Electron‐Phonon Interactions Facilitating Large Polaron‐Related Charge‐Carrier Dynamics for Efficient Perovskite Nanocrystal Solar Cells

Recent years have witnessed the accelerated development of optoelectronic devices based on lead halide perovskites-based nanocrystal (NC) films. Yet, to date we have limited knowledge on how the NC's surface affects the long-range charge-carrier dynamics in these films. In this work, we exchange the native ligands on the surface of CsPbI₃ NCs with three different thiopheneammonium-based ligands. Among them, the custom-synthesized 2-thiophenepropenammonium iodide (TPAI) is found to significantly affect the collective phonon states in the NC films, and specifically decrease the strength of the carrier-lattice interactions (by ∼half when compared to the other thiopheneammonium-based ligands). This in turns promoted the formation of large polarons, which are beneficial for charge-carrier dynamics. By employing the TPAI-optimized CsPbI₃ NC films to fabricate solar cells, a champion efficiency of 16.67% is achieved. Additionally, TPAI fostered excellent device stability in ambient air (91.8 ± 0.4% of the initial efficiency after 1100 h) and under light soaking conditions (84.6% after 1000 h). This work provides a rationale connecting the type of surface ligand molecules with the strength of carrier-lattice interactions, thus proving additional insights into mechanisms governing charge-carrier dynamics in NC film-based devices.