Improvement of a-Si:H and nc-Si:H multi-junction solar cells by optimization of textured back reflectors

The effect of the texture of Ag/ZnO back reflector (BR) on nc-Si:H single-junction solar cell performance has been investigated systematically. Using a high textured BR, a 74% gain in short circuit current density (J_sc) was obtained over a cell made using the same recipe on specular stainless steel. However, the texture reduced the fill factor (FF) from 0.73 to 0.54. Dark current versus voltage measurements showed a significant increase in reverse saturate current when the texture is increased, indicating a poor nc-Si:H material quality in the nc-Si:H cells deposited on highly textured Ag/ZnO BR. In order to maintain both high J_sc and FF, we have optimized the BR texture. With the improved BR, we have achieved initial efficiencies of 9.5% in a nc-Si:H single-junction and 13.4% in an a-Si:H/nc-Si:H/nc-Si:H triple-junction solar cells made at 10 ¿/s.