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Difluorobenzothiadiazole‐Based Small‐Molecule Organic Solar Cells with 8.7% Efficiency by Tuning of π‐Conjugated Spacers and Solvent Vapor Annealing
Author(s) -
Wang JinLiang,
Xiao Fei,
Yan Jun,
Wu Zhuo,
Liu KaiKai,
Chang ZhengFeng,
Zhang RuBo,
Chen Hui,
Wu HongBin,
Cao Yong
Publication year - 2016
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.201505020
Subject(s) - materials science , thiophene , annealing (glass) , conjugated system , organic solar cell , band gap , photoactive layer , molecule , polymer solar cell , solvent , chemical engineering , solar cell , polymer , nanotechnology , optoelectronics , organic chemistry , chemistry , composite material , engineering
The synthesis of a series of tetrafluorine‐substituted, wide‐bandgap, small molecules consisting of various π‐conjugated spacers (furan, thiophene, selenophene) between indacenodithiophene as the electron‐donating core and the electron‐deficient difluorobenzothiadiazole unit is reported and the effect of the π‐conjugated spacers on the photovoltaic properties is investigated. The alteration of the π‐conjugated spacer enables fine‐tuning of the photophysical properties and energy levels of the small molecules, and allows the adjustment of the charge‐transport properties, the morphology of the photoactive films, as well as their photovoltaic properties. Moreover, most of these devices exhibit superior device performances after CH 2 Cl 2 solvent annealing than without annealing, with a high fill factor (0.70–0.75 for all cases). Notably, the devices based on the new molecule BIT4FTh (with thiophene as the spacer) show an outstanding PCE of 8.7% (with an impressive FF of 0.75), considering its wide‐bandgap (1.81 eV), which is among the highest efficiencies reported so far for small‐molecules‐based solar cells. The morphologies of the photoactive layers with/without CH 2 Cl 2 solvent annealing are characterized by atomic force microscopy, transmission electron microscopy and two‐dimensional grazing incidence X‐ray diffraction analysis. The results reported here clearly indicate that highly efficient small‐molecules‐based solar cells can be achieved through rational design of their molecular structure and optimization of the phase‐separated morphology via an adapted solvent–vapor annealing process.