Molecular design through computational simulation on the benzo[2,1-b;3,4-b′]dithiophene-based highly ordered donor material for efficient polymer solar cells

Abstract

Donor–acceptor (D–A) copolymers have been proved to be excellent candidates for efficient polymer solar cells (PSCs). An easy and powerful strategy of D–A copolymer design to enhance the performance of PSCs would advance their industrialization. Here we demonstrate an effective molecular design method using the simple molecular mechanics function of MM2 (Molecular Mechanic program 2) & MMFF94 (Merck Molecular Force Field 94) calculation and noncovalent conformational locking effects in the D–A polymer backbone. It is shown to play an important role in D–A copolymers with a highly ordered structure through intra- and/or intermolecular interactions. We report a newly designed D–A copolymer donor, poly(benzodithiophene-dibenzophenazine), P(BDP-DTPz), using our strategy which exhibits good solubility, high molecular ordering and excellent charge carrier mobility balance. A maximum power conversion efficiency (PCE) of 6.2% is achieved with a P(BDP-DTPz):PC₇₁BM blend under 1.5 G solar irradiation. This work will provide a new perspective for molecular design of D–A copolymers in PSCs.