Electronic Coordination Effect of the Regulator on Perovskite Crystal Growth and Its High-Performance Solar Cells

The rapid growth of perovskite crystals leads to excessive grain boundaries and surface defects, which have a negative effect on the performance of solar cells (PSCs). Passivating defects by controlling the crystal growth rate becomes a crucial research hotspot for preparing high-crystallinity perovskite films. In this work, phenylacetonitrile (PA) and 2-naphthylacetonitrile (2-NA) serving as crystal growth regulators are introduced into the perovskite precursor. The coordination effect of lone-pair electrons (n-electrons) and π-electrons in the regulator molecule with Pb²⁺ on the nucleation and growth of FA_0.80MA_0.15Cs_0.05Pb(I_0.85Br_0.15)₃ perovskite crystal along with the passivation of surface defects and grain boundaries are systematically investigated. The n-electrons of N atom form a coordination bond with Pb²⁺, and the π-electrons in the aromatic ring generate a cation-π interaction with Pb²⁺. This combined effect efficiently delays the crystallization rate of the perovskite crystal and then promotes the grain growth and reduces the grain boundaries, which is favorable for the dissociation of more excitons to carriers. The PA-optimized PSCs shows an increase of power conversion efficiency (PCE) from 18.01 to 21.09%, with an unencapsulated device retaining 91.2% of its initial efficiency for 60 days in 40 ± 5% relative humidity under dark conditions.