CsHFDF bifunctional polar molecule-assisted synergistic passivation for highly efficient and stable perovskite solar cells

Even though lead halide perovskites have achieved impressive photovoltaic performance for their unique properties, inherent deep-level defects and crystal defects still show pivotal impact on efficiency and stability of solar devices. In this research, 1,1,2,2,3,3-Hexafluoropropane-1,3-disulfonimide caesium salt (CsHFDF) is incorporated into the perovskite precursor to synergistically passivate defects and enhance the quality of crystallization. It is found that CsHFDF inhibits the crystallization of lead iodide, which in turn modulates the crystal orientation and growth of the perovskite film. The HFDF¯ anchored at grain boundaries exhibits bifunctional characteristics, effectively reducing undercoordinated FA⁺ and Pb²⁺ defects, meanwhile the incorporated Cs⁺ can enhance the crystal stability. The transient absorption (TA) and time-resolved photoluminescence spectroscopy are utilized to systematically investigate the photophysical processes at the molecular level. The addition of CsHFDF enhanced both carrier bulk diffusion within the perovskite and interfacial transfer at the perovskite/SnO₂ interface, while simultaneously reducing charge recombination from SnO₂ to perovskite. These effects are closely related to the synergistic regulation of perovskite crystal quantity and deep-level defects after CsHFDF doping. Ultimately, perovskite solar cells based on this polar molecule doping achieved a power conversion efficiency of 24.52 % for small-area devices and 21.02 % for large-area (5 cm × 5 cm) perovskite solar modules.