Doped interlayers enabling high-mobility p-type organic transistors with copper contact electrodes

Abstract

Thin-film single crystals of organic semiconductors (OSCs) enable simple and low-cost fabrication of high-mobility organic field-effect transistors (OFETs) via solution processing. However, injection barriers in OFETs limit material selection and device performance. Researchers typically use high-work-function noble metals as contact electrodes for p-type OFETs owing to transport levels well below −5.0 eV for ambient stable OSCs. This raises questions regarding the economic and environmental advantages of OSC based printed electronics. This study demonstrates high-mobility OFETs with copper contact electrodes using doped interlayers. A poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) interlayer was laminated on the OSC single crystals. The PTAA interlayer was chemically doped using aqueous doping solutions, followed by evaporation of copper contact electrodes. Our OFET showed a proper p-type operation with a mobility of 5.0 cm²V⁻¹ s⁻¹ and onoff ratio of approximately 10⁴. This is in contrast to the case without the doped interlayer showing poor performance and a low mobility of 0.2 cm²V⁻¹ s⁻¹. This study provides new opportunities for designing devices with a high performance, low cost, and material sustainability.