Enhancing Flexibility, Long-Term Stability, and Efficiency in Full Air Fabricated Perovskite Solar Cells via Multifunctional Fluorinated Polyurethane Additives

Perovskite films often suffer from surface and grain boundary defects, including uncoordinated ions, lattice distortions, and dangling bonds, coupled with lattice distortions due to solvent volatilization anisotropy and the thermal expansion coefficient. Such defects severely compromise both the photovoltaic efficiency and long-term solar cell stability. Here, fluorinated polyurethane (FPU) was synthesized and introduced into the perovskite precursor as a multifunctional additive. Excess Pb²⁺ ions interact with the carbonyl group (C═O) of FPU, thereby reducing nonradiative recombination. The perovskite and FPU form various hydrogen bonds via MA⁺ with F and -NH with -I. This multiplies the passivation of grain boundary defects, increases grain size, reduces defect density, releases residual lattice stress, and facilitates charge transport. Accordingly, the power conversion efficiency of the FPU-modified perovskite solar cells (PSCs) on rigid substrates and flexible substrates reached 21.18 and 17.76%, respectively. Notably, the long-chain C-F compound, which constructs a moisture-resistant barrier, could inhibit moisture corrosion in the perovskite films. After 2000 h of storage at ambient temperature in dark, the PSCs's initial efficiency still remained 82%. Additionally, after it undergoes 300 bending cycles (<i>r</i> = 0.7 cm), the device maintains 92.4% of its initial efficiency.