4:30 PM - *EP01.03.04
Carrier Transport and Molecular Packing Control of Organic Semiconductors Based on Liquid-Crystalline Non- Peripheral Octaalkylphthalocyanine
Masanori Ozaki1,Akihiko Fujii1
In introducing side chains into the phthalocyanine (Pc) molecule to induce liquid crystalline (LC) phases, there are two types of molecular structures, namely, a peripheral type and non-peripheral type. We have investigated the molecular packing and electronic transport characteristics of mesogenic Pc having alkyl side chains at non-peripheral sites, 1,4,8,11,15,18,22,25-octaalkylphthalocyanine (CnPc), and their families. These compounds exhibit very high long-range drift mobility up to 1.4 cm2/Vs evaluated by time of flight measurement and must be a candidate of organic semiconductor for printable electronics [1,2]. However, this fact is contrary to expectation. Namely, it can be easily predicted that the planarity of the Pc molecular plane might be reduced due to large steric hindrance between non-peripherally substituted chains and disordered molecular stacking undesirable for carrier transport is formed.
We have also demonstrated a high-efficient bulk-heterojunction (BHJ) solar cell based on C6PcH2 and their family, which shows a high power conversion efficiency of 5.3% [3-5]. For the formation of the optimally phase-separated nano-structure for efficient carrier generation and transportation, the mesogenic properties should play an important role.
Using self-organizing characteristics of LC phase, we can fabricate a large area monodomain thin film of CnPc for electronic devices. A well-aligned uniaxial single crystal growth in large area of printed thin film was obtained by means of conversion process from LC phase in a supercooled state to crystal phase.
CnPc shows a crystal polymorphism and forms two different crystal structures (α-phase or β-phase) depending on the growth condition of the crystal. The high mobility of C6Pc reported so far is evaluated in the crystal structure of the β-phase. However, according to the theoretical prediction, higher mobility is expected in the α-phase . We have demonstrated a large area single crystalline film of α-phase converted from spin-coated β-phase Pc film, which is based on the crystal polymorphism conversion triggered by the solvent vapor treatment [7,8].
This work was partly supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan (17K18882, 18H04514), and by Advanced Low Carbon Technology Research and Development Program from the Japan Science and Technology Agency (JST-ALCA)
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 Q.-D.Dao, K. Watanabe, H. Itani, L. Sosa-Vargas, A. Fujii, Y. Shimizu and M. Ozaki, Chem. Lett., 43, 1761 (2014).
 M. Yoneya, A. Miyamoto, Y. Shimizu, M. Ohmori, A. Fujii, M. Ozaki, Jpn. J. Appl. Phys., 56, 081601 (2017).
 T. Higashi, M. Ohmori, M.F. Ramananarivo, A. Fujii, and M. Ozaki, APL Mater., 3, 126107 (2015).
 Y. Anzai, T. Higashi, H. Kajii, A. Fujii, M. Ozaki, Organic Electronics, 60, 16 (2018).