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.