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.