| Polymer solar cells (PSCs) have attracted considerable attention in recent yearsdue to their potential for low cost, lightweight, and good compatibility with theroll-to-roll process for making flexible large area devices. In the efforts of researchers,the PCE of BHJ PSCs has achieved10%. However, to realize the real commercialproduction, there are still some challenges. In order to broaden the absorption band,enhance the charge carrier mobility, and tune the HOMO and LUMO enery levels ofpolymer photoconductive materials, we have designed and synthesized a series of newconjugated polymers containing4,7-dithien-5-yl-2,1,3-benzodiathiazole (DTBT) sidegroups. The structures of the as-synthesized polymers were all confirmed by1H-NMR,13C-NMR, FT-IR and MALDI-TOF. The photophysical and electrochemicalproperties of the polymers have been investigated systematically by UV-vis spectra,PL spectra, and Cyclic Voltammetry. In addition, the photovoltaic performances ofsolar cells based on the as-synthesized polymers were measured. The main results areas follows:1. A new benzodithiophene-based copolymer PTG1with dithienyl–benzothiadiazole–vinylene side chains has been designed and synthesized.4,7-dithien-5-yl-2,1,3-benzodiathiazole (DTBT) moiety as an electron-deficient unit isfor the first time to be introduced as side chains attaching the main chain of thepolymer via vinylene group. The effect of DTBT side chain on the thermal, optical,electrochemical and photovoltaic properties have been investigated. PTG1exhibitsexcellent film forming ability, a deep HOMO energy level, and a good miscibilitywith PC71BM. Bulk heterojunction polymer solar cells fabricated from PTG1andPC71BM showed a promising power conversion efciency of4.32%.2. Three novel copolymers (PT-ID, PT-DTBT and PT-DTBTID) ofbenzo[1,2-b:4,5-b’]dithiophene and thiophene with different conjugated side groups(1,3-indanedione (ID),4,7-dithien-5-yl-2,1,3-benzodiathiazole (DTBT), andDTBT-ID) were synthesized and developed for polymer solar cell applications. Theeffects of the different conjugated side groups on the thermal, photophysical,electrochemical and photovoltaic properties of these copolymers were investigated.As the length of the conjugated side groups increased, the absorption of the UV-visregion in solution was red-shifted. By changing the different side groups, the energy levels and band gaps of the resulted copolymers were effectively tuned. The threecopolymers exhibit deep HOMO energy level and relatively high open-circuit voltage(Voc). Bulk heterojunction solar cells with these copolymers as electron donors and(6,6)-phenyl-C61-butyric acidmethyl ester (PC61BM) as an electron acceptor exhibitpower conversion efficiencies of2.48%,4.18%and1.16%for PT-ID, PT-DTBT andPT-DTBTID, respectively.3. A series of novel low band gap polymers containing conjugated side chainswith4,7-dithien-5-yl-2,1,3-benzodiathiazole and different electron-withdrawing endgroups of aldehyde (PT-DTBTCHO),2-ethylhexyl cyanoacetate (PT-DTBTCN), and1,3-diethyl-2-thiobarbituric acid (PT-DTBTDT), and electron-donating end group of2-methylthiophene (PT-DTBTMT) have been designed and synthesized. All polymersexhibit good solubility in common organic solvents, film-forming ability and thermalstability. These conjugated polymers show the broad UV–vis absorption and thenarrow optical band gaps in the range of1.65-1.82eV. Through changing the endgroup of conjugated side chains, the photophysical properties and energy levels of thepolymers were tuned effectively. Bulk heterojunction solar cells based on the blend ofthese polymers and (6,6)-phenyl-C61-butyric acid methyl ester (PC61BM) reached thebest power conversion efficiency (PCE) of2.72%. |
