Lead-Free Potassium Alloyed Cs2AgBiBr6: Tunable Optoelectronic Properties and Carrier-Lattice Interaction

Abstract

The role of the carrier-lattice interaction and associated self-trapped excitons (STEs) in broadband white-light emission in perovskite halides is one of the key aspects when aiming to develop next generation semiconductors for lighting applications. Herein, we provide microscopic insight on optoelectronic properties and electron–phonon interactions in potassium (K+) alloyed Cs2AgBiBr6, while evaluating its potential as a single material tunable light emitter. While K+ partially occupying the Cs+ site leads to blue-light emission at low K+ ion concentrations, a sudden photoluminescence broadening and white-light emission occur at relatively higher alloying concentrations where K+ starts to occupy Ag+ sites. Simulation reveals an anomalous increase in carrier lattice coupling strength (via the Fröhlich mechanism) when K+ replaces Ag+. This along with the increased density of STEs (aided by strong electron–phonon coupling and more octahedral distortion) and induced free exciton (FE) emission is proposed to play a major role behind the observed photoluminescence (PL) broadening and white-light emission. This study should stimulate further research on single material based white-light emitters for next generation solid-state lighting applications.