Computational Screening and Discovery of Silver-Indium Halide Double Salts

TL;DR

This study uses computational methods to design and analyze silver-indium halide double salts, predicting their stability, electronic properties, and potential applications despite synthesis challenges.

Contribution

It introduces a novel lead-free halide compound, AgInI4, and explores the broader phase space of Ag-In-I compounds for optoelectronic uses.

Findings

AgInI4 is predicted to be stable with a 1.72 eV band gap.

Multiple stable and metastable phases with different structures and band gaps identified.

Experimental synthesis of AgInI4 remains unsuccessful despite computational predictions.

Abstract

Perovskite-inspired materials have emerged as promising candidates for both outdoor and indoor photovoltaic applications owing to their favorable optoelectronic properties and reduced toxicity. Here, we employ the experimentally realized AgBiI$_4$ double salt as a structural prototype and replace Bi$^{3+}$ with In$^{3+}$ to design a novel lead-free halide compound, AgInI$_4$. First-principles calculations predict that AgInI$_4$ is both chemically and dynamically stable, exhibiting a direct band gap of 1.72 eV, comparable to its bismuth analogue. However, its predicted photovoltaic performance, evaluated using the spectroscopic limited maximum efficiency metric, is lower under both solar and LED illumination. This reduction arises primarily from symmetry-forbidden optical transitions and the absence of Bi-derived 6s$^2$ lone-pair states at the valence band maximum. High-throughput screening of the Ag-In-I ternary phase-space reveals several more stable and metastable compounds that fall into two structural families: tetrahedrally and octahedrally coordinated, with characteristic band gaps near 3.0 eV and 2.0 eV, respectively. Despite multiple synthetic attempts, the predicted AgInI$_4$ phase could not be experimentally realized, underscoring the challenges of stabilizing indium-based halide double salts. While these materials are unlikely to serve as efficient photovoltaic absorbers, their tunable band gaps and stability make them promising candidates for charge transport and other optoelectronic applications.