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.