Two-Dimensional Conjugated Polymeric Nanocrystals for Organic Electronics

Two-dimensional (2D) materials have attracted greatest attention in the past years. In this study, we report 2D conjugated polymeric nanocrystals, polyhedral oligomeric silsesquioxanes (POSS) covalently bonded with main chain of poly(3-hexylthiophene) (P3HT) without utilization of a template or an exfoliation protocol. The 2D crystal structure of POSS-P3HT are systematically investigated and confirmed by wide-angle X-ray diffraction, transmission electron microscopy, scanning electron microscopy, atomic force microscopy and computational simulation. It is found that the resultant crystals possess long-range-order parallel to the 2D plane of the packed POSS units, where the P3HT moieties are “sandwiched” between two POSS layers, forming 2D nanocrystals. As a result, the P3HT moieties retain its orientation ordered crystal structure, resulting in enhanced charge-carrier mobility, which is verified by the two-terminal diodes based on the space-charged-limited-current method and three-terminal field-effect transistors. Further studies indicate that organic photovoltaics by 2D POSS-P3HT nanocrystals blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) possess over 40% enhancement in power conversation efficiency compared to that by the one-dimensional (1D) P3HT blended with PC61BM. Our studies provide a new and practical platform for directing growth of 2D conjugated polymeric nanocrystals for boosting device performance of organic electronics.