Defect Signatures in Admittance Spectroscopy of Perovskite Solar Cells

Understanding defect properties is key to improving the performance of solar cells. Thermal admittance spectroscopy (TAS) is widely used to analyze the properties of defect states in semiconductor devices. However, evaluating the defect capacitance signatures in admittance spectra is still problematic in emerging solar cells and needs to be clarified. The behavior of charge trapping and detrapping that introduces the capacitance step depends on the correlation between the defect properties with the applied temperature and frequency. Therefore, to understand the capacitance signatures of defects in the admittance spectra of perovskite solar cells, we perform detailed simulations using the one-dimensional (1D) solar cell capacitance simulator (SCAPS) software. The capacitance step can be introduced depending on the interplay between the defects and the measurement conditions. We found that the capacitance step at low frequencies is dominated by deep defects with large capture cross-sections, while the capacitance step of defects at high frequencies is dominated by shallow defects with small capture cross-sections. This indicates that not all deep or shallow defects are measurable by admittance spectroscopy due to the system's capability.