Solvent-Activated Transformation\nof Polymer Configurations\nfor Advancing the Interfacial Reliability of Perovskite Photovoltaics

Organic materials have been widely used as the charge\ntransport\nlayers in perovskite solar cells due to their structural versatility\nand solution processability. However, their low surface energy usually\ncauses unsatisfactory thin-film wettability in contact with the perovskite\nsolution, which limits the interfacial performance of the photovoltaic\ndevices. Although solvent post-treatment could occasionally regulate\nthe wetting behavior of organic films, the mechanism of the solid–liquid\ninteraction is still unclear. Here, we present evidence of a possible\ncorrelation between the solvent and the wettability of a conventional\npolymer, poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA),\nand reveal the critical roles of Hansen solubility parameters (HSPs)\nof solvents in wetting mechanisms. Our results suggest that the conventional\nsolvent <i>N</i>,<i>N</i>-dimethylformamide (DMF)\nimproves the wettability of PTAA by the morphological disruption mechanism\nbut negatively impacts interfacial charge collection and stability.\nIn contrast, 2-methoxyethanol (2-Me) with an appropriate HSP value\ninduces the transformation of the PTAA configuration in an orderly\nmanner, which simultaneously improves the wetting property and maintains\nthe film topography. After careful optimization of the surface conformation\nof the PTAA film, both perovskite crystallization and interfacial\ncompatibility have been enhanced. Benefiting from superior interfacial\nproperties, the perovskite solar cells based on 2-Me deliver a champion\nefficiency of 24.15% compared to 21.4% for DMF-based ones. More encouragingly,\nthe use of 2-Me minimizes the perovskite buried interfacial defects,\nenabling the unencapsulated devices to maintain about 95% of their\ninitial efficiencies after light illumination for 1100 h. The present\nstudy demonstrates the high effectiveness of solvent–polymer\ninteraction for adjusting interfacial properties and strengthening\nthe robustness of perovskite solar cells.