Naphthalene diimide (NDI)-based copolymers are promising polymer acceptors in all-polymer solar cells (all-PSCs), but their large crystal domains cause large-scale phase separation in all-polymer blend films. This limits the photovoltaic performance and mechanical stability of all-PSCs. Herein, we control all-polymer blend films by introducing a fluorinated copolymer of NDI and (E)-1,2-bis(3fluorothiophen-2-yl)ethene (FTVT) (PNDI−FTVT) as a polymer acceptor for flexible all-PSCs. The copolymer PNDI−FTVT has a less crystalline structure and higher electron mobility than its nonfluorinated copolymer counterpart (PNDI− TVT). A blended film incorporating PNDI−FTVT exhibits a well-mixed morphology and improves the chain interconnectivity with a polymer donor, providing better charge transport pathways and enhanced mechanical resilience. The PNDI−FTVTbased flexible all-PSC exhibits enhanced photovoltaic performance in comparison with a PNDI−TVT-based flexible all-PSC (5.11−7.14%) as well as excellent mechanical stability in a flexible all-PSC (7.14−5.78%), maintaining 81% of its initial performance at a bending radius of 8.0 mm after 1000 bending cycles.

The reduction of charge carrier recombination and intrinsic defect density in organic-inorganic halide perovskite absorber materials is a prerequisite to achieving high-performance perovskite solar cells with good efficiency and stability. Here, we fabricated inverted planar perovskite solar cells by incorporation of a small amount of excess organic/inorganic halide (methylammonium iodide (CHNHI; MAI), formamidinium iodide (CH(NH)I; FAI), and cesium iodide (CsI)) in CHNHPbI perovskite film. Larger crystalline grains and enhanced crystallinity in CHNHPbI perovskite films with excess organic/inorganic halide reduce the charge carrier recombination and defect density, leading to enhanced device efficiency (MAI+: 14.49 ± 0.30%, FAI+: 16.22 ± 0.38% and CsI+: 17.52 ± 0.56%) compared to the efficiency of a control MAPbI device (MAI: 12.63 ± 0.64%) and device stability. Especially, the incorporation of a small amount of excess CsI in MAPbI perovskite film leads to a highly reproducible fill factor of over 83%, increased open-circuit voltage (from 0.946 to 1.042 V), and short-circuit current density (from 18.43 to 20.89 mA/cm).

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