Improved Open‐Circuit Voltage of Sb<sub>2</sub>Se<sub>3</sub> Thin‐Film Solar Cells Via Interfacial Sulfur Diffusion‐Induced Gradient Bandgap Engineering
Shuo Chen, Muhammad Ishaq, Wei Xiong, Usman Ali Shah, Umar Farooq, Jingting Luo, Zhuanghao Zheng, Zhenghua Su, Ping Fan, Xianghua Zhang, Guangxing Liang
Abstract
The performance of thermally deposited Sb 2 Se 3 solar cells are severely limited by various bulk and interfacial recombination, instigating a large open‐circuit voltage ( V OC ) deficit. Ternary Sb 2 (S,Se) 3 is considered as a remedy, however, it is also subjected to a dilemma that improvement in V OC will be escorted by J SC 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 Sb 2 Se 3 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/Sb 2 (S,Se) 3 /Sb 2 Se 3 /Au solar cell, the large bandgap Sb 2 (S,Se) 3 at the heterojunction side contributes to high V OC , while the narrow bandgap Sb 2 Se 3 at the top side confirms high J SC . Sulfur diffusion at the CdS/Sb 2 Se 3 interface also improves the junction quality with an enlarged V bi , reduced interfacial defects and recombination loss, thus improving V OC from 393 to 430 mV. Such V OC represents the highest value for that of thermally deposited Sb 2 Se 3 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 Sb 2 Se 3 solar cells.