Effect of Acceptor Lamination on Photocarrier Dynamics in Hole Transporting Hexabenzocoronene Nanotubular Self-Assembly

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• 作者：Yusuke Wakikawa ; Tadaaki Ikoma ; Yohei Yamamoto ; Takanori Fukushima ; Takuzo Aida ; Kimio Akiyama
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：July 25, 2013
• 年：2013
• 卷：117
• 期：29
• 页码：15295-15305
• 全文大小：586K
• 年卷期：v.117,no.29(July 25, 2013)
• ISSN：1932-7455

文摘

Measurements of transient photoconductance under an external magnetic field were used to investigate photocarrier dynamics in low-dimensional hexabenzocoronene (HBC) self-assemblies, which are a promising material group for highly efficient solar cells achieved by bottom-up technology, and to clarify the effect of lamination with electron acceptor layer on the surfaces of HBC nanotubes. In an HBC column without an acceptor, the carrier generation yield from a geminate electron鈥揾ole (e-h) pair is dependent on the external electric and magnetic fields. The time dependence of the magnetic field effect on geminate e-h pair dynamics in the HBC column structure was analyzed to estimate the recombination rate constants of the singlet and triplet e-h pairs (k_r^S and k_r^T), which were 1.5 脳 10⁸ and 1.2 脳 10⁸ s^鈥? respectively. The same kinetic analysis with consideration of the electric field effect on the photocarrier generation yield provided an electric field dependent dissociation rate constant in the range of 10⁷鈥?0⁸ s^鈥? in the HBC column structure. However, neither electric nor magnetic field effects on the carrier generation process were observed in acceptor-appended HBC nanotubes. The disappearance of the external field effects in acceptor-appended HBC indicates that the geminate recombination is reduced substantially by a well-organized donor/acceptor heterojunction with an interval of a few nanometers due to some 蟽-bonds. However, efficient nongeminate recombination with a ratio of k_r^S:k_r^T = 1.0:0.8 in the acceptor-appended HBC nanotubes was also elucidated by the incident photon density and magnetic field effects, which is an inherent nature in materials with high carrier density.