Synthesis of a novel low-bandgap polymer based on a ladder-type heptacyclic arene consisting of outer thieno[3,2-b]thiophene units for efficient photovoltaic application

A novel conjugated polymer PIDTT-quinoxaline (Qx) based on the coplanar thieno[3,2-b]thiophene-phenylene-thieno[3,2-b]thiophene structure is synthesized and evaluated as an electron-donor material for bulk-heterojunction polymer solar cells (BHJ PSCs). The absorption spectra, electrochemical, charge transport, and film morphology properties as well as theoretical modeling of PIDTT-Qx are investigated to understand its intrinsic structure-property relationship. As expected, this polymer with an extended π-conjugated backbone exhibits a narrow-bandgap and board absorption spectrum for enhanced light harvesting. BHJ PSCs (ITO/PEDOT:PSS/polymer:PC₇₁BM/interlayer/ Al) afford a maximum power conversion efficiency of 5.05% with an open-circuit voltage of 0.84 V, a short-circuit current density of 11.26 mA cm^-2, and a fill factor of 53.4%. These results demonstrate the potential of PIDTT-Qx as an efficient electron-donor material for BHJ PSCs. A novel conjugated polymer PIDTT-quinoxaline (Qx) based on the coplanar thieno[3,2-b]thiophene-phenylene- thieno[3,2-b]thiophene structure is synthesized as the electron-donor material for bulk-heterojunction polymer solar cells. The forced planarization structure with heptacyclic rings can further facilitate effective π-electron delocalization, extend effective conjugation length of the backbone, and intensely reduce the target polymer's bandgap. Efficient bulk-heterojunction polymer solar cells with PCE of about 5.1% are fabricated.