Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
DOI: https://doi.org/10.29363/nanoge.hopv.2022.178
Publication date: 20th April 2022
The compositional stability of mixed halide perovskite semi-conductors is limited by the light or electrical bias induced phase segregation. To identify the mechanism and cause of the light-induced phase-segregation phenomena (photo-segregation), we investigated the full compositional range of MAPb(BrxI1-x)3 with x = 0…1, by simultaneous in-situ X-ray diffraction and photoluminescence spectroscopy during illumination. This multimodal approach allows us to quantify the halide redistribution, its kinetics as well as the corresponding charge carrier distribution, in-situ during segregation. We apply previously derived thermodynamic models directly to rationalize the experimental data.[1,2] We find that gap-models (by Kuno et al. and Ginsberg et al.), which are based on the bandgap difference between the parent phase and the newly formed I-rich phase as driving force predict the phase-distributions in the segregated state qualitatively well. However, a more refined model is necessary to rationalize our experimental results quantitively.
We propose a modified gap-model, based on a two-step segregation process. The first step corresponds to the nucleation of photo-segregation, which is thermodynamically driven by the energy reduction of charge carriers accumulating in I-rich domains.[3,4] This triggers reactions that lead to more persistent changes in the compositional distribution in the mixed halide materials. Our experimental results highlight the importance of understanding the interplay between photo-induced changes in the ionic defect density, which can also be related to other dynamic effects observed in these ionic-semiconductors, such as self-healing and hysteresis.