Print-compatible morphology optimization strategy reduces the lab-to-module performance gap in organic photovoltaics

Spin-coating technology remains extensively employed in laboratory settings for processing high-efficiency small-area organic photovoltaics. However, when scaling up from cell-level to module-scale fabrication, the spin-coating process-influenced by interfacial wetting behavior and film formation kinetics-produces non-uniform morphological characteristics across both macro- and micro-scales within active-layer films. To address this challenge, we introduce a co-solvent strategy incorporating chloroform (CF), a secondary solvent with lower boiling point and higher surface tension, into chlorobenzene (CB). This formulation optimizes interfacial wetting dynamics, enhances Marangoni velocity, and regulates film formation kinetics. Rheological analysis of the active-layer solution coupled with morphological characterization demonstrates that the co-solvent system enables effective regulation of the film deposition process, which yields uniform large-area films (25 cm²) with optimal phase-separated network structures. The resultant PM6:L8-BO:BTP-eC9 modules processed with co-solvent not only exhibit a notable efficiency of 16.52 % and a fill factor of 74.13 %, which is better than both pure CB- and CF-processed counterparts, but also present the impressive stability. Crucially, slot-die-coated modules fabricated using this co-solvent strategy maintain a competitive PCE exceeding 16 %, underscoring the critical importance of interfacial wetting optimization and kinetic control in developing high-performance, industrially viable photovoltaic modules.