Interplay between Cation "Coloring" and Stereochemically Active Lone Pairs in AgBiS2 Thin Films
Kristopher M Koskela1, Anindya Pakhira2, Marissa J Strumolo1
1Department of Chemistry, University of Southern California, Los Angeles, California 90089-3502, United States.
Abstract:
Solution-processed AgBiS2 thin films were fabricated using novel thiol-amine precursor inks to investigate the stereochemical activity of Bi3+ 6s2 lone pairs and their impact on the structure. A dual-space analysis combining Bragg diffraction and hard X-ray photoelectron spectroscopy (HAXPES) revealed a rock salt-like average structure with local distortions linked to cation coloring. Density functional theory (DFT) and crystal orbital Hamilton population (COHP) analyses confirmed that local Bi-rich and Ag-rich nanodomains amplify stereochemical activity, whereas more mixed and cation-order nanodomains are less stereochemically active. This local, nanoscopic mixing of segregated and ordered domains would indeed explain an average Fm3̅m structure that is rock salt-like and that does not manifest the full anharmonicity and noncentrosymmetry evidenced in canonical structures with stereochemical expression. These findings provide insights into the local structural and electronic complexities governing the optoelectronic properties of AgBiS2 thin films.
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