Cooperative Assembly Of Pyrene-functionalized Diblock Copolymers And Its Application In Polymer Solar Cells

In recent years, organic solar cells have received widespread attention for thecharacteristic of lightweight, strong flexible and low cost. However, the photoelectricconversation of the organic solar cells is relatively low, and the stability is not sogood, which restrict its application and development in the commercial. In order toimprove the photoelectric conversion efficiency and stability of organic solar cells,the work has been carried out in two aspects. On the one hand, we have designed andsynthesized new donor and receptor materials to regulate the morphology of theactive layer. On the other hand, the photovoltaic device performace has been furtheroptimized by using high conductivity of composite materials as the interface layer.The works are divided as follows:Firstly, a facile approach to develop the stable and well-defined bulkheterojunction (BHJ) nanomorphology has been demonstrated. Novel pyrene (Py)-functionalized diblock copolymers poly(3-hexylthiophene)-block-poly[3-(10-(pyren-1-yloxy)decyloxy)thiophene](P3HT-b-P3TPy), and pyrene-functionalized fullerene[6,6]-phenyl-C61-butyric acid1-pyrene butyl ester (PCBPy), were successfullysynthesized. The π-π interactions of Py mesogens interdigitated between thefunctionalized fullerene and P3TPy segment can allow for the cooperative assemblyof P3HT-b-P3TPy and PCBPy. The orientation of the Py mesogens also can furtherenhance the molecular arrangement. Compared with the as-cast and thermalannealing, solvent annealing can promote cooperative assembly of P3HT-b-P3TPy:PCBPy undergoing the slow film growth. Note that the assembly microstructurestrongly depends on the molar ratio of P3HT and P3TPy with Py mesogens. Lowloading of P3TPy block in the copolymers blends keeps the same behavior to theP3HT, while relatively high loading of Py mesogens favors the better intermolecularπ-π stacking interactions between P3HT-b-P3TPy and PCBPy. As a results, theP3HT-b-P3TPy(3/1) forms the orientated nanowires with PCBPy at the interface ofbulk heterojunction, and the average domain size is estimated to be10-20nm, whichis desirable for enlarge surface area for donor/acceptor interfaces and give a bicontinuous pathway for efficient electron transfer. Furthermore, the cooperativeassembly between P3HT-b-P3TPy and PCBPy is found to effectively suppress thePCBPy macrophase separation, and stabilize the blend morphology.Then, pyrene(Py)-functionalized diblock copolymers poly(3-hexylthiophene)-block-poly[3-(10-(pyren-1-yloxy)decyloxy)thiophene](P3HT-b-P3TPy) wastautologically synthesized. Through the noncovalent π-π stacking interactions ofpyrene groups with single-walled carbon nanotubes (SWNTs), compositeSWNTs/P3HT-b-P3TPy was obtained. The composite material has good dispersionand charge transport properties, which would be replaced of LiF as electron transportlayer in the conventional heterojunction solar cells, or to modify the defects andimprove the electronic conductivity of the ZnO in inverted polymer solar cells,eventually improving the photoelectric conversion efficiency of the device.