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Yonggang Zhen1 Ping He1 Zongpeng Zhang1 Deyang Ji1 Eiichi Nakamura2 Wenping Hu1 3

1, Institute of Chemistry, CAS, Beijing, , China
2, The University of Tokyo, Tokyo, , Japan
3, Tianjin University, Tianjin, , China

Tailoring crystal polymorph and co-assembly into bicomponent or multicomponent solids are two important strategies of crystal engineering to improve the optoelectronic properties of organic semiconductors, which is highly challenging due to the weak nondirectional intermolecular interactions in organic solids.
Herein, we report the controllable growth of different crystal phases of organic semiconductors, i.e. pentacene1, thienoacene (BDTDT)2 and phthalocyanine derivatives (TiOPc)3 through polymorph induction of surface nanogrooves, solution supersaturation or vapor transport temperature gradient. The surface nanogrooves is highly important to induce the growth of orthorhombic phase pentacene films with extremely high mobility up to 30.6 cm2 V-1 s-1. The big discrepancies of charge transport in two different crystal polymorphs for BDTDT (8.5 vs. 18.9 cm2 V-1 s-1) and TiOPc (0.1 vs. 26.8 cm2 V-1 s-1) were observed clearly. In the case of BDTDT, we recognized the importance of electronic couplings of (HOMO-1) to charge transport behaviour, which is generally ignored to account for the carrier mobility. In the case of TiOPc, we demonstrated experimentally that inter-layer electronic couplings may result in a drastic decrease of charge mobilities utilizing field-effect transistors if the coupling direction perpendicular to the current direction.
Furthermore, a solid solution of two porphyrin derivatives was achieved by in-situ heating their soluble precusors mixture.4 Organic solar cells based on the solid solution was demonstrated for the first time, resulting in a power conversion efficiency value much higher than the devices using the single component. Last but not the least, we demonstrate the photocurrent generation of molecular heterojunction co-crystals. Theoretical calculations reveals the different charge recombination degree of these two co-crystals, indicating that molecualr stacking plays an important role in the photovoltaic effects. This work opens an avenue to develop molecular scale p-n junction cocrystals as a promising donor-acceptor contacting mode for application in organic solar cells.5
1. Ji, D.; Xu, X.; Jiang, L.; Amirjalayer, S.; Jiang, L.; Zhen, Y.*; Zou, Y.; Yao, Y.; Dong, H.; Yu, J.; Fuchs, H.; Hu, W., J. Am. Chem. Soc. 2017, 139, 2734.
2. He, P.; Tu, Z.; Zhao, G.; Zhen, Y.*; Geng, H.; Yi, Y.*; Wang, Z.; Zhang, H.; Xu, C.; Liu, J.; Lu, X.; Fu, X.; Zhao, Q.; Zhang, X.; Ji, D.; Jiang, L.; Dong, H.; Hu, W.*, Adv. Mater. 2015, 27, 825.
3. Zhang, Z.; Jiang, L.; Cheng, C.; Zhen, Y.*; Zhao, G.; Geng, H.; Yi, Y.*; Li, L.; Dong, H.; Shuai, Z.; Hu, W.*, Angew. Chem. Int. Ed. 2016, 55, 5206.
4. Zhen, Y.; Tanaka, H.*; Harano, K.; Okada, S.; Matsuo, Y.*; Nakamura, E.*, J. Am. Chem. Soc. 2015, 137, 2247.
5. Zhang, H.; Jiang, L.; Zhen, Y.*; Zhang, J.; Han, G.; Zhang, X.; Fu, X.; Yi, Y.*; Xu, W.*; Dong, H.; Chen, W.; Hu, W.*; Zhu, D., Adv. Electron. Mater. 2016, 2, 1500423.

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