Mapping of Internal Ionic/Electronic Transient Dynamics in Current-Voltage Operation of Perovskite Solar Cells

Metal halide perovskites are mixed ionic-electronic semiconductors that involve an important and particular phenomenology that negatively affects the performance and stability of next-generation photovoltaic devices based on such material. The ionic nature of perovskites is shown to undergo not only a simple redistribution of charges but also influences the electronic processes and ultimately the steady-state device operation. Nevertheless, a comprehensive understanding of the internal contributions of ionic and electronic conductivities to the evolution of current during device performance experiments and to degradation losses in ageing tests is currently missing. Here the ionic- and electronic-based currents are separately shown in photovoltaic perovskites by means of transient experiments, beyond the external measured response. From an advanced mathematical model, the experimental observations attributing the partial transient features to physical effects in perovskites are rationalized. It is revealed that ion-driven surface recombination effects are a dominant factor in the slowdown of efficiency measurements and in the long-term degradation of perovskites under operational conditions. This work contributes to tracing a more accurate physical picture of the complex energy landscape of the perovskite-based solar cells, which will be key to taking steps toward industrialization.