Synthesis Of D-A Type Organic Small Molecule Photovoltaic Materials And Investigation Of The Relationship Between Molecular Structure And Properties

Since 21 century, people have devoted to develop new the clean and sustainable energy source because of the increasing scarcity of fossil energy and the increasingly serious environmental pollution. Organic photovoltaics(OPVs) have became a key direction of new energy source development and application in recent years for their unique advantagies such as clean, no pollution, without geographical restriction, light weight, flexibility in large area applications and inexhaustible. In particular, small molecules(SMs) based OPVs, because of their advantages such as wide material sources, defined molecular structure, no batch-to-batch difference and good repeatability and so on, have been favored by researchers and photovoltaic companies. In this dissertation, we systematically introduced the development of OPVs and their working principles, as well as their dornor and acceptor materials in active layer. In order to solve the existing problems of OPVs such as the relatively low power conversion efficience(PCE) that can’t meet the demand of commercial production, less variety of high-performance donor materials, ambiguous the relationship between molecular structure and property, a seriers of donor(D)-acceptor(A) type SMs based on diketopyrrolopyrrole(DPP) and benzothiadiazole(BT) were designed and synthesized. Their molecular structures were characterized. Their thermal stability, and photophysical, electrochemical properties, as well as their photovoltaic performance in bulk heterojunction(BHJ)-OPVs were systematically investigated. The relationship among molecular structures and these performances were further summarized. And some high-performance photovoltaic D-A type SMs were obtained. The key studies are listed as follows:1. Three classes of D-A, D-A-D and D1-A-D-A-D1 types low band-gap SMs used as photovoltaic donor materials were designed and synthesized, in which triphenylamine, carbazole, thiophene and phenanthrene were used as terminal D groups, DPP derivatives were used as A groups, 9,10- and 2,6-anthracene as well as 1,6- and 2,7-pyrene were used as central D groups. The effect of molecular configuration, the central D groups and their linkage position, and the termianal D groups on photovoltaic performance was systematically studied. It was found that SM of ThDPP2Py(2,7) with 2,7-pyrene and 2-octylthiophene as central and terminal unit, rexhibited better photovoltaic properties. The maximum power conversion efficiency(PCE) of 5.88% with a short circuit current(Jsc) of 15.35mA/cm2, an open circuit voltage(Voc) of 0.66 V and a fill factor(FF) of 57.89% was obtained in the ThDPP2Py(2,7)-based BHJ-OPVs.2. A class of A-D-A type low band-gap SMs based on DPP with different alkyl chain length as A unit and 2,7-pyrene as central D unit were designed and synthesized. The influence of alkyl chain length on photovoltaic performance was systematically investigated. It was demonstrated that the SM of C8-DPP2 Py with shortest alkyl chain exhibited better photovoltaic performance than others in BHJ-OPVs. The maximum PCE of 5.67% with a Jsc of 11.13mA/cm2, a Voc of 0.85 V and a FF of 60.07% was obtained in the C8-DPP2Py-based BHJ-OPVs.3. A class of A-D-A type low band-gap SMs based on 3-octyloxybenzene or 4-fluoro-3-octyloxybenzene substituted benzodithiophene as central D unit and N-alkylated or O-alkylated DPP as A group were designed and synthesized. The effect of fluorine substitution and isomerization of DPP on photovoltaic performance was systematically investigated. It was shown that the SM of POFPBDT-2DPP with 4-fluoro-3-octyloxybenzene substituted benzodithiophene and N-alkylated DPP as central D and terminal A unit exhibited better photovoltaic performance in their BHJ-OPVs. The maximum PCE of 3.15% with a Jsc of 8.33mA/cm2, a Voc of 0.95 V and a FF of 39.60% was obtained in the POFPBDT-2DPP based BHJ-OPVs.4. A novel penta-heterocyclic building block of benzodi(pyridothiophene)(BDPT) and its three SMs based on DPP and BT derivatives as terminal A unit were designed and synthesized. It was shown that the SM of BDPT-2DPP based on BDPT and DPP units exhibited better photovoltaic performance in their BHJ-OPVs. The maximum PCE of 3.97% with Jsc of 9.00 mA/cm2, Voc of 0.84 V and FF of 52.37%, was obtaind in the BDPT-2DPP-based BHJ-OPVs.5. Two classes of A-D-A and D1-A-D-A-D1 types SMs used as photovoltaic donor materials were designed and synthesized, in which carbazole and phenanthrene were used as terminal D groups, BT derivatives were used as A groups, 2,7-pyrene were used as central D groups. The effect of the molecular configuration and intramolecular non-covalent bond interaction on photovoltaic performance was systematically investigated. It was shown that the SM of Py-2DTBTCz based on carbazole and BT exhibited better photovoltaic performance in their BHJ-OPVs. The maximum PCE of 2.89% with Jsc of 7.68 mA/cm2, Voc of 0.99 V and FF of 37.81%, was obtaind in the Py-2DTBTCz-based BHJ-OPVs.