Close‐Spaced Sublimation of CdCl <sub>2</sub> Enables Uniform CdS Thin Films for Certified 8.08%‐Efficient Sb <sub>2</sub> S <sub>3</sub> Solar Cells
Yuqian Huang, Lin Feng, Jie Yang, Haolin Wang, Zhen Yu, Hongling Guo, Yongtai Yin, Huanhuan Zhang, Zhixinke Li, Jingyi Yan, Jiangfeng Liu, Tao Chen, Gang Wang
Abstract
ABSTRACT CdCl 2 treatment has emerged as a transformative protocol for augmenting the crystallinity and electrical performance of CdS thin films, representing a foundational advancement in the development of high‐efficiency CdTe and Sb 2 (S,Se) 3 solar cells. However, the conventional spin‐coating method causes inhomogeneous deposition of CdCl 2 on the surface of CdS films, resulting in vastly different CdS(solid)–CdCl 2 (solid) and CdS(solid)–CdCl 2 (vapor) reaction modes during annealing. This process activates pinhole or crack formation and causes grain inhomogeneity due to the CdS(solid)–CdCl 2 (solid) faster reaction rate, deleteriously impacting the device performance through compromised carrier extraction and enhanced interfacial recombination. This study introduces a close‐spaced sublimation (CSS) approach for uniform CdCl 2 vapor treatment of CdS films. This methodology disrupts the inhomogeneous growth paradigm, enabling the conformal deposition of ultrathin CdS layers (∼20 nm) on FTO/TiO 2 substrates. The optimized CdS thin films demonstrated enhanced charge extraction efficiency and suppressed interfacial recombination—evidence of improved carrier transport kinetics. Under AM 1.5G illumination, the best Sb 2 S 3 solar cell fabricated through this strategy delivered a record power conversion efficiency of 8.30% (certified 8.08%). The CSS technique, which enables controlled homogeneous crystallization, establishes a paradigm for realizing high‐quality CdS films and is an essential breakthrough for high‐efficiency Sb 2 (S,Se) 3 and CdTe photovoltaic devices.