Solvent and Bar Coating Parameter Selection for Optimum Deposition of Perovskite Films at Low Temperatures under Ambient Conditions

The transition from small-area and atmosphere-controlled spin-coating to large-area bar coating in an uncontrolled ambient process requires a comprehensive understanding of the crystallization kinetics in perovskite precursor layers. In this work, we investigate the structural, optical, and photovoltaic properties of additive-free methylammonium lead triiodide (MAPbI3) films fabricated via bar coating without a glove box. We analyze these properties as a function of the precursor solvent system, plate temperature, and bar groove depth. The solvent strategy employs a mixture of 2-methoxyethanol (2ME), acetonitrile (ACN), and N-methyl-2-pyrrolidone (NMP) to regulate nucleation and growth at low processing temperatures (24–50 °C). Our findings indicate that the volumetric ratios of the solvent components and the plate temperature are critical in determining crystallinity, optical homogeneity, and film compactness. In contrast, the bar groove depth primarily modulates film morphology and compactness, with a less pronounced effect on the material’s intrinsic structural or optical properties. By optimizing the synergy between solvent chemistry and physical coating parameters, the power conversion efficiencies (PCE) were enhanced from 7 to 11.85% under relative humidity >35%. This study establishes a processing protocol that may facilitate future scale-up of bar-coated perovskite films.