Thermodynamically Stable Orthorhombic γ-CsPbI 3 Thin Films for High-Performance Photovoltaics

• Published in: Journal of the American Chemical Society Vol. 140; no. 37; pp. 11716 - 11725
• Main Authors: Zhao, Boya, Jin, Shi-Feng, Huang, Sheng, Liu, Ning, Ma, Jing-Yuan, Xue, Ding-Jiang, Han, Qiwei, Ding, Jie, Ge, Qian-Qing, Feng, Yaqing, Hu, Jin-Song
• Format: Journal Article
• Language: English
• Published: United States 19.09.2018
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.8b06050

All-inorganic lead halide perovskites demonstrate improved thermal stability over the organic-inorganic halide perovskites, but the cubic α-CsPbI with the most appropriate bandgap for light harvesting is not structurally stable at room temperature and spontaneously transforms into the undesired orthorhombic δ-CsPbI . Here, we present a new member of black-phase thin films of all-inorganic perovskites for high-efficiency photovoltaics, the orthorhombic γ-CsPbI thin films with intrinsic thermodynamic stability and ideal electronic structure. Exempt from introducing organic ligands or incorporating mixed cations/anions into the crystal lattice, we stabilize the γ-CsPbI thin films by a simple solution process in which a small amount of H O manipulates the size-dependent phase formation through a proton transfer reaction. Theoretical calculations coupled with experiments show that γ-CsPbI with a lower surface free energy becomes thermodynamically preferred over δ-CsPbI at surface areas greater than 8600 m /mol and exhibits comparable optoelectronic properties to α-CsPbI . Consequently, γ-CsPbI -based solar cells display a highly reproducible efficiency of 11.3%, among the highest records for CsPbI thin-film solar cells, with robust stability in ambient atmosphere for months and continuous operating conditions for hours. Our study provides a novel and fundamental perspective to overcome the Achilles' heel of the inorganic lead iodide perovskite and opens it up for high-performance optoelectronic devices.