Aromatic nucleophilic substitution polymerization was used to synthesize five poly(ether nitrile imide)s (PENIs) that include benzonitrile and bulky cardo groups from a mixture of phenolphthalein (PP), 4,4′-bis(4-fluorophthalimide) diphenyl ether (4,4′-BFPI), and 2,6-difluorobenzonitrile (DFBN). The structure and properties relationship of PENIs with different ratios of DFBN and 4,4′-BFPI was explored. It was found that the glass transition temperature ( T g ) of PENIs decreased from 280 to 260°C, while the temperature of 5% thermal weight loss ( T 5% ) in N 2 increased from 429 to 453°C as the benzonitrile content in PENI increased. The produced PENI films had good mechanical characteristics, including tensile strengths of 103–112 MPa, elongations at break of 5.6%–8.2%, and tensile moduli of 2.9–3.4 GPa. Furthermore, the solubility and melt processability were also improved with the introduction of the benzonitrile group. Compared with poly(ether ketone imide)s (PEKIs) and poly(ether sulfone imide)s (PESIs), PENIs with benzonitrile displayed higher T g , tensile modules, and lower complex viscosity.
Perovskite solar cells (PSCs) have achieved tremendous success in advancing high power conversion efficiencies. However, defect-induced recombination at grain boundaries (GBs) and the surface of polycrystalline perovskites seriously hinder the further performance enhancement and environmental stability of PSCs. Here, a simple passivating molecule, 4-nitrophthalonitrile (4NPN) with σ–π accepting nitro (–NO2) and cyano groups (–CN), was employed to passivate the charged defects in perovskites. The addition of electron-deficient 4NPN into the perovskite layer of PSCs could not only enhance VOC and the FF, leading to high PCE over 22% but also improved environmental stability. These improvements were attributed to the effective passivation of the defects in the perovskite film by the strongly polarized nitro/cyano groups. In addition, the electron-deficient 4NPN could slightly adjust the energy level of the perovskite facilitating more efficient hole transfer. This work demonstrates the role of strong electron-withdrawing nitro/cyano groups in passivating the vacancy-defects of perovskites and 4NPN as a simple passivator conducive to obtaining high-performance PSCs.
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