Recombination and Resistive Losses in Amorphous Silicon / Crystalline Silicon Heterojunction Solar Cells

Abstract

ABSTRACTThis contribution investigates the electronic properties of a-Si:H/c-Si solar cells and explains their electrical output parameters open circuit voltage, short circuit current, and fill factor. Our device analysis is based on measurements of the internal quantum efficiency, of current/voltage and capacitance/voltage curves. We find carrier recombination within the crystalline silicon absorber material to be responsible for the limitation of the open circuit voltage. The short circuit current is restricted by collection losses in the absorber material and by absorption in the electrically inactive a-Si:H emitter. Resistive losses affecting the fill factor originate from the transport of minority carriers across the interface. The I/V curves measured at low temperatures reveal a characteristic S-shaped behavior. This effect increases with decrasing temperature and stems from the minority carrier transport, which is hindered by the band offset between a-Si:H and c-Si. We propose a new analytical model to describe this anomalous behavior.