Monolayer graphene is used as an electrode to develop novel electronic device architectures that exploit the unique, atomically thin structure of the material with a low density of states at its charge neutrality point. For example, a single semiconductor layer stacked onto graphene can provide a semiconductor-electrode junction with a tunable injection barrier, which is the basis for a primitive transistor architecture known as the Schottky barrier field-effect transistor. This work demonstrates the next level of complexity in a vertical graphene-semiconductor architecture. Specifically, an organic vertical p-n junction (p-type pentacene/n-type N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C 8 )) on top of a graphene electrode constituting a novel gate-tunable photodiode device structure is fabricated. The model device confirms that controlling the Schottky barrier height at the pentacene-graphene junction can (i) suppress the dark current density and (ii) enhance the photocurrent of the device, both of which are critical to improve the performance of a photodiode.

In organic hole-transporting material (HTM)-based p−i−n planar perovskite solar cells, which have simple and low-temperature processibility feasible to flexible devices, the incident light has to pass through the HTM before reaching the perovskite layer. Therefore, photo-excited state of organic HTM could become important during the solar cell operation, but this feature has not usually been considered for the HTM design. Here, we prove that enhancing their property at their photo-excited states, especially their transition dipole moments, can be a methodology to develop high efficiency p−i−n perovskite solar cells. The organic HTMs are designed to have high transition dipole moments at the excited states and simultaneously to preserve those property during the solar cell operation by their extended lifetimes through the excited-state intramolecular proton transfer process, consequently reducing the charge recombination and improving extraction properties of devices. Their UV-filtering ability is also beneficial to enhance the photostability of devices.

Quantum dot light-emitting diodes (QLEDs) are expected to be the basis of next-generation displays and have consequently been extensively investigated with the aim of commercialization. Herein, QLED brightness, efficiency, and lifetime are significantly improved by insertion of an Al2O3 barrier layer via atomic layer deposition (ALD), which effectively suppresses the etching reaction with poly­(3,4-ethylenedioxythiophene):polystyrenesulfonate and prevents metal ion diffusion from indium tin oxide (ITO) into the emission layer, thereby effectively reducing the effect of exciton quenching. The above-mentioned suppression of exciton quenching is verified using time-resolved photoluminescence spectroscopy/energy-dispersive X-ray spectroscopy, and a device prepared using four ALD cycles is shown to exhibit increased maximal luminance (39 410 cd/m2; two times the value achieved without the Al2O3 layer), current efficiency (47.89 cd/A; eight times the value achieved without the Al2O3 layer), and external quantum efficiency (12.89%). In addition, all Al2O3-containing QLEDs feature longer lifetimes than the QLED without Al2O3.

We demonstrate, for the first time, the use of a solution-processed reduced graphene oxide (rGO) layer as a work function tunable electrode in vertical Schottky barrier (SB) transistors. The rGO electrodes were deposited by simple spray-coating onto the substrate. The vertical device structure was formed by sandwiching a N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) organic semiconductor between rGO and Al electrodes. By varying the voltage applied to the gate electrode, the work function of rGO and thus the SB formed at the rGO-PTCDI-C8 interface could be effectively modulated. The resulting vertical SB transistors based on rGO-PTCDI-C8 heterostructures exhibited excellent electrical properties, including a maximum current density of 17.9 mA/cm2 and an on–off current ratio >103, which were comparable with the values obtained for the devices based on a CVD-grown graphene electrode. The charge injection properties of the vertical devices were systematically investigated through temperature-dependent transport measurements. Charge injection was dominated by thermionic emission at high temperature. As the temperature decreased, however, impurity state-assisted hopping occurred. At low temperature and negative gate voltage, the reduced width of barrier induced by a high drain voltage yielded Fowler–Nordheim tunneling at the interface. The use of scalable solution-processed rGO as a work function tunable electrode in vertical SB transistors opens up new opportunities for realizing future large-area flexible two-dimensional materials-based electronic devices.

This paper introduces a strategy to modulate a Schottky barrier formed at a graphene–semiconductor heterojunction. The modulation is performed by controlling the work function of graphene from a gate that is placed laterally away from the graphene–semiconductor junction, which we refer to as the remote gating of a Schottky barrier. The remote gating relies on the sensitive work function of graphene, whose local variation induced by locally applied field effect affects the change in the work function of the entire material. Using Kelvin probe force microscopy analysis, we directly visualize how this local variation in the work function propagates through graphene. These properties of graphene are exploited to assemble remote-gated vertical Schottky barrier transistors (v-SBTs) in an unconventional device architecture. Furthermore, a vertical complementary circuit is fabricated by simply stacking two remote-gated v-SBTs (pentacene layer as the p-channel and indium gallium zinc oxide layer as the n-channel) vertically. We consider that the remote gating of graphene and the associated device architecture presented herein facilitate the extendibility of graphene-based v-SBTs in the vertical assembly of logic circuits.