Long-Range Self-Trapped Exciton Diffusion in Two-Dimensional Perovskites

Self-trapped excitons are usually formed in materials with soft lattice and strong carrier-phonon interaction, which exhibit a broadband emission with a large Stokes shift and high photoluminescence quantum yield, thereby showing promising applications in white light-emitting applications. Exciton diffusion plays a critical role in the luminous efficiency and color purity of light-emitting devices. Nevertheless, self-trapped excitons are essentially localized excitons and the study of self-trapped exciton diffusion remains elusive. Herein, we report an unexpected long diffusion length of 667 nm for self-trapped excitons in (PEA)2PbI4 at room temperature, significantly exceeding that of free excitons. This exceptional long-range diffusion is primarily attributed to the long lifetime of self-trapped excitons (∼16 ns) and photon recycling. Notably, although self-trapped excitons do not directly participate in photon recycling, we demonstrate that photon recycling, mediated by free excitons, can extend the diffusion length of self-trapped excitons by approximately 122 nm. These findings establish the feasibility of long-range exciton diffusion via energy transfer in nanostructures such as quantum dots and quantum wells.