Synthesis And Photovoltaic Properties Of Novel Conjugated Polymers Based On Benzodithiophene

In recent years polymer solar cells (PSCs) have received increasing attention inboth academia and industry. Nowadays, the design, synthesis and tunabilty ofoptoelectronic properties of polymer donor materials are the main focuses in this field.Consequently, in this report we design and synthesis seires of new donor-acceptor(D-A) conjugated polymers based on benzodithiophene (BDT) with the aim toachieve high performamce polymer donor materials in PSCs. The optical,electrochemical, and photovoltaic properties of these D-A copolymers wereinvestigated in detail. The main research contents of this dissertation are as follows:1. Two D-A copolymers, PEHBDT-BTz and PODBDT-BTz, containing thesame backbone of BDT and bithiazole (BTz) units but different side chains weredesigned and synthesized. Effects of the side chains of BDT and BTz units onsolubility, absorption spectra, energy levels, film morphology, and photovoltaicproperties of the polymers were investigated. Results showed that the more branchedside chains could increase the molecular weight and the introduction of alkylthienylgroups into BTz unit benefits to broaden the absorption and lower the bandgaps aswell as deepen HOMO levels. PCE of PSCs based on the copolymers varied from2.92%for PODBDT-BTz to3.71%for PEHBDT-BTz, depending on the type andtopology of the side chains on the BDT moiety.2. A series of donor-π-acceptor (D-π-A) conjugated copolymers (PBDT-AT,PDTS-AT, PBDT-TT, and PDTS-TT), based onbenzo[1,2-b:4,5-c′]dithiophene-4,8-dione acceptor unit with benzodithiophene ordithienosilole as donor unit, alkylthiophene or thieno[3,2-b]thiophene as conjugatedπ-bridge, were designed and synthesized for application as donor materials in PSCs.Effects of the donor unit and π-bridge on the optical and electrochemical properties,hole mobilities and photovoltaic performance of the D-π-A copolymers wereinvestigated. The results showed that polymers with BDT as the donor unit havebroader and red-shifted absorption spectra that those of DTS containg polymers.Moreover, the different π-bridges have more significant effect on the HOMO energylevels than that of the different in these D-π-A copolymers. PSCs based on PBDT-ATgave the best photovoltaic performance with a PCE as high as5.91%.