Multifunctional Thiophene Cascading SnO 2 /Perovskite Interfaces for Efficient and Stable MAPbI 3 Photovoltaics.

The power conversion efficiency (PCE) and stability of n-i-p perovskite solar cells (PSCs) are significantly affected by inherent defects of SnO 2 and perovskite layers. In this work, we incorporate 2-bromo-3-thiophenic acid (BrThCOOH) as a multifunctional passivant to simultaneously passivate the defects of SnO 2 surface and perovskite layer. BrThCOOH permeates evenly into the MAPbI 3 and coordinates with Pb 2+ and iodine vacancies (V I + ) to reduce surface defect density and inhibit the decomposition of MAPbI 3 . Carboxylic acid effectively passives the oxygen vacancy on the surface of SnO 2 through coordination bonds, reducing the probability of electron capture by SnO 2 surface defects, thus contributing to electron transport in device. The interaction of BrThCOOH with MAPbI 3 and SnO 2 surfaces leads to an upward shift in energy levels, reducing energy loss during charge migration. The optimal MAPbI 3 device with BrThCOOH-modified SnO 2 (T-SnO 2 ) reveals an improved PCE of 21.12%, much higher than that of the control one (19.12%). The hydrophobicity of BrThCOOH-modified MAPbI 3 is also improved, which is beneficial to the durability of the device. After 100 h of storage in the environment, the generated PSCs maintain their initial PCE of 75%, demonstrating excellent long-term stability without any encapsulation.