Solution-Processed ZnxCd1-xS Buffer Layers for Vapor Transport-Deposited SnS Thin-Film Solar Cells: Achieving High Open-Circuit Voltage.

As an alternative buffer material to CdS, ZnxCd1-xS buffer layers for vapor transport-deposited SnS thin-film solar cells (TFSCs) were fabricated using the successive ionic layer adsorption and reaction (SILAR) method. Varying the Zn-to-Cd ratio resulted in a series of ZnxCd1-xS thin films with controllable band gaps in the range of 2.40-3.65 eV. The influence of the Zn-to-Cd ratio on the cell performance was investigated in detail. The Zn0.34Cd0.66S buffer layer was found to be the optimal composition for SnS TFSCs, and a record open-circuit voltage (Voc) of 0.405 V was achieved with an efficiency of 3.72%, whereas the SILAR-CdS buffer layer rendered a Voc of 0.324 V. The improvement in Voc when using the Zn0.34Cd0.66S buffer layer was corroborated by the spike-type conduction band offset of 0.35 eV with the SnS absorber, as revealed by the X-ray photoelectron spectroscopy analysis. In addition, minimized interfacial recombination at the SnS/Zn0.34Cd0.66S heterojunction was confirmed by the temperature-dependent Voc analysis under illuminated conditions.