Synthesis And Photovoltaic Performance Of D-A Copolymers Based On New Acceptor Unit

Wide absorption, electron energy level matching with acceptor, good solubility, easy toform nanomorphology are the prerequisite for efficient conjugated polymer donor materials.Based upon the consideration, this dissertation is focusing on the development and synthesisof new D-A copolymers based on new acceptor unit with the characteristics of facile synthesis.The main results are as follows:(1) A series of conjugated D-π-A copolymers, based on11,12-difluorodibenzo[a,c]phenazine (DFDBPz) as acceptor unit, benzodithiophene (BDT) asdonor unit, were development and synthesized. It was found that the orientation alkyl sidechain on the thiophene-bridge affected the intermolecular π-π interaction of the conjugatedpolymers. The optimum performance of the devices is obtained at1:1weight ratio ofP3:PC70BM with PCE of1.21%, which is46%higher than that of P1-based PSCs.(2) A medium band gap copolymer PIDT-FBTA based on FBTA and IDT wassynthesized and applied as donor material in PSCs. A higher Vocwas achieved, which isbenefitted from the deeper HOMO of PIDT-FBTA. The device based onPIDT-FBTA:PC70BM with1:3weight ratio displayed enhanced PCE of3.62%. Aftermethanol treatment, a significant35%enhancement in PCE (up to4.9%) with a simultaneousimprovement in Voc(0.90V to0.92V), Jsc(7.68mA cm2to9.60mA cm2) and FF (0.52to0.55) was achieved.(3) A new D-A copolymer based on thiophene substituent on quinoxaline acceptor unitwere developed and synthesized. The device based on wk-6:PC70BM with1:2.5weight ratiodisplayed a PCE of3.15%after thermal annealing at120oC. After methanol treatment, asignificant23.8%enhancement in PCE (up to3.90%) with a simultaneous improvement inVoc(0.82V to0.83V), Jsc(10.09mA cm2to11.7mA cm2) and FF (0.38to0.40) wasachieved.(4) Two kinds of new D-A copolymers based on DTBT with an electron-withdrawinggroup on thiophene bridge were developed and synthesized. The influence of electron-withdrawing group on thermal stability, optical absorption and the electrochemicalperformance were preliminary discussed. It was found that the HOMO/LUMO energy levelsand the band gap of the copolymers could be reduced by introducing electron-withdrawinggroup on thiophene bridge of without affecting copolymer skeleton coplanar. This mayprovide a method for synthesis of narrow band gap copolymers.