Synthesis And Photovoltaic Properties Of D-A Copolymers Based On Thiazole Or Benzotriazole And Triphenylamine-Based Small Molecule

In this dissertation, major work is focusing on the design and synthesis of new conjugated polymer donor materials and organic small molecule donor materials for the application in organic solar cells. The main results are as follows:(1) Two new D-A conjugated polymers containing benzodithiophene donor unit and the acceptor unit of bithiazole (BTz) or thiazolothiazole (TzTz), P1and P2, were synthesized by Stille cross-coupling polymerization. The thermal, optical and electrochemical properties were well investigated. Bulk heteroj unction polymer solar cell devices based on an active layer of electron donor copolymers, P1and P2, blended with electron acceptor [6,6]-phenyl-C71butyric acid methyl ester (PC71BM) in the weight ratio of1:2were explored, the external quantum efficiency (EQE) measurements showed a peak external quantum efficiency of45%for P1and P2. The first result of PSC device with P2and PC71BM in the weight ratio of1:2gave an overall power conversion efficiency (PCE) of2.6%, an open-circuit voltage (Voc) of0.77V, a short-circuit current (Jsc) of6.68mA/cm2, and a fill factor (FF) of0.51, under the illumination of AM1.5,100mW/cm2.(2) Three D-A copolymers containing benzotriazole (BTz) acceptor unit and different donor units of benzodithiophene (BDT), dithienopyrrole (DTP), and carbazole, PBDT-DTBTz, PDTP-DTBTz, and PC-DTBTz, were synthesized for the application as donor materials in polymer solar cells (PSCs). By changing the donor units, the band gaps and HOMO (the highest occupied molecular orbital) energy levels of the copolymers could be finely tuned. PC-DTBTz exhibited the lowest HOMO energy level of-5.34eV, and the lowest HOMO energy level translates into a highest Voc of0.73V in PC-DTBTz-based BHJ devices.The PCE of the PSCs based on these copolymers and [6,6]-phenyl-C61butyric acid methyl ester (PC61BM) were1.55%(PBDT-DTBTz),0.34%(PDTP-DTBTz), and1.33%(PC-DTBTz), respectively, under the illumination of AM1.5,100mW/cm2. (3) A new linear, D-A-D organic small molecule (Ml) with TPA as donor (D) unit, isoindigo as accept (A) unit was synthesized by Stille coupling reactions. It exhibits broad and strong absorption (300-700nm), and a relatively low HOMO energy level (-5.30eV) and band gap (1.69eV), relatively high hole mobility (2.49×10-4cm2/Vs). Solution-processed small-molecule bulk-heterojunction (BHJ) solar cells based on Ml:PC61BM(1:3,w/w) blend film exhibits a power conversion efficiency (PCE) of0.84%with an open-circuit voltage (Voc) of0.78V under the illumination of AM1.5,100mW/cm2.