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Enhanced Photovoltaic Performance of Tetrazine-Based Small Molecules with Conjugated Side Chains

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journal contribution
posted on 30.08.2017, 00:00 by Chen Wang, Chang Li, Shanpeng Wen, Pengfei Ma, Ge Wang, Changhao Wang, Huayang Li, Liang Shen, Wenbin Guo, Shengping Ruan
Two two-dimensional (2D) conjugated tetrazine-based small molecules (SMs), named TBDT­(TTzT)2 and TBDT­(TTz2T)2, were newly synthesized for photovoltaic application as donor materials. They employed a molecular backbone of D2-A-D1-A-D2 in which D1 represents an alkylthienyl substituted benzo­[1,2-b:4,5-b′]­dithiophene (BDT) unit, A represents a tetrazine (Tz) unit, and D2 is a bithiophene or terthiophene ending donor unit. These synthesized molecules showed relatively broad light harvesting range and proper energy levels with a fullerene derivative acceptor. Meanwhile, we try to explore how the molecular conjugation influences the opto-electrical properties and photovoltaic performance of the tetrazine-based SM family by making comparison with their non-2D analogues. Experimental results showed that extending main chain conjugated length broadens absorption spectra, whereas side chain conjugation extension leads to larger absorption coefficients, lower highest occupied molecular orbital energy levels, and more favorable blend morphology. The optimized 2D conjugated molecules achieved better device performance with the highest Voc of 1.03 V and FF of 65.3% after using trace amounts of additive. These results suggested that extending molecular conjugation is a feasible strategy for photovoltaic material design.