Preparation Of Polythiophene/ZnO Nanocrystal Bulk Heterojunction Hybrids For Photo-electricity Devices

Conjugated polymers (CPs) are promising materials for application as light-absorbing and charge-transporting components in low cost photovoltaic devices because of their good properties such as cheap cost, good mechanical flexibility, and easy chemical tailoring. However, rapid recombination of photogenerated excitons and the poor charge carrier mobility in most conjugated polymers limit the maximum efficiency (ECE) of the photovoltaic cells. This problem has been resolved, in part, by incorporating inorganic nanocrystals with higher electron affinity into the polymer.The current techniques for making conjugated polymer/nanocrystals composite materials rely upon synthesizing nanocrystals respectively, and mixing them with conjugated polymer. This approach has some shortcomings. To control nanocrystals growth and facilitate their dispersion, surfactant is often introduced into reaction system. Some of the surfactant will be coated around the nanocrystals, which inhibits efficient charge transfer. Moreover, the mixing approach requires the use of co-solvents, which can adversely affect nanocrystals solubility and polymer chain orientation.To improve the distribution of nanocrystals in the conjugated polymers, application of surfactants is a conventional method. Although the capping of surfactants on inorganic nanocrystals can obtain well-dispersed nanocomposites, the nanocomposites are just simple physical mixtures and the interaction between surfactants or ligands and nanocrystals is static and weak, such as van der Waals' forces, or Lewis acid-base interactions, which will be affected by the process and use conditions, leading to the properties of nanocomposites unstable. Compared with physical capping, chemical surface modification of inorganic nanocrystals is more stable because of the strong covalent bond between the components. Up to now, many studies have been carried out about bonding polymers and nanostructured materials chemically. Their results all showed that the inorganic nanocrystals modified by polymers chemically possess stable luminescence, good dispersion in organic solvents and excellent compatibility with the polymeric matrix. In this study, the ZnO nanocrystals whose surface were bonded by copolymer shell with the internal hydrophobic polymethacrylate layer and the external hydrophilic poly(ethylene glycol) methyl ether groups were prepared by a simple sol-gel method. Because of bonding the copolymer shell on the surface of ZnO nanocrystals, the dispersion of ZnO nanocrystals has been improved greatly. Meanwhile, the particle size of ZnO@PPEGMA becomes smaller than that of ZnO due to the presence of copolymer shell, resulting in the blue-shift of absorbance edge and UV PL emission of ZnO.Meanwhile, It has been reported that conjugated polymer/nanocrystals composite materials can be prepared by firstly introducing metal ion into conjugated polymer and then obtaining inorganic CP/nanocrystals blends by hydrolysis in situ. Conducting polymers with functioned groups can act as self-assembling complex polymer to control disperse and crystal growth of inorganic nanocrystals. It shows the method successfully control the growth and dispersion of inorganic nanocrystals in CPs without introduction of any surfactant.In the paper, we report a new approach to synthesize poly(thiophene) grafted poly(methacrylate)/ZnO (PTh-g-PMA/ZnO) hybrids through atom transfer radical polymerization (ATRP) and hydrolysis in situ. The new method we describe has two major advantages. The PTh-g-PMA/ZnO hybrids were prepared by in-situ hydrolysis of poly(thiophene) grafted poly(zinc methacrylate) (PTh-g-PZMA) casting films. In the resulting nanocomposite films, ZnO nanocrystals were homogeneous dispersed in the hybrids because of the template function of PTh-g-PZMA precursor, without evident macrophase separation, indicating excellent compatibility and a large interfacial area between poly(thiophene) and ZnO nanocrystals. A maximum of 85% of the fluorescence quenched for PTh-g-PMA/ZnO.