Cs2AgxNa1−xBiyIn1−yCl6 perovskites approaching photoluminescence quantum yields of 100%

Abstract

A new single-step and green approach for the synthesis of microcrystalline Cs₂Ag_xNa_1−xBi_yIn_1−yCl₆ (CANBIC) perovskites in ambient conditions is introduced. The CANBIC powders emit broadband self-trapped excitonic photoluminescence (PL) with a champion PL quantum yield (QY) of 98 ± 2% and a PL lifetime of ca. 2 μs observed for x = 0.40 and y = 0.01–0.02. The study focuses on the dependence of structural, spectral, and photophysical properties of CANBICs on Bi content. CANBICs are solid solutions with isomorphous In-to-Bi substitution with the bandgap and valence band edge energy decreasing gradually with increasing y. The PL QY and the rate constant of the radiative recombination showed volcano-shaped dependences on the Bi content, while the rate of the non-radiative recombination revealed a drastic growth by three orders of magnitude as the Bi fraction y was elevated from 0.01 to 1.0 indicating that BiCl₆ units are responsible for non-radiative recombination.