| Along with the world’s societies develop, the energy reserve is rapidly reducing. The development and utilization of new and renewable clean energy have become one of the major focus in the world. Because of its clean and pollution-free characteristics, solar energy has attracted the attention of scientists and government. Reasonable development and utilization of the solar energy resources can effectively reduce the pressure on fossil energy, therefore it shows an important practical significance. Polymer solar cells(PSCs), with its advantages of low-cost, light-weight, flexibility and reel-to-reel coating applied in large area, have attracted substantial interest and investigation in recent years.This thesis mainly focuses on poly(3-hexylthiophene)(P3HT):[6,6]-phenyl-C61 butyric acid methyl ester(PCBM) and poly(3-hexylthiophene)(P3HT):indene-C60 bisadduct(ICBA) which are served as electron donors and receptors of active layer material to value the physical property of the solar cells. Firstly, the influence of electric field treatment on PSCs performance is investigated based on the polarity of polymer materials and morphology of the active layer. Then, the impact of electrode geometry on the performance of PSCs is also analyzed. Finally, a series of P3HT:ICBA bulk heterojunction PSCs with different cholesteric liquid crystalline(LC)-cholesteryl chloride doping concentrations are discussed.Firstly, a ferroelectric field effect in the bulk heterojunction was found when an external electric field was applied on the active layer of the polymer solar cells during the annealing process of the active layer made of P3 HT and PCBM. For one direction field, the short circuit current density of PSCs was improved, and the power conversion efficiency also increased. External electric field treatment can orientate the molecular ordering of the polar PCBM, and change the morphology of the active layer. It shows that the ferroelectric field has been built in the active layer which proves that the field plays a key role in PSCs system.Secondly, the impact of electrode geometry on the performance of PSCs is investigated. The negative electrodes with equal area but different shape(round, oval, square and triangular) are evaluated with respect to short-circuit current density, open-circuit voltage, fill factor and power conversion efficiency of PSCs. As a conclusion, the electrode boundary curvature has a significant impact on the performance of PSCs. The larger curvature, i.e. sharper electrodes edges, has a negative effect on exciton separation and carrier transport in photoelectric conversion processes.Finally, a series of P3HT:ICBA bulk heterojunction PSCs is fabricated by doping cholesteric liquid crystalline(LC)-cholesteryl chloride with different concentrations. From the micro molecular configuration and macro device performance, aspects of the cell characteristics such as the active layer and molecular arangement, film morphology, optical properties, and so on are analyzed.As a conclusion, for the electric field treatment on the active layer, one direction field can result in the short circuit current density of PSCs to have an improved from 7.2 to 8.0 mA/cm2, the power conversion efficiency to increase from 2.4% to 2.8%, and the incident photon-to-current conversion efficiency to increase from 42% to 49%. For the impact of electrode geometry on the performance of PSCs, the results show that the device with round electrodes gives the best photovoltaic performance; in contrast, the device with triangular electrodes reveals the worst properties. A maximum difference of almost 19% in power conversion efficiency with a round electrode and with triangular electrode is obtained. For liquid crystal doping, it shows that the open circuit voltage is increased from 0.65 V to 0.78 V, almost a 10% increase in power conversion efficiency when the doping concentration is 5.0%.The researcher expect the work to provide a meaningful reference value for the polymer solar cell research and its manufactured process. |
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