Multifunctional Conjugated Polyphenol “Bridge” Capped the Upper Interface of Highly Efficient and Stable Inorganic Perovskite Solar Cells Fabricated in Air

Carbon-based all-inorganic perovskite solar cells (C-PSCs) are promising alternatives compared with conventional organic–inorganic halide PSCs because of their good thermal stability. However, low carrier transport efficiency and energy level mismatch of the upper interface of the device limit the further improvement of power conversion efficiency (PCE), and all-inorganic perovskites are extremely sensitive to oxygen and humidity, which seriously damages the long-term stability of the device. Upper interface modification is an effective solution to improve the PCE and the stability of devices. Unfortunately, many traditional interface modifiers exhibit insulated and hygroscopic characteristics, which may be harmful to the performance of the device. Herein, a multifunctional conjugated polyphenol “bridge” strategy was adopted on the upper interface of the device fabricated in air, that is, stilbene and polyhydroxy stilbene were capped on perovskite. The results demonstrate that they can effectively enhance the energy level alignment, improve charge transport, passivate defects, suppress nonradiative recombination of interface, and resist oxygen and moisture in air, and the positive effects of modification become more and more pronounced with the increment of the number of hydroxyl groups. The PCE of PSCs was improved from 11.10 to 13.10% after modification. In addition, the unencapsulated modified devices exhibited better stability than the control devices under different environmental conditions.