Nitrogenous Interlayers for ITO S/D Electrodes in N-Type Organic Thin Film Transistors

Abstract

The commercialization of organic thin film transistors (OTFTs) is partly hindered by the high cost and stubborn work function (WF) of common Au source/drain (S/D) electrodes. In this work, indium tin oxide (ITO) S/D electrodes modified with three different nitrogenous interlayers including 1,4-bis(2-hydroxyethyl) piperazine (HEP), polyethylenimine ethoxylated (PEIE), and branched polyethylenimine (PEI) are adopted to fabricate n-type OTFTs. The WF of bare ITO is 4.7 eV, whereas ITO modified with nitrogenous interlayers exhibits WFs ranging from 4.1 to 3.6 eV. By the first-principle calculation and element analysis, the protonated amines are critical for the reduction of ITO surface WF. Besides, the interlayers with higher nitrogen contents are more likely to improve the wettability of octadecyltrichlorosilane (OTS) modified ITO substrates, and help to gain the continuous and oriented poly[2,5-bis(4-tetradecyloctadecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)-ethene] (P4FTVT-C32) semiconductor thin films. Therefore, P4FTVT-C32 based OTFTs with maximum electron field-effect mobility of 1.95 cm2 V−1 s−1 are achieved by PEI treatments. These results indicate that the ITO S/D electrodes modified by nitrogenous interlayers can greatly slash costs and promote commercialization of OTFTs.