Controlling the morphology of organic donor–Acceptor films for enhanced optoelectronic properties

• A comparison of film morphologies created using three coating methods is provided • Convective self-assembly produces structures with solid photoluminescence quenching • Advanced solvent vapor annealing generates larger phase-separated domains The molecular arrangements at the micro- and nanoscale play a decisive role in the performance of organic optoelectronic devices. These arrangements can be effectively controlled through various processing strategies. Here, we propose and systematically compare three different film fabrication and processing approaches—conventional spin-coating, convective self-assembly, and space-confined solvent vapor annealing—to tailor the morphology of donor–acceptor thin films prepared from different material combinations. Results obtained using atomic force microscopy and photoluminescence spectroscopy reveal that the microstructure of fabricated films is critically dependent on the processing technique employed. While spin-coated films exhibit relatively fine and random, ill-developed features, serving as a reference state, convective self-assembly directly produces well-developed morphologies, yielding more favorable conditions for photoluminescence quenching, which is critical for high-performing organic photovoltaics. In contrast, space-confined solvent vapor annealing promotes extensive phase separation and drives the development of larger domains, generating complex supramolecular structures. While such morphologies result in slightly lower photoluminescence quenching efficiencies, they are advantageous for applications such as organic field-effect transistors, where enhanced crystallinity supports efficient charge transport.