Synthesis And Characterization Of Narrow Band Gap Polymer Photovoltaic Materials

The absorption spectra and hole mobility of conjugated polymer donor materials are the major factors to affect the power conversion efficiency (PCE) of polymer solar cells (PSCs). This dissertation is focusing on the design and synthesis of new conjugated polymers with broader absorption band and higher hole mobility for improving the photovoltaic properties of the conjugated polymers. The main results are as follows:(1) A new polythiophene derivative with octyl diphenylamine-vinylene conjugated side chain was synthesized by the Stille coupling reaction, and characterized by 1H NMR, GPC, TGA, UV-Vis absorption spectroscopy, and cyclic voltammetry. DPAV-PT possesses a broad absorption band at 300-650 nm. Polymer solar cell with the configuration of ITO/PEDOT:PSS/DPAV-PT:PCBM(1/1, w/w)/Ca/Al demonstrates the power conversion efficiency of 0.7% under the illumination of AM 1.5G,100 mW/cm2. The field effect hole mobility of the polymer reached 6.1×10-4 cm2/Vs with an on/off ratio of 103 and threshold voltage of-7 V after 180℃annealing.(2) Two new low bandgap black copolymers derived from dithienylbenzothiadiazole (DTBT) and different electron-rich functional groups (dioctoxyl benzene and N-octyl-diphenylamine) were synthesized by Heck cross-coupling polymerization. DSC and TGA results indicate that the copolymers possess good thermal stabilities. PPV-DTBT and DPAV-DTBT films exhibit broad absorption bands at 300-765 nm and 300-733 nm, respectively. Preliminary photovoltaic cells based on the composite structure of ITO/PEDOT:PSS/PPV-DTBT:PC60BM(1/2, w/w)/Al showed an open-circuit voltage of 0.75 V, a power conversion efficiency of 0.6% and a short circuit current of 1.7 mA/cm2.(3) A series of new isoindigo-based conjugated polymers were synthesized by Stille or Suzuki coupling reaction. The polymer films exhibit a broad absorption bands in the wavelength range from 300-800 nm. Especially, PBDTID possesses the smallest bandgap of 1.55 eV calculated from its absorption band-edge at 800 nm. These results show that isoindigo-based donor-acceptor copolymers are promising broad absorption and low bandgap materials for developing efficient bulk heterojunction solar cells.