Synthesis And Study On The Photovoltaic Properties Of Organic Materials Containing Diketopyrrolopyrrole And Isoindigo Derivatives

Solar energy has attracted extensive attention by the world due to the advantagesof widely used, environmental friendly and inexhaustible. Currently solar cells basedon silicon have been used in reality, but due to its high cost and environmentalpollution limit its wide range of applications. Organic solar cells (OSCs) haveattracted attention in academica due to the advantage of light weight, low cost,flexible and large area production. While the active layer of organic solar cell isgenerally made of electron-donating organic materials and high-electron-affinityfullerene derivatives, and the electron-donating organic materials which consist ofelectron-donating donor unit (D) and the electron-affinity acceptor unit (A) have beendeveloped widely. The diketopyrrolopyrrole (DPP) unit and isoindigo derivativeshave been widely used in OSCs due to its broad and strong absorption in theUV-visible. We successfully designed and synthesized three small molecules basedon DPP core with different terminal groups, also designed and synthesized a new π-extended isoindigo derivative, and applied in small molecule bulk heterojunction(SMBHJ) solar cells. We investigated the structural characterization and photovoltaicperformance of the small molecules, and the results as follows:1. We synthesized three new low bandgap donor-acceptor-donor (D-A-D) typeorganic small molecules (M1-M3). Small molecules consisting of naphthaleneend-groups and DPP (M1and M3) and one reference molecule consisting ofthiophene end-groups and DPP (M2) were synthesized. Then we investigated theoptical, electrochemical, thermal and photovoltaic properties of these molecules.These materials possess strong absorption at475-750nm and low-lying HOMO levels(5.28eV~5.35eV). SMBHJ solar cells based on M1-M3/PC71BM blends (1:1,w/w) demonstrate power conversion efficiencies (PCEs) as high as2.59%, andnaphthalene-ended M1and M3show higher photovoltaic performance than M2dueto broad absorption and better morphology of the devices.2. We synthesized two new D-A-D type organic small molecules, one consistingof thiophene end-groups and π-extended isoindigo unit (LY1) and the other moleculeconsisting of TPA end-groups and π-extended isoindigo unit (LY2), bypalladium-catalyzed cross-coupling reaction (as shown in Scheme1). And a polymer(P1) which consist of benzo[1,2-b:4,5-b’]dithiophene (BDT) and π-extendedisoindigo unit had been synthesized, we had investigated part of its properties due its poor solubility. So we just studied the optical, electrochemical, thermal andphotovoltaic properties of small molecules LY1and LY2. Compounds LY1and LY2exhibited low-lying HOMO levels (5.29eV and5.59eV) and extremely low-lyingLUMO levels (4.05eV and4.06eV) due to the extremely strong electron-decientπ-extended isoindigo unit, and can be used as donors or acceptors in SMBHJ solarcells.