Optimization of a-Si1-xGex:H single-junction and a-Si:H/a-Si1-xGex:H tandem solar cells with enhanced optical management

Abstract

This work aimed at improving the optical management of a-Si: H/a-Si1-xGex:H tandem cells and a-Si1-xGex:H single-junction cells. To improve the optical management, the effects of the a-Si1-xGex:H bandgap, the bandgap graded absorber and the n-type mu c-SiOx:H back reflecting layer on the cell performance were investigated. Optical reflection spectra, internal quantum efficiency, external quantum efficiency (EQE), and cell performance were used to evaluate the improvement of the optical properties of solar cells. The tandem cells with a-Si1-xGex:H bandgap of 1.53 eV exhibited sufficient optical absorption from 630 to 900 nm and thus lead to higher J(SC). Second, the EQE of a-Si1-xGex:H single-junction cell was significantly enhanced from 630 to 720 nm by employing bandgap graded absorber that relatively improved the J(SC) by 3.8% despite that the reduction in EQE from 720 to 900 nm compared to the cell without bandgap grading. Moreover, the mu c-SiOx:H(n)/Ag back reflector showed higher optical reflection than a-Si:H(n)/Ag did, which relatively improved the J(SC) by 12.3%. The cell with mu c-SiOx:H(n)/Ag back reflector exhibited a comparable J(SC) and efficiency to the cell with ITO-Ag. The previously mentioned approaches are relevant to enhance the optical management in cells and can be applied to silicon-based thin-film solar cells.