Synthesis And Photovoltaic Properties Of Conjugated Polymer Containing Thiophene And Thiazole Units

Comparing with traditional inorganic photovoltaic solar cells, polymer solar cells have received focus attention since they have many advantages such as simple processing method, ultra-thin wide area with flexible substrate. The polymer solar cells can not enter into market for commercialization because their efficiency and stability can not compared with their inorganic counterpart. The absorption spectra and energy level matching 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 broad absorption band and suitable energy level for improving the photovoltaic properties of the conjugated polymers. These polymers were designed, synthesized, and characterized by 1H-NMR,element analysis and GPC, thermal, UV-Vis absorption, electrochemical properties were discussed. Bulk heterojunction polymer solar cells were fabricated based on these materials as active lays, and the photophysics of active layer, photovoltaic properties of these devices were also discussed. The main results are as follows:1. A new conjugated polymer (PBDTV) was synthesized by the Stille coupling method. The absorption spectrum of PBDTV film shows broad absorption covering the wavelength rage from 300 nm to 620 nm. Compared with other polythiophene vinylene derivatives, PBDTV has good thermal stability and photoluminescence property. HOMO and LUMO energy levels of PBDTV are -2.82 eV and -5.16 eV, respectively. When the weight ratio of PBDTV and PC71BM was 1:4, the polymer solar cell shows a high open circuit voltage of 0.71 V and the power conversion efficiency reach 2.63% under the illumination of AM 1.5, 100mW/cm2.2. Two novel alternating copolymers of thiazole with different alkyl and vinylene were synthesized. Copolymers P1 and P2 covered broad and strong absorption in visible region which are compatible with the maximum solar photon re?ux. Cyclic voltammetry experiment showed an improvement in the n-doping stability of the polymers and a reduction of their lowest unoccupied molecular orbital energy levels as a result of thiazole unit in the polymers'main chain. The highest occupied molecular orbital energy levels (HOMO) of P1 and P2 were -5.32 eV and -5.35 eV, respectively. The bulk heterojunction-typed polymer solar cells (PSCs) were fabricated with the blend of the copolymers: PC61BM=1:1 (w/w) as the photosensitive layer. Under the illumination of AM 1.5, 100 mW/cm2, the power conversion efficiencies (PCE) of the PSCs based on P1 and P2 reached 0.21% and 0.15% respectively.3. Two new donor-acceptor (D-A) alternative copolymers containing bithiazole acceptor unit and the donor unit of carbazole (P3) and dithienopyrrole (P4) were synthesized for the application as donor materials in polymer solar cells (PSCs). The donor units in the copolymers influence the bandgaps, electronic energy levels and photovoltaic properties of the copolymers significantly. The biggest absorption of P4 shows great red-shift compare with P3, from 472 nm to 540 nm. While the HOMO level changed from the -4.76 eV to -5.44 eV for P4 and P3, repectively. The polymer solar cells (PSCs) were fabricated with the blend of the copolymers: PC61BM=1:1(w/w) as the photosensitive layer. The open circuit voltages were 0.82 V and 0.28 V for P3 and P4. Under the illumination of AM 1.5, 100 mW/cm2, the power conversion efficiencies (PCE) of the PSCs based on P3 and P4 reached 0.3% and 0.06% respectively.