Operando Microscopy Characterization of Perovskite Solar Cells

In this work, we developed operando Kelvin probe force microscopy (KPFM) to study the electrostatic potential distribution across perovskite cells under light and forward bias to gain a deeper understanding of device operation physics. As a case study, we selected perovskite cells with a SnO2-based electron-selective layer (ESL), which showed great potential for fabricating high-efficiency, hysteresis-free devices due to the deeper conduction band and higher electron mobility of SnO2. The as-made device showed a main junction at the perovskite/spiro interface. After light soaking and applying forward bias, the junction quality improved, possibly explained by filling trap states at the interfaces and by the perovskite absorber perhaps having a self-poling effect; the main junction is observed at the ESL/perovskite interface. The results are consistent with current-voltage measurements, device performance improves mainly with fill factor enhancement. The operando KPFM results should more closely reflect the real case during current density-voltage measurements or solar cell operation. The operando KPFM technique that we have developed can be a powerful tool to provide a deeper understanding of the device operation mechanism and to further optimize the device.