Photovoltaic Characteristics of Ultra-Thin Silicon Solar Cells below 10 nm

Abstract

Silicon nanowall solar cells are expected to exceed the efficiency limit of bulk Si solar cells owing to quantum confined enlarged bandgap with optical absorption properties. However, one of the concerns of nanowall cells is the presence of surface states to increase the recombination velocity. In this work, photovoltaic (PV) properties of ultra-thin lateral p+-i-n+ Si solar cells with Si layer thickness below 10 nm have been characterized under AM1.5 light illumination, and the impact of thickness on PV characteristics has been examined. With thinner Si layer less than 6 nm, open-circuit voltage (VOC) has shown gradual increment, which is predicted by theoretical calculation of bandgap enlargement. The short-circuit current (ISC) has shown linear dependency on thickness from 3.3 to 7.6 nm, which indicates that generated photocurrent is linearly proportional to volume of Si layer. However, the gradual current reduction with anode voltage application caused the FF degradation. This is mainly caused by series resistance due to missing dopants. Therefore, formation of junctions is a critical issue for ultra-thin Si solar cells.