Enhancing Flexibility,\nLong-Term Stability, and Efficiency\nin Full Air Fabricated Perovskite Solar Cells via Multifunctional\nFluorinated Polyurethane Additives

Perovskite films often suffer from surface\nand grain boundary defects,\nincluding uncoordinated ions, lattice distortions, and dangling bonds,\ncoupled with lattice distortions due to solvent volatilization anisotropy\nand the thermal expansion coefficient. Such defects severely compromise\nboth the photovoltaic efficiency and long-term solar cell stability.\nHere, fluorinated polyurethane (FPU) was synthesized and introduced\ninto the perovskite precursor as a multifunctional additive. Excess\nPb<sup>2+</sup> ions interact with the carbonyl group (CO)\nof FPU, thereby reducing nonradiative recombination. The perovskite\nand FPU form various hydrogen bonds via MA<sup>+</sup> with F and\n−NH with −I. This multiplies the passivation of grain\nboundary defects, increases grain size, reduces defect density, releases\nresidual lattice stress, and facilitates charge transport. Accordingly,\nthe power conversion efficiency of the FPU-modified perovskite solar\ncells (PSCs) on rigid substrates and flexible substrates reached 21.18\nand 17.76%, respectively. Notably, the long-chain C–F compound,\nwhich constructs a moisture-resistant barrier, could inhibit moisture\ncorrosion in the perovskite films. After 2000 h of storage at ambient\ntemperature in dark, the PSCs’s initial efficiency still remained\n82%. Additionally, after it undergoes 300 bending cycles (<i>r</i> = 0.7 cm), the device maintains 92.4% of its initial efficiency.