Preparation And Optimization Of Low Bandgap Polymer Based Organic Solar Cells

Clean and renewable energy is an inevitable choice in the context of energy crisis and environmental pollution. As one of them, solar energy has been highly respected because of its advantages of volume, wide distribution and various ways to utilize such as photothermal and photovoltaic. Solar cells are devices that convert sunlight into electricity to store and apply. Currently, solar cells used in practical are almost inorganic solar cells, but their high cost, complex process, limited material and possible pollution restrict their large-scale application. Organic solar cells have caused increasingly research interest due to their sufficient material, low cost, simple preparation, broad market and possible flexibility with large area.In this thesis, PTB7:PC71BM based organic bulk heterojunction solar cells with conventional and inverted structures have been prepared using spin-coating and vacuum thermal evaporation, and their efficiency and stability have been compared. It is found that, although the power conversion efficiency of the inverted organic solar cells is slightly worse, only 84.86% of that of the conventional devices, the inverted organic solar cells have better device stability. The inverted organic solar cells remain more than 90% of its original PCE value, after all devices placed in nitrogenous glove box for 25 days without encapsulation, while the conventional devices only 75%. The influence of cathode buffer layer annealing in nitrogenous atmosphere, the oxygen plasma treatment and the time the organic active layer used to dry on inverted organic solar cells has been studied to further improve the performance of the inverted organic solar cells. It is found that cathode buffer layer annealing in nitrogenous atmosphere can significantly enhance device efficiency. The analysis on AFM surface morphology and UV-Vis transmittance spectra indicates that the Zn O thin film annealing in nitrogenous atmosphere has smaller surface roughness and higher charge mobility, so there is more efficient carrier transport and collection; The effect of oxygen plasma treatment on ITO layer on device performance is not obvious,since it decreases the JSC and FF while increases the VOC of the solar cells; Eight hours’ drying time of the organic active layer is optimal, since too long or too short odrying time will result in serious light-soaking phenomenon.The obtaining of the inverted organic solar cells with high efficiency and good stability by choosing inverted device structure, changing the annealing atmosphere and optimizing the drying time makes us believe the possibility and inevitability to achieve efficient and stable organic solar cells, but to realize large-scale industrialization of organic solar cells requires researchers’ continuous exploration and efforts through extensive exchange and cooperation.