•Vertical heterojunction based on organic molecular semiconductors.•Top contact configuration with polymers as gate dielectrics.•Top-contact light emitting transistors of vertical heterojunctions are fabricated.•Hole transport and exciton recombination occur in different organic layers.•Modulation of drain current and light emission is realized under ambient atmosphere.We report a top-contact light emitting field-effect transistor based on an asymmetric vertical heterojunction using pentacene as a field-effect layer and tris-(8-hydroxyquinolinato) aluminum (Alq3) as an electron transport and luminescent material, which is fabricated on an indium tin oxide (ITO)-coated glass substrate with poly (methyl methacrylate) (PMMA) as a gate dielectric. The Alq3 layer underneath the drain electrode roughly occupies one half of the pentacene surface forming an asymmetric heterojunction with pentacene. A hole transport layer N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) is introduced to occupy the other half of the pentacene surface underneath the source electrode to allow vertical hole transport in the device. We have realized the electrical switching functionality of a field-effect transistor (FET) and the control of electroluminescence (EL) simultaneously under ambient atmosphere. The device exhibits typical p-channel characteristics and green emission from Alq3 is observed adjacent to the drain electrode. A working principle of the device is discussed in detail. Furthermore, this device configuration enables high-spatial-resolution fluorescence imaging of device operation, which is a simple and powerful tool for studying organic luminescent materials.

In this paper, the pentacene-based organic field-effect transistors (OFETs) with poly(methyl methacrylate) (PMMA) as gate dielectrics were fabricated, and the effects of gate dielectric thickness and semiconductor thickness on the device performance were investigated. The optimal PMMA thickness is in the range of 350–400 nm to sustain a considerable current density and stable performance. The device performance depends on the thicknesses of the active layer non-monotonically, which can be explained by the morphology of the pentacene film and the position of the conducting channel in the active layer. The device with a pentacene thickness of 50 nm shows the best performance, which has a maximum hole mobility of 1.12 cm2/V · s. In addition, the introduction of a thin layer of tris-(8-hydroxyquinolinato) aluminum (Alq3) to the OFETs as a light-emitting material greatly decreases the device performance.