Synthesis And Study On The Properties Of Copolymer Photovoltaic Materials Based On Benzo[1,2-b:4,5-b’]dithiophene And Diketopyrrolopyrrole

Polymer solar cells (PSCs) have been attracted much attention due to itscommercial competitiveness, such as low cost, flexible substrates, light-weight. Withthe joint efforts from all social sectors, great progress has been achieved with thehighest power conversion efficiency (PCE) over10%. Although the progresses havebeen impressive, there are still many difficulties need to be overcome before therealization of the practical applications of PSCs. In order to obtain conjugatedpolymers with ideal properties, such as broad and strong absorption spectra,appropriate HOMO and LUMO energy levels, high hole mobility, we designed andsynthesized a series of random copolymers that comprise electron-richbenzodithiophene (BDT) or alkylthienyl-substituted benzodithiophene (BDTT) unit inconjugation with diketopyrrolopyrrole (DPP) moiety and the units containingisoindigo (TID) or benzothiadiazole (TDTBT) on side chain of copolymers. Thestructures of the intermediate and copolymers were confirmed by1H-NMR, FT-IR,MALDI-TOF, and13C-NMR. The electrochemical and photophysical properties of theas-synthesized copolymers were systematically investigated by cyclic voltammetryand UV-Vis-IR absorption spectra. Bulk heterojunction (BHJ) solar cells based on thecopolymers as electron donors and (6,6)-phenyl-C61-butyric acid methyl ester(PC61BM) as acceptor were fabricated. The main results are as follows:1. Two novel random conjugated terpolymers P1and P2with twoelectron-deficient units, DPP and TDTBT, were synthesized for PSCs. UV-Vis-IRmeasurements revealed that the absorption spectra of the random terpolymers weresignificantly broadened after incorporating the two chromophores. Meanwhile, thefrontier energy levels and band gaps were fine-tuned by combining twoelectron-deficient into the random terpolymers backbones. The test results showedthat the random terpolymers exhibited a promising application in BHJ solar cells withbroad absorption spectra, appropriate HOMO and LUMO energy levels, and their lowenergy band-gaps. PSCs based on all presented copolymers as donors and PC61BM asacceptors were fabricated. Compared with binary alternating analogues, the twoterpolymers, P1and P2exhibited the improved the PCE of5.05%and4.85%respectively.2. A series of random terpolymers with BDTT as donor and two electron-deficient DPP and TID as acceptor were synthesized to obtain polymers withbroad and complementary absorption range from300to900nm for PSCs. Observedfrom the UV-Vis-IR measurements, the absorption spectra of the terpolymers weresignificantly tuned by varying the composition of DPP to TID in the sturctures of thepolymers. P5, which with the equal content of DPP and TID, increased the efficiencyto5.62%due to its improved light absorption spectura and thus a Jscvalue higher than15mA cm-2.