Light-Induced Lattice Coherence and Emission Enhancement in PTM-Passivated CsSnI3 Perovskites

TL;DR

This study demonstrates that PTM passivation significantly enhances the optical stability and emission efficiency of CsSnI3 perovskites, revealing light-induced lattice coherence and dynamic carrier behaviors.

Contribution

It introduces PTM passivation as a method to improve stability and optical performance in CsSnI3 perovskites, highlighting light-induced lattice reordering and carrier dynamics.

Findings

Up to tenfold increase in photoluminescence quantum yield with PTM passivation.

Reversible sharpening of low-frequency Raman mode indicating lattice reordering.

Distinct carrier relaxation behaviors in microcrystals and nanocrystals.

Abstract

Metal halide perovskites continue to lead in optoelectronic applications, but the toxicity of lead has driven efforts to identify environmentally benign alternatives. Cesium tin iodide is one such, with a direct bandgap and near-infrared emission, though its performance is limited by instability. We show that phthalimide (PTM) passivation during single crystal growth enhances optical output and ambient stability. Under continuous excitation, PTM-passivated microscale crystals show up to a nearly one order of magnitude increase in photoluminescence (PL) quantum yield, accompanied by reversible sharpening of a low-frequency Raman mode associated with Cs rattling. This reveals dynamic, light-induced lattice reordering that passivates trap states and enhances radiative recombination. Mechanical grinding yields nanocrystals with redshifted, narrowed PL, consistent with a relaxed polymorph and reduced inhomogeneous broadening. Despite increased surface area, PTM remains effective in preserving near-infrared emission in nanocrystals as well. Power-dependent PL reveals distinct carrier dynamics, where microcrystals show redshift due to bandgap renormalization, while nanocrystals show blueshift and elevated carrier temperatures (300 to 1900 K), consistent with hot-carrier recombination. Extended illumination reveals reversible optical changes, including PL modulation, reflecting dynamic light-matter interactions and evolving defect landscapes. These results identify PTM-passivated Cesium tin iodide as an ideal platform for probing morphology-dependent carrier relaxation and light-induced vibrational coherence in lead-free perovskites.