Synthesis And Photovoltaic Properties Of Conjugatedopolymers Based On Benzo [1,2-b: 4,5-b'] Dithiophene And Thiophene Derivatives

Polymer solar cells (PSCs) have attracted much attention due to their unique features such as low cost, light weight, and applications in large area flexible panels. So far, the most successful PSCs are bulk heterojunction (BHJ) devices. Though significant advances have been achieved in improving the power conversion efficiency (PCE) of polymer solar cells by using new active layer materials, there is still much to do before the realization of practical applications of PSCs. The limiting factors of the photovoltaic performances include the narrow absorption band, the low molar absorption coefficient, the unmatched molecular energy levels and the low charge-carrier mobility of the polymer donor materials. In this dissertation, two series of conjugated polymers based on benzo[1,2-b:4,5-b']dithiophene (BDT) and thiophene derivative, containing electron-withdrawing units in the side chain, were designed and synthesized. These polymers are novel donor-acceptor (D-A) conjugated polymers with electron-donor units in the main chains and electron-acceptor units in the side chains. These polymers were characterized by 1H-NMR,13H-NMR, FT-IR, and MALDI-TOF MS, and the photophysical, electrochemical and photovoltaic properties of the as-synthesized polymers were investigated by Uv-Vis absorption spectra, Cyclic voltammetry and J-V curves. The main results are as follows:1. Six alternating conjugated copolymers (PL1-PL6) of benzo[1,2-b:4,5-b']dithiophene (BDT) and thiophene derivatives, containing electron-withdrawing oxadiazole (OXD), ester or alkyl as side chains, were designed and synthesized by Stille coupling reaction. The results indicate that the introduction of conjugated electron-withdrawing OXD or formate side chain can benefit to broaden the absorption band, decrease the bandgaps of the polymers and improve the photovoltaic performance. BHJ PSCs were fabricated based on the blend of the as-synthesized six copolymers and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) in a 1:2 weight ratio. Under simulated AM 1.5G solar irradiation (100 mW/cm2), the devices based on PL3 and PL5 showed maximum power conversion efficiency of 1.98% and 2.06%, respectively.2. The polymers (P1-P4) were synthesized by Stille coupling reaction at 4- and 8-positions of BDT. The new D-A conjugated polymers contain BDT in main chains and different electron-withdrawing groups, including formal or diethyl 2-vinylmalonate as side chain. The results indicate that the tacticities of the polymers should be destroyed if the formal groups are not completely reacted, which leads to the blue-shifted absoption, the increase of the bandgap, and the inferior photovoltaic performance. The maximun PCE of the cell based on P1 is 0.35% under the irradiation of AM 1.5,100 mW/cm2.