Synthesis And Photovoltaic Properties Of D-a Type Organic Donor Materials Based On Benzodithiophene And Triphenylamine

Organic solar cells(OSCs) have been become an important area of developing new energy sources owe to their low cost, light weight, flexibility, friendly environ-ments. In this dissertation, the current developing status of OSCs and their donor materials are reviewed. In order to solve the key issue of low power conversion efficiency(PCE) for OSCs, the molecular design and synthesis and properties of photovoltaic polymers and small molecules(SMs) were developed. As a result, a series of D-A type photovoltaic polymers and SMs were obtained. Their optical, electrical, thermal properties and photovoltaic performances were systematically investigated. The works contain mainly three aspects as follow:1) A class of the novel D-A type copolymers of PBDTDT(Qx-2)-O and PBDTDT(Qx-2)-T were designed and synthesized, in which alkoxy or thienyl substituted benzo[1,2-b:4,5-b’]dithiophene(BDT-O or BDT-T) are used as donor(D) unit, and 2,3-di(4-methoxyphenyl)-6,7-dioctyloxy-quinoxaline(Qx-2) is employed as acceptor(A) unit. The influence of the substitute group in benzo[1,2-b:4,5-b’]dithiophene(BDT) and 6,7-dioctyloxy in quinoxaline on photovoltaic properties of their polymers were investigated. Compared to the reported analogues, both one-dimensional(1D) copolymer of PBDTDT(Qx-2)-O and two-dimensional(2D) copolymer of PBDTDT(Qx-2)-T exhibited outstandingly increasing open-circuit voltages(Voc) about 0.91 ~ 0.95 V in the bulk-heterojunction(BHJ) polymer solar cells(PSCs), while 6,7-dioctyloxy group was appended in quinoxaline. The maximum PCE of 6.31 % with Voc of 0.95 V, short-circuit current(Jsc) of 10.82 mA cm-2 and fill factor(FF) of 61.4% was obtained in the 2D conjugated copolymer of PBDTDT(Qx-2)-T/PC71 BMbased device. The PCE value is 1.42 times higher than that of the 1D-conjugated polymer of PBDTD(Qx-2)-O/PC71BM-based device.2) A novel side-chain D-A conjugated copolymer of PDPTA-BDT-BT was designed and synthesized, which contains binary donor units of N,N-diphenylthiophen-2-amine(DPTA) and BDT in main chain and the pending acceptor unit of benzothiadiazole(BT) in side chain. Compare to its counterpart of PDPAT-BDT-BT with an additional phenyl spacer between the DPTA and BT units, this PDPTA-BDT-BT exhibited smaller optical band-gap, broader absorption range and lower HOMO energy level(-5.43 eV), as well as improved photovoltaic properties in the BHJ-PSCs. The maximum PCE of 3.27 % with a Voc of 0.87 V and a FF of 49.8% were obtained in the PDPTA-BDT-BT-based cells. Our work indicates that the photophysical and photovoltanic performances of the side-chain D-A polymers can be significantly improved by shortening spacer between D and A units in PSCs.3) A type of “C3” symmetrical star-shaped SMs of P(TAT-DPP-T)3 and P(TATDPP-TPA)3 were designed and synthesized, in which 1,3,5-substituted phenyl as the central core, 9,10-di(2-thiophene)anthracene(TAT) as the polycyclic arene π-bridges, diketopyrrolopyrrole(DPP) as the acceptor arms, triphenylamine(TPA) and thiophene as the donor terminal. Compared to the previous analogues, these SMs add the TAT π-bridge and the terminal of TPA or thiophene. Their UV-Vis absorption, electrochemistryand thermal stability and hole mobility were investigated prelininary. Significantly red-shifted UV-Vis absorption spectra were observed for P(TAT-DPPTPA)3 instead of P(TAT-DPP-T)3. As result, the P(TAT-DPP-TPA)3/PC71BM-based SM-OSCs exhibited an improved PCE of 1.26% compared to P(TAT-DPP-T)3/PC71BM-based SM-OSCs with a PCE of 1.14%.