**Abstract**

The inherent complexity of the structures of active-matrix (AM) organic lightemitting diode (OLED) displays severely limits not only their size but also device performance. Surface-emitting organic light-emitting transistors (OLETs) may offer an attractive alternative to AM displays. We report some characteristics of vertical-type OLETs (VOLETs) composed of a source electrode of low-dimensional materials and an emissive channel layer. With a functionalized graphene source, it is shown that the full-surface electroluminescent emission of a VOLET can be effectively controlled by the gate voltage with a high luminance on/off ratio (104 ). The current efficiency and effective aperture ratios were observed to be more than 150% of those of a control OLED, even at high luminances exceeding 500 cd m<sup>−</sup><sup>2</sup> . Moreover, high device performance of micro-VOLET pixels has been also successfully demonstrated using inkjet-patterned emissive channel layers. These significant improvements in the device performance were attributed to the effective gatevoltage-induced modulation of the hole tunneling injection at the source electrode.

**Keywords:** organic light-emitting diode (OLED), organic light-emitting transistor (OLET), vertical-type OLETs, graphene, on/off ratio, aperture ratio, inkjet printing, tunneling injection
