Ultrathin solution-processed single crystals of thiophene-phenylene co-oligomers for organic field-effect devices

Thiophene-phenylene co-oligomers (TPCO) single crystals are promising materials for organic light-emitting devices, e.g., light-emitting transistors (OLETs), due to their ability to combine high luminescence and efficient charge transport. However, optical confinement in platy single crystals strongly decreases light emission from their top surface degrading the device performance. To avoid optical waveguiding, single crystals thinner than 100 nm would be beneficial. Herein, we report on solution-processed ultrathin single crystals of TPCO and study their charge transport properties. As materials we used 1,4-bis(5'-hexyl-2,2'-bithiophene-5-yl)benzene (DH-TTPTT) and 1,4-bis(5'-decyl-2,2'-bithiophene-5-yl)benzene (DD-TTPTT). The ultrathin single crystals were studied by optical polarization, atomic-force, and transmission electron microscopies, and as active layers in organic field effect transistors (OFET). The OFET hole mobility was increased tenfold for the oligomer with longer alkyl substituents (DD-TTPTT) reaching 0.2 cm2/Vs. Our studies of crystal growth indicate that if the substrate is wetted, it has no significant effect on the crystal growth. We conclude that solution-processed ultrathin TPCO single crystals are a promising platform for organic optoelectronic field-effect devices.

[1]  Zhenan Bao,et al.  Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains. , 2013, Nature materials.

[2]  S. Hotta,et al.  The thiophene/phenylene co-oligomers: exotic molecular semiconductors integrating high-performance electronic and optical functionalities , 2011 .

[3]  V. Bruevich,et al.  Molecularly Smooth Single-Crystalline Films of Thiophene–Phenylene Co-Oligomers Grown at the Gas–Liquid Interface , 2014 .

[4]  L. Torsi,et al.  Organic Transistors: Two-Dimensional Transport and Improved Electrical Characteristics , 1995, Science.

[5]  S. Hotta,et al.  Single-Crystal Growth and Charge Transport Properties of an Alternating Co-Oligomer Composed of Thiophene and Phenylene Rings , 2010 .

[6]  H. Klauk,et al.  1,4-bis(5-decyl-2,2′-bithien-5-yl)benzene as new stable organic semiconductor for high performance thin film transistors , 2005 .

[7]  K. Raghavachari,et al.  Thiophene-Phenylene and Thiophene-Thiazole Oligomeric Semiconductors with High Field-Effect Transistor On/Off Ratios , 2001 .

[8]  Fabio Biscarini,et al.  Spatially correlated charge transport in organic thin film transistors. , 2004, Physical review letters.

[9]  Jun Wang,et al.  Novel thiophene-aryl co-oligomers for organic thin film transistors , 2005 .

[10]  V. G. Konstantinov,et al.  Highly bendable luminescent semiconducting organic single crystal , 2017 .

[11]  S. Hotta.  Organic single-crystal light-emitting field-effect transistors , 2014, 2015 20th Microoptics Conference (MOC).

[12]  S. Hotta,et al.  Direct formation of thin single crystals of organic semiconductors onto a substrate , 2007 .