Efficient and Stable Perovskite Solar Cells with a Multifunctional Spiro‐Based Hole Transport Material

Abstract The widely used spiro‐OMeTAD exhibits moderate interaction with the perovskite layer, which does not decrease the defect on the perovskite surface, thus limiting the photoelectric performance of perovskite solar cells. In this work, the spiro‐OMeTAD structure is functionalized with chlorine (Cl), resulting in a new material labeled spiro‐mCl, which interacts more effectively with the perovskite and passivating interface defects. In addition, the strong electronegativity of Cl lowers the Highest Occupied Molecular Orbitals (HOMO) energy level of spiro‐mCl, resulting in a better match with the valence band of perovskite. Additionally, the asymmetry introduced by Cl enhances the hole mobility and increases the glass transition temperature of spiro‐mCl. As a result, the device incorporating spiro‐mCl achieved an open‐circuit voltage of 1.16 V and a remarkable power conversion efficiency of 25.26% (certified at 24.88%), marking it as one of the highest‐performing spirobifluorene‐based HTMs in PSCs. Importantly, this device also demonstrated significantly improved operational stability compared to the one utilizing spiro‐OMeTAD.