Solvent-soaking treatment induced morphology evolution in P3HT/PCBM composite films

Morphology of the active layer has been proven to play an important role in determining the final device performance of photovoltaic devices. Herein, we present a facile mixed solvents soaking approach to tailor the morphology of the active layer, in which not only the crystallinity of poly(3-hexylthiophene) (P3HT) in its composite film with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) has been substantially improved, but also an interpenetrating network composed of highly crystalline P3HT and PCBM nanoaggregates is constructed as confirmed by transmission electron microscopy. Furthermore, X-ray photoelectron spectroscopy analysis reveals that P3HT chains enrich at the active layer/anode interface while more PCBM are found to present on the active layer/cathode interface along the vertical direction of the composite films, which is beneficial for charge carrier transport and will contribute to better device performance. The power conversion efficiency of the device using this method is improved to 3.23%, in contrast to 1.45% for a pristine device and 2.79% for a thermally annealed device. Therefore, this simple technique can simultaneously optimize lateral and vertical nanoscale phase separation of crystalline P3HT and PCBM, and shows high potential application in the preparation of high performance cost-effective polymer solar cells.