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Side Chain Engineering on Medium Bandgap Copolymers to Suppress Triplet Formation for High‐Efficiency Polymer Solar Cells
Author(s) -
Xue Lingwei,
Yang Yankang,
Xu Jianqiu,
Zhang Chunfeng,
Bin Haijun,
Zhang ZhiGuo,
Qiu Beibei,
Li Xiaojun,
Sun Chenkai,
Gao Liang,
Yao Jia,
Chen Xiaofeng,
Yang Yunxu,
Xiao Min,
Li Yongfang
Publication year - 2017
Publication title -
advanced materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.707
H-Index - 527
eISSN - 1521-4095
pISSN - 0935-9648
DOI - 10.1002/adma.201703344
Subject(s) - materials science , side chain , thiophene , polymer solar cell , conjugated system , acceptor , polymer , photochemistry , energy conversion efficiency , alkyl , band gap , copolymer , annealing (glass) , absorption spectroscopy , homo/lumo , polymer chemistry , chemical engineering , optoelectronics , organic chemistry , chemistry , molecule , optics , engineering , physics , composite material , condensed matter physics
Suppression of carrier recombination is critically important in realizing high‐efficiency polymer solar cells. Herein, it is demonstrated difluoro‐substitution of thiophene conjugated side chain on donor polymer can suppress triplet formation for reducing carrier recombination. A new medium bandgap 2D‐conjugated D–A copolymer J91 is designed and synthesized with bi(alkyl‐difluorothienyl)‐benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit, for taking the advantages of the synergistic fluorination on the backbone and thiophene side chain. J91 demonstrates enhanced absorption, low‐lying highest occupied molecular orbital energy level, and higher hole mobility, in comparison with its control polymer J52 without fluorination on the thiophene side chains. The transient absorption spectra indicate that J91 can suppress the triplet formation in its blend film with n‐type organic semiconductor acceptor m ‐ITIC (3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene). With these favorable properties, a higher power conversion efficiency of 11.63% with high V OC of 0.984 V and high J SC of 18.03 mA cm −2 is obtained for the polymer solar cells based on J91 / m ‐ITIC with thermal annealing. The improved photovoltaic performance by thermal annealing is explained from the morphology change upon thermal annealing as revealed by photoinduced force microscopy. The results indicate that side chain engineering can provide a new solution to suppress carrier recombination toward high efficiency, thus deserves further attention.