Mussakhanuly, N.; Soufiani, A.M.; Bernardi, S.; Gan, J.; Bhattacharyya, S.K.; Chin, R.L.; Muhammad, H.; Dubajic, M.; Gentle, A.; Chen, W.; Zhang, M.; Nielsen, M.P.; Huang, S.; Asbury, J.; Widmer-Cooper, A.; Yun, J.S.; Hao, X.: Thermal Disorder-Induced Strain and Carrier Localization Activate Reverse Halide Segregation. Advanced Materials 36 (2024), p. 2311458/1-12
10.1002/adma.202311458
Open Access Version
Abstract:
The reversal of halide ions is studied under various conditions. However, the underlying mechanism of heat-induced reversal remains unclear. This work finds that dynamic disorder-induced localization of self-trapped polarons and thermal disorder-induced strain (TDIS) can be co-acting drivers of reverse segregation. Localization of polarons results in an order of magnitude decrease in excess carrier density (polaron population), causing a reduced impact of the light-induced strain (LIS – responsible for segregation) on the perovskite framework. Meanwhile, exposing the lattice to TDIS exceeding the LIS can eliminate the photoexcitation-induced strain gradient, as thermal fluctuations of the lattice can mask the LIS strain. Under continuous 0.1 W cm⁻2 illumination (upon segregation), the strain disorder is estimated to be 0.14%, while at 80 °C under dark conditions, the strain is 0.23%. However, in situ heating of the segregated film to 80 °C under continuous illumination (upon reversal) increases the total strain disorder to 0.25%, where TDIS is likely to have a dominant contribution. Therefore, the contribution of entropy to the system's free energy is likely to dominate, respectively. Various temperature-dependent in situ measurements and simulations further support the results. These findings highlight the importance of strain homogenization for designing stable perovskites under real-world operating conditions.