Impact of Surface Band Bending at the Rear Si–SiO2 Interface on Conversion Efficiency of Rear Locally-Contacted Silicon Solar Cells

Abstract

The dependence of the conversion efficiency of rear locally-contacted p-type silicon solar cells on surface band bending at the rear Si–SiO2 interface is studied for several substrate resistivities and rear oxide thicknesses through two-dimensional device simulations. Conventionally, the cell efficiency was thought to increase as the band bending induced by work function difference and positive oxide charge increases. However, this is not necessarily true. Under the assumption of asymmetrical capture cross sections (σn/σp=102 at midgap) at the rear interface, the cell efficiency has a maximum value and then decreases gradually as the band bending increases. This is because a large number of generated electrons (minority carriers) are pulled into the rear surface and the greater part of the accumulated electrons flow into the rear p+-contact for large band bending.