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

• Published in: Advanced functional materials Vol. 27; no. 38
• Main Authors: Kim, Sang Woo, Choi, Joonhyeong, Bui, Thi Thu Trang, Lee, Changyeon, Cho, Changsoon, Na, Kwangmin, Jung, Jihye, Song, Chang Eun, Ma, Biwu, Lee, Jung‐Yong, Shin, Won Suk, Kim, Bumjoon J.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 12-10-2017
• Subjects: all‐polymer solar cells; complementary light absorption; donor–acceptor random copolymers; Electromagnetic absorption; Energy conversion efficiency; Fluorination; Light; Materials science; Photovoltaic cells; polymer acceptors; Polymers; Properties (attributes); Solar cells; tunable energy levels
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201703070

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).
A series of poly(benzodithiophene‐r‐fluorinated‐thienothiophene) [P(BDTT‐r‐TT‐F)] random copolymers with tunable light absorption characteristics are developed by controlling the ratios of electron‐rich BDTT and electron‐deficient TT‐F units. All‐polymer solar cells (all‐PSCs) fabricated from these polymer donors and the P(NDI2HD‐T2) acceptor achieve efficiencies of up to 6.8% by optimizing the complementary light absorption of the polymer donor and acceptor.