Excited State Dynamics and Transport of Self-Trapped Excitons in Bi-Doped Cs₂Na0.4Ag0.6In(1–y)BiyCl₆ Double Perovskites

Lead-free double perovskites (DPs) have become notable in white light emission applications due to the self-trapped exciton (STE) formation in the excited state. However, the mechanism understanding of the excited state dynamics and transport of STE remains ambiguous. Here, we demonstrate a new STE (Bi-STE) forming in tiny Bi-doped Cs2Na0.4Ag0.6InCl6, alongside its intrinsic STE (i-STE), resulting in the DPs photoluminescence quantum yield (PLQY) increasing to as high as >90%. The i-STE exhibits faster formation (60 fs) and slower relaxation dynamics (2.8 μs) compared to the Bi-STE. Moreover, we unveil that the Bi doping can augment the i-STE diffusion properties to attain a diffusion coefficient (diffusion length) of 0.012 cm2 s-1 (1.7 μm) at room temperature, indicating their promise in photovoltaic applications. Our results shed light on significant STE dynamics and transport mechanisms in DPs, providing a new roadmap for advancing existing and crafting new DPs in light emission applications.