Synthesis and Characterization of Dialkylthio Side Chains Modified Benzo[1,2‐b:4,5‐b’]dithiophene‐Based Conjugated Polymer for Organic Solar Cells

Abstract

AbstractIn this paper, two conjugated polymers named PBDT‐OT‐BT and PBDT‐DST‐BT, derived from 4,8‐bis(4,5‐dioctylthiophen‐2‐yl)benzo[1,2‐b : 4,5‐b’]dithiophene (BDT‐OT) or 4,8‐bis(4,5‐bis(octylthio)thiophene‐2‐yl)benzo[1,2‐b : 4,5‐b’]dithiophene (BDT‐DST) as the electron‐donating unit and benzo[c][1,2,5]thiadiazole (BT) as electron‐withdrawing unit were synthesized and characterized. It was found that compared to the alkyl side chain substituted polymer PBDT‐OT‐BT, the two alkylthio side chain modified polymer PBDT‐DST‐BT exhibited lower highest occupied molecular orbital (HOMO) energy level, weaker crystallinity characteristic, and higher dielectric constant (ϵr) at 1 kHz. However, PBDT‐DST‐BT also presented relatively poor miscibility with Y6 in comparison with PBDT‐OT‐BT, which had a negative effect on the bulk heterojunction morphology and hindered the exciton dissociation and carrier collection. Eventually, the PBDT‐DST‐BT : Y6 based polymer solar cells (PSCs) achieved a power conversion efficiency (PCE) of 2.27 % much lower than that of the PBDT‐OT‐BT : Y6 based device (PCE=9.46 %). These results would provide a deep understanding of the influence of alkylthio side groups on the properties of polymer donors in PSCs.