Improving the open-circuit voltage of Cu2ZnSnSe4 thin film solar cells via interface passivation

Abstract

This study reports on substantial improvement of the open-circuit voltage (V-oc) of Cu2ZnSnSe4 (CZTSe) thin film solar cells by applying a passivation strategy to both the top and bottom interfaces of the CZTSe absorber, which involves insertion of a thin dielectric layer between the CZTSe and the surrounding layers. The study also presents in-depth material characterizations using transmission electron microscopy, energy dispersive X-ray spectroscopy, low-temperature photoluminescence, and secondary ion mass spectrometry, to reveal the effects of the interface passivation. To passivate the bottom Mo/CZTSe interface, a dielectric layer with patterned local contacts of dimensions down to similar to 100nm was prepared using nanosphere lithography. With this, the V-oc, short-circuit current, and fill factor (FF) were significantly enhanced due to reduction in carrier recombination at the bottom Mo/CZTSe interface. The top CZTSe/CdS interface was passivated by a thin dielectric layer which prevented inter-diffusion of Cd and Cu at the top interface, thereby improving the junction quality. Application of the top passivation layers resulted in substantial improvement in V-oc and FF, thereby achieving the V-oc deficit of 0.542V which is the record value among reported CZTSe solar cells. Copyright (c) 2017 John Wiley & Sons, Ltd.