Precursor Chemistry Governing Morphology and Cation Disorder in AgBiS 2 Solar Absorber for Photoelectrochemical Water Splitting

Abstract

AgBiS 2 has emerged as a highly promising light-absorbing material for solar energy conversion owing to its direct band gap, strong visible-light absorption, and compatibility with scalable solution-based processing. A particularly intriguing characteristic of AgBiS 2 is that its optical absorption coefficient can be markedly enhanced through cation-disorder engineering.Previous studies have demonstrated that solution chemistry can induce cation disorder in AgBiS 2 ; however, it simultaneously governs crystal growth and morphology, including the formation of one-dimensional nanostructures. Despite its importance, the interplay between cation disorder and morphology control has remained poorly understood. Here, we systematically investigate the chemical interactions among thiourea (TU), serving as both a sulfur (S) source and coordinating ligand, metal cations (Ag + and Bi 3+ ), and dimethyl sulfoxide (DMSO) as the solvent. Density-functional-theory calculations combined with spectroscopic and structural analyses consistently reveal that both TU and DMSO bind more strongly to Bi 3+ than to Ag⁺. Notably, the comparable binding energies of the TU-Bi and DMSO-Bi complexes impose a thermodynamic constraint on cation disorder. Consequently, increasing the TU concentration suppresses cation disorder, while instead promoting anisotropic crystal growth, leading to the formation of one-dimensional AgBiS 2 nanostructures through specific TU-metal coordination. Furthermore, AgBiS 2 thin-film photocathodes with controlled nanostructures were fabricated and evaluated for photoelectrochemical (PEC) water splitting, demonstrating how the chemically driven trade-off between cation disorder and morphology directly influences PEC performance.