Synthesis And Properties Of D-A Type Narrow Bandgap Conjugated Polymers Containing Diketopyrrolopyrrole

The increasing serious global energy problems force people to develop new types of clean and sustainable energy. Harvesting energy directly from sunlight using photovoltaic technology is considered as being one of the most important ways to solve the problem. Solar cells can be divided into two different categories:organic solar cells and inorganic solar cells. At present, crystalline silicon based photovoltaic technology plays a important role in the market. However, there are several drawbacks such as the high cost, high purity materials and complex.manufacturing process limiting its further development. Owing to its advantage of low cost, flexible, light weight and large area applications, Organic polymer solar cells (OSCs) attracts widely attention. The conventional polymer solar cells are made with polythiophene derivatives as the donor material, which may achieve an efficiency surpassing5%. However, the bandgap of polythiophene derivatives is between1.9-2.0eV, only to absorb the wavelength of below650nm, which results to not making best of the most energy of sunlight. In order to expand the absorption spectrum and improve the efficiency of solar cells, narrow bandgap conjugated polymers have attracted great interest. Among them, diketopyrrolopyrrole (DPP) based polymers have received the widespread attention because of their lower bandgap.good coplanarity and strong electron withdrawing.The research status of the diketopyrrolopyrrole (DPP) based donor materials and their organic solar cells were summarized in this dissertation.In the first chapter,in order to narrow the bandgap, thiophene-DPP was evaluated as the donor material in the D-A copolymers (P1and P2). Inserting furan moieties into the backbone of the conjugated polymers can improve their solubility. In the second chapter, furan-DPP was selected as the donor material in the D-A type narrow bandgap conjugated polymers (P3and P4). Direct arylation of polymerization method was used to synthesize the four polymers, such polymerization method has the advantage to avoid environmental pollution and reduce the synthesis time.The structure, molecular weight, polydispersity and thermal stability of the four polymers were characterized by FT IR,1H NMR, GPC, TGA and DSC. The photophysical properties of the polymers were analysized by fluorescence spectroscopy, UV-Visible absorption spectroscopy and cyclic voltammetry (CV).The result shows that such polymers are all low-bandgap copolymers. The bandgap of these four copolymers is1.76eV,1.72eV,1.61eV and1.78eV, respectively. TG results show that the thermal stability of the four copolymers is good. UV-Visible absorption spectroscopy studies show that the copolymer containing DPP can broaden the absorption spectrum better, and the absorption edge is reached around850nm, which is helpful to improve the photoelectric conversion efficiency directly.