Bandlike Transport and Charge-Carrier Dynamics in BiOI Films

Following the emergence of lead halide perovskites (LHPs)as materialsfor efficient solar cells, research has progressed to explore stable,abundant, and nontoxic alternatives. However, the performance of suchlead-free perovskite-inspired materials (PIMs) still lags significantlybehind that of their LHP counterparts. For bismuth-based PIMs, onesignificant reason is a frequently observed ultrafast charge-carrierlocalization (or self-trapping), which imposes a fundamental limiton long-range mobility. Here we report the terahertz (THz) photoconductivitydynamics in thin films of BiOI and demonstrate a lack of such self-trapping,with good charge-carrier mobility, reaching & SIM;3 cm(2) V-1 s(-1) at 295 K and increasinggradually to & SIM;13 cm(2) V-1 s(-1) at 5 K, indicative of prevailing bandlike transport.Using a combination of transient photoluminescence and THz- and microwave-conductivityspectroscopy, we further investigate charge-carrier recombinationprocesses, revealing charge-specific trapping of electrons at defectsin BiOI over nanoseconds and low bimolecular band-to-band recombination.Subject to the development of passivation protocols, BiOI thus emergesas a superior light-harvesting semiconductor among the family of bismuth-basedsemiconductors.