Low-Temperature Plasma-Enhanced Atomic Layer Deposition of ZnMgO for Efficient CZTS Solar Cells
Xin Cui, Kaiwen Sun, Jialiang Huang, Heng Sun, Ao Wang, Xiaojie Yuan, Martin A. Green, Bram Hoex, Xiaojing Hao
Abstract
Cu 2 ZnSnS 4 (CZTS) solar cells are an emerging photovoltaic technology owing to their earth abundance, all-dry processability, and environmental friendliness. Further power conversion efficiency enhancement of the Cd-free CZTS device necessitates the substitution of traditionally used intrinsic ZnO by an alternative wide-band-gap window layer. Here, we demonstrate deposition of a ZnMgO window layer of controlled thickness, composition, and electro-optical properties by atomic layer deposition (ALD). The amorphous ZnMgO deposited at low temperature down to 100 °C using plasma-enhanced ALD showed smoothness superior to that of high-temperature plasma-enhanced ALD and doping density comparable to that of high-temperature thermal ALD but with a much lower electron affinity. The overall charge carrier recombination at the CZTS/ZnSnO/ZnMgO region was reduced due to the optimized ZnMgO conduction band minimum, thus reducing the V OC value and fill factor loss for a CZTS solar cell. In addition, the thinner- and larger-band-gap ZnMgO was believed to reduce the parasitic absorption, improving the J SC value and boosting the efficiency to 10%.