A green solvent enables precursor phase engineering of stable formamidinium lead triiodide perovskite solar cells

Nonvolatile and Strongly Coordinating Solvent Enables Blade-coating of Efficient FACs-based Perovskite Solar Cells

Blade-coating has emerges as a critical route for scalable manufacturing of perovskite solar cells. However, the N2 knife-assisted blade-coating process under ambient conditions typically yields inferior-quality perovskite films due to inadequate nucleation control and disorderly rapid crystallization. To address this challenge, a novel solvent engineering strategy is developed through the substitution of N-methyl-2-pyrrolidone (NMP) with 1,3-dimethyl-1,3-diazinan-2-one (DMPU). The unique physicochemical properties of DMPU, characterized by low vapor pressure, strong coordination capability, and limited PbI2 solubility, synergistically regulate nucleation and crystallization kinetics. This enables rapid nucleation, stabilization of intermediate phases in wet films, and controlled crystal growth, ultimately producing phase-pure perovskite films with reduced defect density. Moreover, the feasibility and superiority of the mixed solvent strategy are demonstrated. The optimized blade-coated PSCs achieve a power conversion efficiency of 21.74% with enhanced operational stability, retaining 84% initial efficiency under continuous 1-sun illumination for 1,000 h. This work provides new insights into solvent design for preparing blade-coated perovskite films.

Suppressing Polaronic Defect-Photocarrier Interaction in Halide Perovskites by Pre-distorting Its Lattice

In halide perovskites, photocarriers can have strong polaronic interactions with point defects. For iodide-deficient MAPbI3, we found that the Fermi level can shift significantly by 0.6-0.7 eV upon light illumination. This energy level shift is accompanied by the formation of deep electron traps. These experimental observations are consistent with the formation of a Pb-Pb dimer when photoexcited electrons are trapped at an iodide vacancy. Interestingly, we found that this polaronic interaction is suppressed when a portion of MA+ cations is replaced by smaller Cs+ ions. Density functional theory calculations reveal that Cs-doping can reduce the distance between two Pb atoms across an iodide vacancy, even without electron trapping. The predistortion of the lattice induced by cation replacement resembles the Pb-Pb dimer formed by electron trapping at the defect site, which explains the suppression of light-induced effects observed in the experiment. Our finding unveils a counterintuitive strategy to enhance the photostability of halide perovskites by preintroducing distortions into its lattice.