Excited State Dynamics and Transport of Self-trapped Excitons in Lead-Free Double Perovskites

Understanding the excited state and transport dynamics of self-trapped excitons (STEs) in lead-free double perovskites (DPs) is essential for popularizing their optoelectronic applications. Herein, we apply a series of spectroscopies and microscopies techniques to systematically investigate the formation, transport, and relaxation dynamics of SETs in Bi-doped double perovskites (Bi-DPs). The PLQY, consistent with the STEs activation energy of Bi-DPs shows an increasing and then decreasing trend as a function of Bi³⁺ content, suggesting tiny Bi³⁺ can passive the defects and more Bi could generate more non-radiative decay channels. Moreover, we find the Bi-DPs exhibit dual white emission, originating from the intrinsic STEs (i-STE) and Bi³⁺ induced STEs (Bi-STEs), respectively. The STEs formation and relaxation timescale will be detailed discussed in as well. Finally, we will present the temperature-active transport behavior. The fundamental mechanism understanding of the doping engineering established in this work will provide helpful guidance about how to improve the performance of DPs optoelectronic devices.