Reduced defect density at the CZTSSe/CdS interface by atomic layer deposition of Al2O3

The greatest challenge for improving the power conversion efficiency of Cu2ZnSn(S,Se)(4) (CZTSSe)/CdS/ZnO thin film solar cells is increasing the open circuit voltage (V-OC). Probable leading causes of the V-OC deficit in state-of-the-art CZTSSe devices have been identified as bulk recombination, band tails, and the intertwined effects of CZTSSe/CdS hand offset, interface defects, and interface recombination. In this work, we demonstrate the modification of the CZTSSe absorber/CdS buffer interface following the deposition of 1 nm-thick Al2O3 layers by atomic layer deposition (ALD) near room temperature. Capacitance-voltage profiling and quantum efficiency measurements reveal that ALD-Al2O3 interface modification reduces the density of acceptor-like states at the heterojunction resulting in reduced interface recombination and wider depletion width. Indications of increased V-OC resulting from the modification of the heterojunction interface as a result of ALD-Al2O3 treatment are presented, These results, while not conclusive for application to state-of-the-art high efficiency CZTSSe devices, suggest the need for further studies as it is probable that interface recombination contributes to reduced V-OC even in such devices. Published by AIP Publishing.