title: Function of CN group in organic sensitizers: The first principle study.
abstract: The cyano group (CN) of the acceptor in organic sensitizers plays an important role for highly efficient dye-sensitized solar cells. In this paper, three 5, 6-difluoro-2,1,3-benzothiadiazole (DFBTD) organic molecules with different number of CN units, named ME15, ME16 and ME17, were investigated by the density functional theory (DFT) and time-dependent DFT (TDDFT). We analyzed the CNs effects on the electronic structures, optical properties, adsorption modes and electron transfer and injection. The result shows that ME17 has the largest maximum absorption wavelength (λmax) among these new designed dyes due to the strong electron withdrawing ability of two CNs. In addition, CN greatly influence the adsorption modes of dye/TiO2and electron injection mechanism. ME16 with one CN also has good optical absorption properties and its acceptor has the strongest coupling strength with the TiO2semiconductor which is favorable for electron transfer and injection. Thus, we believe that the number of CN groups in acceptor should be moderate and one CN in D-A-π-A structure dyes may be the more appropriate focusing on the light harvesting ability, electron transfer and electron injection.
authors.affiliation: State Key Laboratory of Heavy Oil Processing, Beijing Key Laboratory of Optical Detection Technology for Oil and Gas, and College of Science, China University of Petroleum, Beijing 102249, PR China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Heavy Oil Processing, Beijing Key Laboratory of Optical Detection Technology for Oil and Gas, and College of Science, China University of Petroleum, Beijing 102249, PR China.
authors.forename: Di
authors.initials: D
authors.lastname: Shao
authors.affiliation: State Key Laboratory of Heavy Oil Processing, Beijing Key Laboratory of Optical Detection Technology for Oil and Gas, and College of Science, China University of Petroleum, Beijing 102249, PR China.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Bai
authors.affiliation: State Key Laboratory of Heavy Oil Processing, Beijing Key Laboratory of Optical Detection Technology for Oil and Gas, and College of Science, China University of Petroleum, Beijing 102249, PR China; Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB30HE, United Kingdom. Electronic address: yangzhenqing@yahoo.com.
authors.forename: Zhenqing
authors.initials: Z
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Heavy Oil Processing, Beijing Key Laboratory of Optical Detection Technology for Oil and Gas, and College of Science, China University of Petroleum, Beijing 102249, PR China. Electronic address: linchundan@126.com.
authors.forename: Chundan
authors.initials: C
authors.lastname: Lin
authors.affiliation: State Key Laboratory of Heavy Oil Processing, Beijing Key Laboratory of Optical Detection Technology for Oil and Gas, and College of Science, China University of Petroleum, Beijing 102249, PR China. Electronic address: physics@cup.edu.cn.
authors.forename: Changjin
authors.initials: C
authors.lastname: Shao
keywords: CN group; DFBTD organic molecules; DFT/TDDFT/; Intramolecular charge transfer