Rationally Designed Donor-Acceptor Random Copolymers with Optimized Complementary Light Absorption for Highly Efficient All-Polymer Solar Cells

Abstract

Most of the high-performance all-polymer solar cells (all-PSCs) reported to date are based on polymer donor and polymer acceptor pairs with largely overlapped light absorption properties, which seriously limits the efficiency of all-PSCs. This study reports the development of a series of random copolymer donors possessing complementary light absorption with the naphthalenediimide- based polymer acceptor P(NDI2HD-T2) for highly efficient all-PSCs. By controlling the molar ratio of the electron-rich benzodithiophene (BDTT) and electron-deficient fluorinated-thienothiophene (TT-F) units, a series of polymer donors with BDTT: TT-F ratios of 1: 1 (P1), 3: 1 (P2), 5: 1 (P3), and 7: 1 (P4) are prepared. The synthetic control of polymer composition allows for precise tuning of the light absorption properties of these new polymer donors, enabling optimization of light absorption properties to complement those of the P(NDI2HD-T2) acceptor. Copolymer P1 is found to be the optimal polymer donor for the fullerene-based solar cells due to its high light absorption, whereas the highest power conversion efficiency of 6.81% is achieved for the all-PSCs with P3, which has the most complementary light absorption with P(NDI2HD-T2).