Detrimental Defect Cooperativity at TiO<sub>2</sub>/CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Interface: Decreased Stability, Enhanced Ion Diffusion, and Reduced Charge Lifetime and Transport
Kaiping Wang, Zhiwei Wu, Kai-Feng Wang, Hao-Ting Xu, Jun He, Bo Wen, Chuan‐Jia Tong, Limin Liu, Oleg V. Prezhdo
Abstract
Interfaces are essential for solar cell performance since they govern charge separation and transport. Using quantum dynamics simulation, we demonstrate that at interfaces, common defects that are benign on their own, iodine vacancy in CH 3 NH 3 PbI 3 (V I ) and oxygen vacancy in TiO 2 (V O ), are responsible synergistically for poor stability and charge losses. V O promotes V I diffusion and accelerates iodine migration. A midgap trap state appears, inhibiting charge transport and accelerating charge recombination by an order of magnitude. Strong structural distortions strengthen electron-vibrational interactions and activate high-frequency TiO 2 phonons. Because of the widely reported high defect-tolerance of lead-halide perovskites, the synergistic detrimental influence of perovskite defects with defects in other materials is often overlooked. The interfacial defect pairing could be a major reason for poor stability and charge losses in perovskite solar cells. The results suggest that either a high-quality perovskite or high-quality charge extraction layer may be sufficient to achieve high performance.