Doping and Distortions as Tools to Tune the Optoelectronic Properties of Halide Double Perovskites*

In recent times, halide double perovskites (HDP) have attracted considerable attention as promising optoelectronic materials. In a combined theoretical and experimental study, we propose a design strategy through doping and distortion which can lead to white light emission and long excited state lifetime in HDP. Taking the example of an inorganic compound Cs₂Ag(M, M′)Cl₆, where M and M′ are heavy sp-elements,  we discuss the results from first principles electronic structure calculations, empirical molecular-orbital picture, parity driven symmetry analysis to predict the tuning of optoelectronic phenomena in these materials. The theoretical results are corroborated through experimental evidences arising from far-infrared absorption, steady-state and time-resolved photoluminescence, bias-dependent photoluminescence measurements. The present study establishes the role of structural distortion modes in influencing the optoelectronic behavior in HDP.