Single-source, solvent-free, room temperature deposition of black $\gamma$-CsSnI$_3$ films

TL;DR

This paper introduces a solvent-free, room-temperature laser ablation method to deposit high-quality black $\gamma$ ext{-}CsSnI$_3$ films, overcoming previous obstacles related to phase stability and oxidation, advancing perovskite optoelectronic applications.

Contribution

It demonstrates a novel, solvent-free laser ablation technique for depositing stable, optically active $\gamma$ ext{-}CsSnI$_3$ films at room temperature, enabling scalable fabrication of lead-free halide perovskites.

Findings

Films exhibit a 1.32 eV band gap and near-infrared photoluminescence.

X-ray diffraction confirms orthorhombic $\gamma$ ext{-}phase formation.

Thermal stability maintained with Al$_2$O$_3$ capping layer.

Abstract

The presence of a non-optically active polymorph (yellow-phase) competing with the optically active polymorph (black $\gamma$-phase) at room temperature in CsSnI3 and the susceptibility of Sn to oxidation, represent two of the biggest obstacles for the exploitation of CsSnI3 in optoelectronic devices. Here room-temperature single-source in vacuum deposition of smooth black $\gamma$ - CsSnI3 thin films is reported. This has been done by fabricating a solid target by completely solvent-free mixing of CsI and SnI2 powders and isostatic pressing. By controlled laser ablation of the solid target on an arbitrary substrate at room temperature, the formation of CsSnI3 thin films with optimal optical properties is demonstrated. The films present a band gap of 1.32 eV, a sharp absorption edge and near-infrared photoluminescence emission. These properties and X-ray diffraction of the thin films confirmed the formation of the orthorhombic (B-$\gamma$) perovskite phase. The thermal stability of the phase was ensured by applying in situ an Al2O$_3$ capping layer. This work demonstrates the potential of pulsed laser deposition as a volatility-insensitive single-source growth technique of halide perovskites and represents a critical step forward in the development and future scalability of inorganic lead-free halide perovskites.