posted on 2019-12-10, 18:41authored byCamille Stavrakas, Géraud Delport, Ayan A. Zhumekenov, Miguel Anaya, Rosemonde Chahbazian, Osman M. Bakr, Edward S. Barnard, Samuel D. Stranks
Halide perovskites have shown great potential for light
emission
and photovoltaic applications due to their remarkable electronic properties.
Although the device performances are promising, they are still limited
by microscale heterogeneities in their photophysical properties. Here,
we study the impact of these heterogeneities on the diffusion of charge
carriers, which are processes crucial for efficient collection of
charges in light-harvesting devices. A photoluminescence tomography
technique is developed in a confocal microscope using one- and two-photon
excitation to distinguish between local surface and bulk diffusion
of charge carriers in methylammonium lead bromide single crystals.
We observe a large dispersion of local diffusion coefficients with
values between 0.3 and 2 cm2·s–1 depending on the trap density and the morphological environmenta
distribution that would be missed from analogous macroscopic or surface
measurements. This work reveals a new framework to understand diffusion
pathways, which are extremely sensitive to local properties and buried
defects.