Journal
JOURNAL OF PHOTONICS FOR ENERGY
Volume 5, Issue -, Pages -Publisher
SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS
DOI: 10.1117/1.JPE.5.057213
Keywords
donor-acceptor oligomer; charge generation; dicyanovinyl group; thienothiadiazole; benzothiadiazole; organic solar cell; charge carrier mobility
Funding
- Program of President of Russian Federation for Support of Young Scientists [MK-5061.2015.3]
- Russian Foundation for Basic Research Synthetic Carbon Allotropes [13-03-12451, Sonderforschungsbereich 953]
- Solar Technologies go Hybrid (SolTech)
- Program of Presidium of Russian Academy of Sciences [P8]
- China Scholarship Council (CSC)
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Two pi-conjugated acceptor-donor-acceptor-donor-acceptor-type (A-D-A-D-A) oligothiophenes, TT-(2T-DCV-Hex)(2) and BT-(2T-DCV-Hex)(2) were designed and synthesized with thienothiadiazole (TT) or benzothiadiazole (BT) as the core and dicyanovinyl (DCV) as the terminal acceptor groups for comprehensively investigating and understanding structure-property relationships. The resulting oligomers were first characterized by thermal analysis, UV-Vis spectroscopy, and cyclic voltammetry. By simply changing the BT to TT core in these two oligothiophenes, the highest occupied molecular orbital levels were varied from -5.55 eV for BT-(2T-DCV-Hex)(2) to -5.11 eV for TT-(2T-DCV-Hex)(2), and the optical band gaps were varied from 1.72 eV for BT-(2T-DCV-Hex)(2) to 1.25 eV for TT-(2T-DCV-Hex)(2), ascribed to the stronger electron accepting character of the TT core. However, the power conversion efficiency of bulk heterojunction organic solar cells (OSCs) with TT-(2T-DCV-Hex)(2) as donor and [6,6]-phenyl C-70 -butyric acid methyl ester (PC71BM) as acceptor was measured to be 0.04% only, which is much lower than that of BT-(2T-DCV-Hex)(2) : PC71BM (1.54%). Compared to the TT-(2T-DCV-Hex)(2) system, the BT-(2T-DCV-Hex)(2) based device shows smoother film surface morphology, and superior charge generation and charge carrier mobilities. Therefore, the results clearly demonstrate that in addition to modifying the alkyl side chains and pi-bridge lengths, the design of new small molecules for high-performance OSCs should also aim to choose suitable acceptor units. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
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