Bidentate Coordination-Induced Trap Passivation and Phase Stability in Perovskite Solar Cells via Ionic Liquid Engineering

Ionic liquid (IL) engineering has emerged as a promising strategy to improve the performance and stability of perovskite solar cells (PSCs), especially under ambient processing conditions. In this work, we investigate the role of 1-(2-ethoxyethyl)-1-methylpyrrolidinium dicyanamide (Pyr-DCA) as an additive for perovskite precursor solutions and compare its passivation effects with those of the widely used thiocyanate (SCN⁻)-based IL. Density functional theory (DFT) simulations reveal that DCA⁻ exhibits stronger binding affinity to undercoordinated Pb²⁺ ions due to its bidentate nitrogen coordination, effectively passivating deep-level trap states. Incorporation of Pyr-DCA into the perovskite film leads to increased grain size, improved crystallinity, and lower trap density, resulting in enhanced charge carrier lifetimes and reduced nonradiative recombination. Devices treated with Pyr-DCA show improved power conversion efficiency (PCE), moisture resistance, and long-term operational stability. In-situ GIWAXS measurements performed under 1 Sun illumination and electrical bias confirm that DCA⁻ suppresses the formation of degradation-associated δ-phase and PbI₂ , maintaining the structural integrity of the perovskite α-phase. This work highlights the dual chemical and structural stabilization offered by DCA⁻ and demonstrates its promise for enabling scalable and stable PSC fabrication under ambient conditions.