In-depth Characterization Methodology for the Assessment of Passivation Impact in Halide Perovskite Solar Cells

Abstract

Passivation is playing a significant role in achieving excellent performance in perovskite solar cells. However, traditional characterization in this context is often limited to the analysis of current-voltage (IV) and sometimes the analysis of superficial chemical properties via UV or X-ray photoelectron spectroscopy (UPS or XPS). This is not sufficient in order to provide a full understanding of the passivation impact and target the best passivation strategies. In this work, a more developed characterization protocol is introduced, aiming at establishing a clearer link between nano-scale electrical properties and macro-scale device characteristics. Traditional IV measurements are combined with admittance spectroscopy (AS) and deep-level transient spectroscopy (DLTS) for the analysis of charge-related performance losses and with Time-of-Flight Secondary Ion Mass Spectrometry (ToF SIMS) to complete the understanding of ionic accumulation at the perovskite interfaces. This protocol is tested on two experimental devices, a reference MAPI-based p-in perovskite cell and the same cell passivated at both perovskite interfaces. First, IV measurements show an increase of both Voc and FF of approximately 10% for the passivated cell, with an absolute efficiency increase of 4%. AS measurements suggest that the higher FF in the passivated sample cannot be attributed to a lower series resistance, but possibly to a lower diffusivity of some ionic species present at the interface. Analysis of the DLTS response yields an activation energy of 0.37 eV. The pre-exponential factor for these ions is lower for the passivated cell, which is also suggested by the higher Voc. Finally, preliminary ToF SIMS results showcase different ionic species that accumulate at the perovskite interfaces. Overall, this novel characterization approach enables a rather comprehensive understanding of the device and points to leads for future work about passivation for perovskite solar cells.