Synthesis And Photovoltaic Properties Of D-A Conjugated Polymers Based On Triazole

Bulk-heterojunction polymer solar cells have widely studied as the solarenergy-electrical power transforming devices for the potential advantages of preparingflexible and lightweight devices by roll-to-roll solution processing. In the past few years, thesignificant improvement of the power conversion efficiencies of polymer solar cells has beenachieved for the great progresses on the novel high-performance photovoltaic materials anddevice optimizations. And now, the maximum power conversion efficiency has been over8.0%. However, there is still much to do before realizating practical applications of PSCs. Thepower conversion efficiencies of PSCs are obviously affected by the absorption spectra, thehole mobility and soluble property of the photovoltaic materials. In order to improve theabsorption spectra and the hole mobility of the polymers, two series of conjugated polymersbased on1,2,4-triazole were designed and synthesized. Those polymers were characterized by1H NMR,13C NMR and GC-MS, and the photophysical, electrochemical and photovoltaicproperties of the as-synthesized polymers were investigated by Uv-Vis absorption spectra,fluorescence emission spectrum, cyclic voltammetry and J-V curves. The main results are asfollows:1. Three novel conjugated polymers PT-TZ, PB-TZ, and PB-TTZT, contained withelectron-deficient1,2,4-triazole in the backbone, were designed and synthesized by Stillecoupling reaction. The copolymers, comprised of1,2,4-triazole with different electron-richgroups, show different photophysical, electrochemical and photovoltaic properties. Whencomprised by different electron-rich groups, the HOMO levels and the LUMO levels can beadjusted. When the backbone of the polymer was comprised by more thiophene units, theconjugation length of the polyners could increase, and the absorption spectra of the polymerswere broaden. As a result, the PCE value of the PSC based on polymer PB-TTZT is higherthan that of the other polymers. The maximum PCE of the PSC based on the polymerPB-TTZT as the donor and PC61BM as the acceptor was1.18%under the simulated AM1.5Gsolar irradiation (100mW/cm2).2. Three novel soluble alternating conjugated polymers PT-TZN, PF-TZN, andPBDT-TZN, comprised of thiophene, fluorene, benzo[1,2-b:4,5-b’]dithiophene and thiophenederivatives with3-nitro-1,2,4-triazole side chains, were synthesized via thepalladium-catalyzed Suzuki coupling reaction or Stille coupling reaction. The introduce of3-nitro-1,2,4-triazole side chain is benefit to decrease of the bandgap of the polymer. However,it would lead to the intermolecular excimer and the de-excitation of partial excitions which are detrimental to the power conversion because the electron-withdrawing of nitro group istoo strong. Photovoltaic cells have been fabricated with the as-synthesized polymers as thedonor and PC61BM as the acceptor in a1:3weight ratio. Under the simulated AM1.5G solarirradiation (100mW/cm2), the device based on PBDT-TNZ showed the power conversionefficiency of1.13%.