How temperature impacts material properties and photovoltaic performance of mixed-halide perovskite via light-induced ion migration

Lead halide perovskites applied in solar cells have gained significant attention due to their rapidly increasing power conversion efficiency. However, their intrinsic instability, stemming from their ionic nature, hampers the commercialization of perovskite solar cells. The scope of this paper is to extend the characterization of light-induced ion migration via temperature-dependent measurement based on the polaron-invoked ion migration model. The investigation reveals that light-induced phase segregation intensifies with rising temperature, as indicated by stoichiometry variation and crystal compression. This intensification facilitates the formation of iodide-rich domains within the perovskite film. The formation of such domains is correlated with promoted carrier recombination in perovskite solar cells, as observed through electrochemical impedance spectra. Consequently, the facilitated carrier recombination process leads to a notable decline in the power conversion efficiency of a perovskite solar cell, reducing to <20% of its original value as the temperature increases from 300 K to 500 K. Moreover, the intensified ion migration due to heat also impacts the stability of both the perovskite material and the whole device. Extended illumination duration and high temperature lead to the decomposition of perovskite, resulting in the formation of insulated PbI₂ that deteriorates the performance of perovskite solar cells. This degradation is irreversible and results in rapid decomposition at high temperatures, as evidenced by the deterioration of photovoltaic performance of perovskite solar cells within 30 minutes of operation at 500 K. The temperature-dependent characterization reveals a cascading process originating from light-induced ion migration, followed by phase segregation and iodide-rich domain formation. These processes significantly impact the perovskite solar cells in terms of carrier transport/recombination behavior and operational stability.