p-Channel Organic Semiconductors Based on Hybrid Acene−Thiophene Molecules for Thin-Film Transistor Applications

Abstract

We report the structural and electrical characterization of two new p-channel organic semiconductors, 5,5'-bis(2-tetracenyl)-2,2'-bithiophene (1) and 5,5'-bis(2-anthracenyl)-2,2'-bithiophene (2). Both compounds exhibited a high degree of thermal stability with decomposition temperatures of 530 degrees C and 425 degrees C for 1 and 2, respectively. The thin-film structures of 1 and 2 were examined using wide-angle X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXD), and atomic force microscopy (AFM). Films of 1 and 2 pack in similar triclinic unit cells with the long axes of the molecules nearly perpendicular to the substrate. Thin-film transistors (TFTs) based on 1 and 2 exhibit contact-corrected linear regime hole mobility as high as 0.5 cm2/Vs and 0.1 cm2/Vs, respectively. The specific contact resistance at high gate voltages for gold top contacts was 2 x 10(4) Ohms cm and 3 x 10(4) Ohms cm for 35 nm thick films of 1 and 2, respectively. Long-term air stability tests revealed less degradation of the electrical properties of 1 and 2 in comparison to pentacene. Variable temperature measurements revealed activation energies as low as 22 and 27 meV for 1 and 2, respectively. The temperature and gate voltage dependence of the mobility are discussed in terms of a double exponential distribution of trap states and a model accounting for the layered structure of the organic films. The enhanced air and thermal stability over pentacene, combined with good electrical performance characteristics, make 2 a promising candidate for future organic TFT applications.

Chain Length Effect of Dialkoxynaphthalene End-Capped Divinylbenzene for OTFT

“…28 Recently, several groups have reported significant enhancements of the stability of OTFTs under ambient conditions with semiconducting small molecules, [29][30][31][32][33] oligomers, 22,24,[34][35][36][37][38][39] and polymers. Recently, our group reported anthracene main core with dialkoxynaphthalene end-capper had good oxidation stability and exhibited a field-effect performance with a mobility of 0.64 cm 2 /V·s, a subthreshold slope of 0.8 V and an on/off ratio of 7.5 × 10…”

“…A large number of oligomers have demonstrated interesting performances in OTFTs, such as fluorene, acenes and carbazole derivatives. [18][19][20][21] The synthesis of new π-conjugated units that could be incorporated in oligomeric structures could be desirable for significant optimization of OTFT performances and for a better understanding of the structure-property relationship.…”

Hole-vibronic coupling in oligothiophenes: impact of backbone torsional flexibility on relaxation energies

“…Recently, a hybrid thiophene-acene semiconductor has been investigated and revealed high mobility and increased air stability, indicating that the properties of the two fragments (acene and thiophene) can be combined to design a material with overall superior performance (Kwon et al 2004;Heeney et al 2005;Merlo et al 2005;Coropceanu et al 2006).…”

Progresses in organic field-effect transistors and molecular electronics

“…Li et. al [16] reported OFETs based on indolo[3,2-b]carbazoles with mobility of 0.2 cm 2 /V s, Merlo et.al [17] found the mobility of hybrid acene-thiophene molecules was as high as 0.5 cm 2 /V s, Naraso et. al [18] fabricated OFETs based on DN-TTF derivatives with mobility of 0.42 cm 2 /V s. As for n type materials, Haddon et.al [19] fabricated…”