Analysis of the Influence of Selective Contact Heterojunctions on the Performance of Perovskite Solar Cells

Knowledge of the mechanisms that take place at the selective contacts, located at the charge-transport-layer (CTL)/perovskite heterojunctions, is crucial for the optimization of perovskite solar cells. Anomalous high values of the low-frequency capacitance at open-circuit and short-circuit indicate a high accumulation of charge at the interfaces, which could hinder the extraction of charge and increase hysteresis in current–voltage curve. To investigate this issue, we develop a simulation model based on the drift-diffusion differential equations with specific boundary conditions at the interfaces. We have simulated the CTL/perovskite structures as part of the entire perovskite solar cell, in order to establish the realistic energy profile across the interfaces. The energy profile allows to detect in which situations free charge accumulation at the interfaces exists, and to quantify this accumulation as a function of the device and material parameters. We discuss the role and the importance of each CTL/perovskite interface at open-circuit and short-circuit. We conclude that the accumulation of charge at the interfaces is strongly affected by the specific contact materials, and critically depends on a compromise between the presence of ions, the values of the carrier mobility, and the interfacial and bulk recombination parameters.