Oxygenated CdS Buffer Layers Enabling High Open-Circuit Voltages in Earth-Abundant Cu2BaSnS4 Thin-Film Solar Cells

Earth-abundant Cu2BaSnS4 (CBTS) thin films exhibit a wide bandgap of 2.04-2.07 eV, a high absorption coefficient > 10(4) cm(-1), and a p-type conductivity, suitable as a top-cell absorber in tandem solar cell devices. In this work, sputtered oxygenated CdS (CdS: O) buffer layers are demonstrated to create a good p-n diode with CBTS and enable high open-circuit voltages of 0.9-1.1 V by minimizing interface recombination. The best power conversion efficiency of 2.03% is reached under AM 1.5G illumination based on the configuration of fluorine-doped SnO2 (back contact)/CBTS/CdS: O/CdS/ZnO/aluminumdoped ZnO (front contact).