MAPbBr(3) and MAPbI(3) films cast onto glass slides and physically paired together undergo halide exchange to form mixed halide films. The change in halide composition in these two similar to 130 nm thick films occurs concurrently with Br- diffusing toward the MAPbI(3) film and I- diffusing toward the MAPbBr(3) film.
The diffusion of these halide species, which is tracked through changes in the absorption, offers a direct measurement of thermally activated halide diffusion in perovskite films. The increase in the rate constant of halide diffusion with increasing temperature (from 8.3 x 10(-6) s(-1) at 23 degrees C to 3.7 x 10(-4) s(-1) at 140 degrees C) follows an Arrhenius relationship with activation energy of 51 kJ/mol. The thermally activated halide exchange shows the challenges of employing layers of different metal halide perovskites in stable tandem solar cells.
Tor Elmelund, Rebecca A. Scheidt, Brian Seger and Prashant V. Kamat
ACS Energy Lett. 2019, 4, 8