Stress and Defect Effects on Electron Transport Properties at SnO 2 /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 SnO 2 /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 SnO 2 /perovskite interfaces with various stresses and defects. The results prove that the PbI 2 /SnO 2 interfaces have better structural stability and superior characteristics for the electron transport. The tensile stress could move the conduction band minimum (CBM) of CH 3 NH 3 PbI 3 upward, while the compressive stress could move the CBM of SnO 2 downward. By taking into account the stress effect, the CBM offset is 0.07 eV at the PbI 2 /SnO 2 interface and 0.28 eV at the MAI/SnO 2 interface. Moreover, our calculations classify V I and I i at the PbI 2 /SnO 2 interface and Sn-I, I i and Sn i at the MAI/SnO 2 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.