A High Mobility Conjugated Polymer Enables Air and Thermally Stable CsPbI₂Br Perovskite Solar Cells with an Efficiency Exceeding 15%

Abstract Inorganic cesium lead halide perovskite solar cells (PSCs), such as CsPbI₂Br, have made a striking breakthrough with a power conversion efficiency of over 16%. However, CsPbI₂Br is known to be very sensitive to moisture, and the intrinsic long‐term stability of CsPbI₂Br film remains a critical challenge. Interface engineering has been proven to be an effective way for solving the instability‐to‐moisture issue and enhancing the performance of inorganic–organic hybrid PSCs, while there are a few reports on interface engineering for inorganic PSCs. Here, a conjugated polymer, poly(N‐alkyldiketopyrrolo‐pyrrole dithienylthieno[3,2‐b]thio‐phene) (DPP‐DTT), with high mobility is introduced as a novel interface passivation for CsPbI₂Br PSCs, which can significantly reduce nonradiative recombination in perovskite, leading to significant enhancement in both efficiency and stability of CsPbI₂Br PSCs. Through DPP‐DTT passivation, a champion efficiency of 15.14% is obtained in CsPbI₂Br PSCs. Moreover, the Lewis base DPP‐DTT can serve as an ultrahydrophobic agent to hold the photovoltaic performance of CsPbI₂Br PSCs under ambient environment with humidity or thermal stress. These results provide a simple while highly effective route of fabricating the highly efficient and stable inorganic PSCs.