Improved Open‐Circuit Voltage of Sb2Se3 Thin‐Film Solar Cells Via Interfacial Sulfur Diffusion‐Induced Gradient Bandgap Engineering

Abstract

The performance of thermally deposited Sb2Se3 solar cells are severely limited by various bulk and interfacial recombination, instigating a large open‐circuit voltage (VOC) deficit. Ternary Sb2(S,Se)3 is considered as a remedy, however, it is also subjected to a dilemma that improvement in VOC will be escorted by JSC loss due to the shrinkage of light harvest. Thus, a gradient of S/Se across the film is a prerequisite to avoid this detrimental compromise. Herein, the incorporation of S in the Sb2Se3 absorber layer evaporated from a CdS buffer layer during vapor transport deposition (VTD) process, and its further self‐activated diffusion at the interface upon ambient storage is explored. For the gradient indium tin oxide (ITO)/CdS/Sb2(S,Se)3/Sb2Se3/Au solar cell, the large bandgap Sb2(S,Se)3 at the heterojunction side contributes to high VOC, while the narrow bandgap Sb2Se3 at the top side confirms high JSC. Sulfur diffusion at the CdS/Sb2Se3 interface also improves the junction quality with an enlarged Vbi, reduced interfacial defects and recombination loss, thus improving VOC from 393 to 430 mV. Such VOC represents the highest value for that of thermally deposited Sb2Se3 solar cells. The champion device also delivers an interesting efficiency of 7.49%. This research provides substantial guidance in exploring efficient approaches to improve the performance of Sb2Se3 solar cells.