Organic solar cells spray-coated in air with enhanced efficiency and stable morphology

Spray coating is a promising technique for the scalable fabrication of organic solar cells (OSCs) owing to its high compatibility with arbitrarily shaped substrates. However, the insights and analyses from the widely used spin-coating technique cannot be directly transferred to spraying. In this work, we systematically investigate the transformation from conventional spin-coating to spray coating for a representative OSC system, PM6 : DTY6 : L8-BO. The conventionally used chloroform (CF) solvent in spray coating leads to a significant drop in the power conversion efficiency (PCE) and stability, owing to an inferior morphology, while optimized toluene (TL) films enable superior performance and enhanced long-term stability. In situ spectroscopy and systematic morphology investigations reveal that the two solvents exhibit distinct film formation kinetics, with TL promoting a more gradual and uniform assembly process, leading to more favorable molecular packing and reduced amorphous clustering. The optimized TL-sprayed device achieved a PCE comparable to the spin-coated one and maintained 97% of its initial performance after 1000 h of thermal aging at 65 °C. These findings highlight the critical role of morphology modification in performance and stability during processing technique transformation.