Amorphous Poly(3-hexylthiophene) (P3HT) Thin Films by Vacuum Electrospray Deposition

Vacuum electrospray deposition is a promising technique to deposit solvent-free films of polymers or (macro)­molecules that can otherwise be processed only in solution, owing to their thermal fragility. However, the different environments of vacuum and solvent during film growth can have severe effects on the resulting thin-film morphology and structure. Here, we investigate the thin-film growth of the generally semicrystalline conjugated polymer poly­(3-hexylthiophene-2,5-diyl) (P3HT) by vacuum electrospray deposition and juxtapose it with films conventionally grown from solution. We find that, in contrast to the solution-processed films, those from electrospray deposition appear to be entirely amorphous, which we deduce from amorphous scattering in synchrotron grazing-incidence X-ray diffraction, where their diffraction signature resembles that of dropcast films in situ heated close to their melting point. While numerous experimental approaches exist to increase structural order in thin films, deliberately establishing amorphous films is a challenge for semicrystalline materials. Based on our present example of P3HT, vacuum electrospray deposition, therefore, emerges as a thin-film preparation technique that is very well-suited to readily suppress crystallization, which can be of high value for disentangling experimental data obtained for semicrystalline materials.