Photopolymerization Initiated By One-dimensional Semiconductor Arrays And The Preparation Of Photovoltaic Devices

Owing to the rapid consumption of the traditional fossil fuels in the world, it is very urgent to find alternative energy resources. As one of the technologies for utilizing new energy, the photovoltaic solar cells which can convert the solar light energy into the electrical power have become the subject of great significance. Among various types of the solar cells, the hybrid photovoltaic devices based on the conjugated polymers and inorganic semiconductors have attracted much attention due to the fact that the hybrid devices combine the flexibility of the polymers with the relatively high electron-mobility of the inorganic semiconductors. Inspired by the good performances of the bulk-heterojunctions which are based on the conjugated polymers and fullerene derivatives, many researchers have paid attention on the bulk-heterojunctions of the conjugated polymers and inorganic semiconductors, in effort to replace the electron-acceptor fullerene derivatives with the nanoscale semiconductors including TiO2and ZnO nanoparticles. In the case of using the conventional semiconductor nanoparticles, however, the electrons transport through jumping across the nanoparticles’ films and as a result, the possibility of charge-recombination is considerable high. Moreover, the loose contact between the nanoparticles and the electrode always shows a negative influence on the efficiency of the charge collection. Another problem which is encountered with the hybrid devices is the chemical incompatibility between polymer and inorganic nanostructures, which usually leads to poor charge-separation and low energy-conversion efficiency.One-dimensional semiconductor nanoarray can provide a direct path for electron transport. Meanwhile, the nanoarray can grow on the electrode and thus, the nanoarray is combined with the electrode. So, one-dimensional nanoarray is regarded as an ideal candidate for the electron-acceptor in the heterojunction solar cells. Photocatalytic polymerization is initiated by photoexcited nanocrystals and polymer formed by this technique is in good contact with the inorganic semiconductor. Conjugated polymer/inorganic semiconductor composites which are prepared by this technique can overcome the issure of incompatibility which exists in the traditional physical blending.Basing on the concepts as above, this work carries out the polymerizations by using the one-dimensional inorganic semiconductors as the initiators, with the aim to prepare with the desirable composites consisting of the conjugated polymer and the one-dimensional semiconductors. Furthermore, the optical, electrical properties of the synthesized composites are investigated. The interfaces between the semiconductors and polymers are studied in order to explore whether our photocatalytic polymerizations have improved the charge transfer and charge separation. The contents and fruits of the thesis are as follows:1. ZnO nanorod array films with good morphology are prepared by electrochemical deposition method. XRD results show that the obtained ZnO nanorod array is wurtzite phase. The nanorod arrays are used in photo-initiated polymerization of NVK and the PVK/ZnO composite film is obtained.2. TiO2nanorod array films are synthesized by hydrothermal method. XRD and Raman spectra show that the obtained TiO2nanorod arrays are rutile phase. The TiO2nanorod arrays are used to degrade organic compounds and generate hydroxyl radicals to evaluate the photocatalytic activity. The results show that the prepared TiO2nanorod arrays have good photocatalytic activity.3. The TiO2nanorod arrays are used in photocatalytic polymerization of pyrrole and the PPy/TiO2nanocomposite films are obtained. Raman spectra show that the thickness of the PPy can be controlled through the photopolymerization time. XPS results show that there is a strong interaction between PPy and TiO2. Further, the rutile TiO2nanoparticles are used in photo-initiated polymerization of pyrrole to prepare PPy/TiO2nanocomposite for the EPR measurement. EPR results confirm that there is effective charge transfer between PPy and TiO2.4. Photovoltaic devices are fabricated with PPy/TiO2composite films through photo-initiated polymerization.5. Photocatalytic polymerization is used to improve the interfacial properties of the organic/inorganic solar cells by using P3HT and TiO2as a model. The surface of the TiO2nanorods is modified with polypyrrole via photocatalytic polymerization. The P3HT/PPy/TiO2and P3HT/TiO2films are prepared by spin-coating and used to fabricate solar cells. TRPL results indicate that the PPy improves the electron injection from P3HT to TiO2. The results from IMVS and EIS consistently prove that the grafted PPy significantly retards the charge recombination. The power conversion efficiency of the P3HT/PPy/TiO2device is enhanced by77%as compared to the unmodified, P3HT/TiO2device.