Highly Mobile Excitons in Single Crystal Methylammonium Lead Tribromide Perovskite Microribbons*

Excitons are often given negative connotation in solar energy harvesting in part due to their presumed short diffusion lengths. We investigate exciton transport in single-crystal methylammonium lead tribromide (MAPbBr3) nanoribbons via spectrally, spatially, and temporally resolved photocurrent and photoluminescence measurements. Distinct peaks in the photocurrent spectra confirm exciton formation and allow for accurate extraction of the low temperature exciton binding energy (39 meV). Photocurrent decays within a few um at room temperature, while a long-range photocurrent component appears at lower temperatures (100 um below 140 K). Carrier lifetimes of 1.2 us or shorter exclude the possibility of the long decay length arising from slow trapped-carrier hopping. We attribute the long-distance transport to high-mobility excitons. The observation of high-mobility excitons in halide perovskites implies exciton transport does not limit the energy conversion process and may open up new opportunities for novel exciton-based photovoltaic applications.