Dynamic Phenomena at Perovskite/Electron-Selective Contact Interface as Interpreted from Photovoltage Decays

Drastic changes in open-circuit voltage decay (OCVD) response time in CH3NH3PbX3 perovskites have been systematically investigated in order to elucidate the dynamic properties of the interface. Under pre-illumination treatment, the decay times are reduced by orders of magnitude, but if left to rest for sufficient time, the solar cell evolves to its original decay kinetics. In order to explain these observations, we developed advanced modeling of the perovskite solar cell to obtain a realistic description of the immediate vicinity of the interface, including ionic variable concentration and accumulation of holes via degenerate statistics in the space charge region. The results reveal a large amount of majority carriers at the minority carrier extraction contact, assisted by additional ionic charge. The surface band bending related to accumulation gives an electrostatic contribution to the photovoltage in a manner governed by slow dynamics of cations at the electron-selective contact. The modeling of the interface allows us to describe the dynamics of the contact region dominated by surface charging and recombination. These phenomena also play an important role in operation conditions and current-voltage scans of the solar cell.