Surface Regulation through Dipolar Molecule Boosting the Efficiency of Mixed 2D/3D Perovskite Solar Cell to 24%

Abstract Mixed 2D/3D perovskite solar cells (PSCs) show promising performances in efficiency and long‐term stability. The functional groups terminated on a large organic molecule used to construct 2D capping layer play a key role in the chemical interaction mechanism and thus influence the device performance. In this study, 4‐(trifluoromethyl) benzamidine hydrochloride (TFPhFACl) is adopted to construct 2D capping layer atop 3D perovskite. It is found that there are two mechanisms synergistically contributing to the increase of efficiency: 1) The TFPhFA + cations form a dipole layer promoting the interfacial charge transport. 2) The suppressed nonradiative recombination of perovskite through the coordination of TFPhFA + cations with Pb–I octahedron, as well as the recrystallization of 3D perovskite induced by Cl ‐ ions. As a result, the PSC delivers an efficiency of 24.0% with improved open‐circuit voltage ( V OC ) of 1.16 V, short‐circuit current density ( J SC ) of 25.42 mA cm ‐2 , and fill factor of 81.26%. The device shows no decrease in efficiency after 1500 h stored in the air indicating the good stability. The utilization of TFPhFACl not only provides a facile way to optimize the interfacial problems, but also gives a new perspective for rational design of large spacer molecule for constructing efficient 2D/3D PSCs.