Self-trapped exciton diffusion in a lead-free two-dimensional hybrid perovskite

We report the first observation of diffusive self-trapped exciton (STE) transport in a lead-free two-dimensional hybrid perovskite-like [CMA]4[Bi2Cl10], where [CMA] is cyclohexylmethylam. The material exhibits broadband photoluminescence from self-trapped states, combined with unexpectedly long exciton diffusion lengths exceeding 1µm. Using time- and spatially resolved spectroscopy, we determine diffusion coefficients on the order of 0.1 cm²/s. The thermally assisted STE mobility challenges conventional understanding and offers promising opportunities for broadband emitters, sensors, and light-harvesting devices. Our findings provide new insights into exciton dynamics in soft halide lattices and open pathways to tailored excitonic transport in low-dimensional perovskites.