High Efficiency and Uniform Emission in Micropixelated Inorganic/Organic Hybrid Vertical Light-Emitting Transistors and Displays

Vertical light-emitting transistors (VLETs) fabricated by integrating organic vertical transistors and organic light-emitting diodes (OLEDs) have been proposed as a prospective building block for display technologies. However, organic vertical transistors normally have non-ohmic injection and a low-mobility channel, resulting in low VLET performance compared to the pristine OLED. The difficulty of fine patterning the source electrode and organic layer in a stacked VLET geometry has also been a technical issue limiting industrial applications. This paper reports on a simple approach to realize a high-performance, miniaturized VLET by using a highly conductive, well-designed inorganic transistor. Here, we investigate the ZnO transistor configured with an insulator-encapsulated source electrode to confine the current pathway in the VLET, which can be easily fabricated and integrated with various solution-processed or vacuum-sublimed inverted OLEDs (IOLEDs). This ZnO transistor exhibits ohmic contact and a high electron mobility of >10 cm2/(V s) that enables effective electron injection and lateral transport in the VLET, forming a millimeter-scale density gradient (channel depth) for strong surface emission. Furthermore, the high mobility of ZnO facilitates the design of a simple source pattern with a large aperture ratio on the ZnO area to control the current density and distribution and thus the VLET output. From a systematic study of the source design, we show that the ZnO transistor can be optimized to achieve homogeneously high conductivity in the ON state and yield the best VLET performance with maximum emission intensity and efficiency close to those of the IOLED, while the emission can be spatially uniform and precisely defined by the ZnO pattern. Finally, we implement a micropixelated VLET-based active matrix panel to demonstrate the prospect of high-resolution display applications.