posted on 2022-04-19, 16:12authored byLuke McClintock, Ziyi Song, H. Clark Travaglini, R. Tugrul Senger, Vigneshwaran Chandrasekaran, Han Htoon, Dmitry Yarotski, Dong Yu
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) microribbons via spectrally, spatially, and temporally
resolved photocurrent and photoluminescence measurements. Distinct
peaks in the photocurrent spectra unambiguously confirm exciton formation
and allow for accurate extraction of the low temperature exciton binding
energy (39 meV). Photocurrent decays within a few μm at room
temperature, while a gate-tunable long-range photocurrent component
appears at lower temperatures (about 100 μm below 140 K). Carrier
lifetimes of 1.2 μs or shorter exclude the possibility of the
long decay length arising from slow trapped-carrier hopping. Free
carrier diffusion is also an unlikely source of the highly nonlocal
photocurrent, due to their small fraction at low temperatures. We
attribute the long-distance transport to high-mobility excitons, which
may open up new opportunities for novel exciton-based photovoltaic
applications.