Stress and Defect Effects on Electron Transport Properties at SnO2/Perovskite Interfaces: A First-Principles Insight

The structural and electronic properties of interfaces play an important role in the stability and functionality of solar cell devices. Experiments indicate that the SnO2/perovskite interfaces always show superior electron transport efficiency and high structural stability even though there exists a larger lattice mismatch. Aiming at solving the puzzles, we have performed density-functional theory calculations to investigate the electronic characteristics of the SnO2/perovskite interfaces with various stresses and defects. The results prove that the PbI2/SnO2 interfaces have better structural stability and superior characteristics for the electron transport. The tensile stress could move the conduction band minimum (CBM) of CH3NH3PbI3 upward, while the compressive stress could move the CBM of SnO2 downward. By taking into account the stress effect, the CBM offset is 0.07 eV at the PbI2/SnO2 interface and 0.28 eV at the MAI/SnO2 interface. Moreover, our calculations classify V-I and I-i at the PbI2/SnO2 interface and Sn-I, I-i and Sn-i at the MAI/SnO2 interface as harmful defects. The I-i defects are the most easily formed harmful defects and should be avoided at both interfaces. The calculated results are in agreement with the available experimental observations. The present work provides a theoretical basis for improving the stability and photovoltaic performance of the perovskite solar cells.