Nonbonding Electron\nPairs in Cyano and Carbonyl Groups\nAct as Defect Passivation in Hybrid Perovskite Solar Cells

Stability issues in organic–inorganic perovskite\nsolar cells\n(PSCs) hinder their commercial use primarily due to defects in the\nperovskite layer. Addressing these defects, the introduction of passivating\nagents as additives has significantly advanced the PSC technology.\nIn this work, we synthesized and characterized a donor–acceptor–donor\nmolecule, 4,6-<i>bis</i>(9-ethyl-9<i>H</i>-carbazol-3-yl)-2-oxo-1,2-dihydropyridine-3-carbonitrile\n(<b>CzCy</b>), designed to address surface defects in perovskite\nfilms through passivating Lewis groups. <b>CzCy</b>’s\nstrong polarity ensures effective solvation in dimethyl sulfoxide\n(DMSO) but limited solubility in chlorobenzene (CB). We applied <b>CzCy</b> both as a passivation layer and to dope it into the perovskite\nto assess its impact on optical and electronic properties and device\nperformance. The Lewis groups in <b>CzCy</b> effectively passivate\npositive charge defects by coordinating with uncoordinated lead (Pb<sup>2+</sup>), demonstrating its efficiency in mitigating charged defects\nwithin the perovskite layer. When used as a surface passivator in\nplanar devices, <b>CzCy</b> increased the power conversion efficiency\n(PCE) to 20.51 from 19.48% in devices without it. This improvement\nis due to the enhanced nonbonding interaction between <b>CzCy</b> and the perovskite surface, boosting photovoltaic performance and\nextending material lifespan.