Low-Temperature Plasma-Enhanced Atomic Layer Deposition of ZnMgO for Efficient CZTS Solar Cells

Cu2ZnSnS4 (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 degrees 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 VOC 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 JSC value and boosting the efficiency to 10%.

Automated summary

Cu2ZnSnS4 (CZTS) solar cells are promising due to their abundance, dry processability, and environmental friendliness. This study demonstrates the deposition of a ZnMgO window layer using atomic layer deposition (ALD), which exhibits superior smoothness and suitable doping density. The optimized ZnMgO layer reduces charge carrier recombination and parasitic absorption, leading to improved voltage and current characteristics of the CZTS solar cell, with an efficiency of 10%.