Nonbonding Electron Pairs in Cyano and Carbonyl Groups Act as Defect Passivation in Hybrid Perovskite Solar Cells

Stability issues in organic–inorganic perovskite solar cells (PSCs) hinder their commercial use primarily due to defects in the perovskite layer. Addressing these defects, the introduction of passivating agents as additives has significantly advanced the PSC technology. In this work, we synthesized and characterized a donor–acceptor–donor molecule, 4,6-bis(9-ethyl-9H-carbazol-3-yl)-2-oxo-1,2-dihydropyridine-3-carbonitrile (CzCy), designed to address surface defects in perovskite films through passivating Lewis groups. CzCy's strong polarity ensures effective solvation in dimethyl sulfoxide (DMSO) but limited solubility in chlorobenzene (CB). We applied CzCy both as a passivation layer and to dope it into the perovskite to assess its impact on optical and electronic properties and device performance. The Lewis groups in CzCy effectively passivate positive charge defects by coordinating with uncoordinated lead (Pb2+), demonstrating its efficiency in mitigating charged defects within the perovskite layer. When used as a surface passivator in planar devices, CzCy increased the power conversion efficiency (PCE) to 20.51 from 19.48% in devices without it. This improvement is due to the enhanced nonbonding interaction between CzCy and the perovskite surface, boosting photovoltaic performance and extending material lifespan.