New alkylselenyl substituted benzodithiophene-based solution-processable 2D π-conjugated polymers for bulk heterojunction polymer solar cell applications

Abstract

We have introduced 2-ethylhexylselenophene as a side chain substituent on benzodithiophene (BDT) unit, where the selenophene ring is attached to 4th and 8th positions of the phenyl ring in BDT to obtain BDTSe as an electron rich moiety. A new bisbenzothiadazole (BBT) derivative was also synthesized namely, 3,3'-diheptyl-3,4-propylenedioxythienyl-BBT, in which 3,3'-diheptyl-3,4-propylenedioxythienyl group is inserted between two BT groups. 3,3'-Diheptyl-3,4-propylenedioxythienyl-BBT and 1,3-dibromo-5-(2-ethylhexyl)-5H-thieno[3,4-c]pyrrole-4,6-dione (TPD) were used as acceptor segments for the synthesis of donor–acceptor (D–A) polymers, represented by P1 and P2, respectively. Thin film transistors were fabricated using the thin films of P1 and P2 and the field effect hole mobilities are 2.7×10–3 and 4.2×10–4cm2V–1s–1, respectively. A bulk heterojunction polymer solar cell (BHJ PSC) that contain P1 delivered high power conversion efficiency (PCE) value of 4.51% (with 1vol% DIO) and 4.16% (with 1vol% CN) with high short-circuit current density (Jsc) of 11.7 and 10.96mA/cm2, respectively.