Photo-activated charge transport and exciton dynamics in Cs₂NaInCl₆ double perovskite

On account of their environmentally-benign composition and structural stability, lead-free halide double perovskites have drawn increasing attention. Even though the charge-transport behavior of Cs₂NaInCl₆, one of these perovskites, remains poorly understood under illumination, it shows strong self-trapped exciton (STE) emission. Through a combined optical and electrical approach, this work investigates the interplay between electrical transport and exciton dynamics. With a wide bandgap and intrinsic STE-mediated blue emission, a highly crystalline cubic phase is confirmed by the optical and structural analyses. Multi-timescale photoinduced relaxation dynamics associated with recombination processes, lattice relaxation and exciton localization are inferred primarily from TRPL measurements and qualitatively supported by complementary transient absorption observations. Current-voltage measurements, dielectric analysis and complementary impedance spectroscopy evidence that illumination significantly reduces bulk resistance, enhances dielectric polarization and induces persistent photoconductivity. While the optical response is governed by STEs, the results indicate that photo-generated carriers dominate charge transport with an indirect influence of exciton dynamics through trap-state modulation. New insight into the optoelectronic functionality of lead-free double perovskites is provided through a physically-consistent framework proposed to correlate macroscopic transport properties with microscopic excitonic behavior.