Boosting near-infrared absorbance and exciton emission in perovskite-inspired Cs₃Sb₂I₉ through Sn doping

Antimony-based perovskite materials have emerged as promising alternatives to lead-based hybrids, but their wide bandgaps and weak photoluminescence (PL) emission hinder their applicability in optoelectronic devices. In this study, a strategic doping of tin (Sn) was employed to modulate the electronic structure of Cs₃Sb₂I₉. Sn doping induced a distinct redshift in the light absorption spectrum, with, to our knowledge, a new peak emerging around 1 eV, accompanied by an enhanced PL emission. First-principles density functional theory (DFT) calculations revealed that the bandgap narrowing results from the formation of an intermediate band. Further analysis combining phonon spectrum calculations with temperature-dependent Raman spectroscopy showed that Sn doping mitigates anharmonic effects, stabilizing the lattice and eliminating the influence of lattice distortion on defect emission. Additionally, doping facilitated an exciton–phonon coupling enhancement, leading to a marked increase in the efficiency of self-trapped emission (STE). These findings open, to our knowledge, new avenues for optimizing sunlight absorption in perovskite-inspired semiconductors, unlocking their potential for sustainable energy applications.