Premium
Benzobisthiazole as Weak Donor for Improved Photovoltaic Performance: Microwave Conductivity Technique Assisted Molecular Engineering
Author(s) -
Tsuji Masashi,
Saeki Akinori,
Koizumi Yoshiko,
Matsuyama Naoto,
Vijayakumar Chakkooth,
Seki Shu
Publication year - 2014
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201301371
Subject(s) - materials science , polymer solar cell , copolymer , polymer , miscibility , band gap , conjugated system , acceptor , homo/lumo , organic solar cell , density functional theory , fullerene , photovoltaics , photovoltaic system , optoelectronics , energy conversion efficiency , chemical engineering , molecule , organic chemistry , computational chemistry , composite material , ecology , physics , engineering , biology , condensed matter physics , chemistry
New donor–acceptor‐type copolymers comprised of benzobisthiazole (BBTz) as a weak donor rather than acceptor are proposed. This approach can simultaneously lead to deepening the HOMO and LUMO of the polymers with moderate energy offset against fullerene derivatives in bulk heterojunction organic photovoltaics. As a proof‐of‐concept, BBTz‐based random copolymers conjugated with typical electron acceptors: thienopyrroledione (TPD) and benzothiadiazole (BT) based on density functional theory calculations are synthesized. Laser‐flash and Xe‐flash time‐resolved microwave conductivity (TRMC) evaluations of polymer:[6,6]‐phenyl C 61 butyric acid methyl ester (PCBM) blends are conducted to screen the feasibility of the copolymers, leading to optimization of processing conditions for photovoltaic device application. According to the TMRC results, alternating BBTz‐BT copolymers are designed, exhibiting extended photoabsorption up to ca. 750 nm, deep HOMO (–5.5 to –5.7 eV), good miscibility with PCBM, and inherent crystalline nature. Moreover, the maximized PCE of 3.8%, the top‐class among BBTz‐based polymers reported so far, is realized in an inverted cell using TiO x and MoO x as the buffer layers. This study opens up opportunities to create low‐bandgap polymers with deep HOMO, and shows how the device‐less TRMC evaluation is of help for decision‐making on judicious molecular design.