, efficiency of 6.18% was obtained. The long-wavelength response of mu c-Si1-xGex:H cell was significantly enhanced compared with the mu c-Si:H cell. In the case of tandem cells, 0.24 mu m a-Si:H/0.9 mu m mu c-Si1-xGex:H tandem cell exhibited a comparable spectral response as 0.24 mu m a-Si:H/1.4 mu m mu c-Si:H tandem cell and achieved an efficiency of 9.44%.