Benzodithiophene-based polymers containing novel electron accepting selenophene-incorporated pyrrolo[3,4-c]pyrrole-1,3-dione units for highly efficient thin film transistors and polymer solar cells

A new electron deficient monomer, 4,6-bis(5-bromoselenophen-2-yl)-2,5-dioctylpyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (SDPPDS), was prepared and co-polymerized with an electron rich distannyl derivative of 4,8-bis(2-ethylhexyloxy) benzo[1,2-b:4,5-b′]dithiophene (BDT) and 4,8-bis(5-(2-ethylhexyl) thiophen-2-yl) benzo[1,2-b:4,5-b′]dithiophene (BDTT) to afford polymers P(BDT-SDPPDS) and P(BDTT-SDPPDS), respectively. The optical band gaps of P(BDT-SDPPDS) and P(BDTT-SDPPDS) were estimated to be 2.03 eV and 1.97 eV, respectively. The estimated HOMO/LUMO energy levels of P(BDT-SDPPDS) and P(BDTT-SDPPDS) were –5.43 eV/–3.43 eV and–5.49 eV/–3.53 eV, respectively. The organic thin film transistor made from the polymers P(BDT-SDPPDS) and P(BDTT-SDPPDS) displayed an impressive hole mobility of 2 × 10−4 cm2/Vs and 1.2 × 10−3 cm2/Vs, respectively. The polymer solar cells (PSC) made with a device structure of ITO/PEDOT:PSS/P(BDT-SDPPDS) or P(BDTT-SDPPDS):PC70BM + 3 vol% DIO/Ca/Al showed a solar to electrical energy conversion efficiency of 2.26% and 4.45%, respectively.