Synthesis And Characterization Of Novel Benzodithiophene-4,8-dione Polymers And Naphthalene Diimide Polymers For Polymer Solar Cells Application

Nowadays solar energy has attracted much attention, as one of the most promising long-term solutions for clean and renewable energy. The utilization of the photovoltaic effect to generate electricity from solar energy developed rapidly in recent years. Polymer solar cells (PSCs) have obtained considerable attention because of their low-cost, light weight, flexibility, inkjet printing process and large-area fabrication. Design and synthesis of new polymers are important for improving theperformance of PSCs. In this thesis,we synthesized a series of new conjugated polymers with broad absorption range, narrow band gap and good solubility, and used them to fabricate PSCs devices. The main results are summarized:1. Two polymers based on benzodithiophene-4,8-dione derivatives were designed and synthesized. Their optical, thermal stability, electrochemical and photovoltaic properties were studied. The LUMO levels of these polymers are-3.30eV and-2.93eV, respectively, which were lower than P3HT and were better for exciton transfer to the acceptor. So we used them as the donor to fabricate PSCs devices with PC61BM acceptor. The devices measurements revealed the best performance of power conversion efficiency (PCE) of0.028%, with an open-circuit voltage (Voc) of0.62V, a short-circuit current density (Jsc) of0.16mA/cm2. By synthesized the polymers with the same main chain but had different side chain structure, the branch side chain polymer showed better solution properties and a shorter absorbance range than the straight side chain polymer. To understand the relationship between device performances and active layer morphology, atomic force microscopy (AFM) measurements were conducted to investigate the surface morphology of active layer films. 2. Three polymers were synthesized based on N,N’-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide) as the acceptor and thienothiophene, dibenzothiophene derivative as the donors through Stille copolymerization. Their optical, thermal stability, electrochemical and photovoltaic properties were studied. Two of these polymers contained dibenzothiophene derivative units showed p-type character, and the polymer with straight side chain structurehad broad absorption range than P3HT. So we fabricated PSCs based on thesep-type polymers showed the best PCE of0.021%, with ahighest Voc of0.74V and a largest Jsc of0.12mA/cm2. The other polymer contained thienothiophene units showed n-type character, and it had better absorption in visible region than PC61BM. PSCs based on this n-type polymer showed the best PCE of0.068%, with a Voc of0.47V and a Jsc of0.29mA/cm2. By synthesized the polymers with different donor units, they showed different optical and electrochemical properties. To understand the relationship between device performances and active layer morphology, AFM measurements were conducted to investigate the surface morphology of active layer films.