An Indacenodithiophene-Quinoxaline Polymer Prepared by Direct Arylation Polymerization for Organic Photovoltaics

Seeking preparation of high-performance donor-acceptor (D-A) polymers based on bare thiophene units in a more environmentally friendly and faster way, we have carried out a direct arylation polymerization (DAP) of two starting beta-unprotected thiophene-containing monomers (indacenodithiophene (IDT) and thiophene-quinoxaline-thiophene (TQ)). Through modulating DAP time and heating method, the resulting IDT-TQpolymer shows a relatively well-defined structure with low content of structural defects, as demonstrated by high temperature H-1 NMR, MALDI-TOF-MS, and elemental analysis. Integrating this polymer into bulk-heterojunction solar cells with PC71BM can induce an enhanced OPV performance compared to the other structural analogues that retain a certain amount of unwanted structural defects. However, the film morphology and crystallinity are negligibly influenced by the degree of the structural defects. Through a combination of detailed electrical measurements using light intensity dependence and net photocurrent, we are able to correlate the different photovoltaic performances in structure-function relationships with the extent of the structural defects. Our study indicates that DAP is a promising asset for environmental production of many valuable thiophene-containing polymers for electroactive and photoactive applications.