Hafnium Aluminate–Polymer Bilayer Dielectrics for Organic Light-Emitting Transistors (OLETs)

Organic light-emitting transistors are thin-film transistors capable of generating and sensing light under appropriate bias conditions. Achieving a low-voltage operation while maintaining high efficiency can be obtained by using high-mobility semiconductors, highly efficient emissive layers, and high-capacitance dielectrics. We report on the fabrication, dielectric characterization, and implementation of (organic/inorganic) bilayer dielectric stacks in green organic light-emitting transistors. Our dielectric stack includes a nanoscale hafnium aluminate layer fabricated by atomic layer deposition and a thin layer of a polymer dielectric. We found that the hafnium aluminate layer is amorphous in nature and highly transparent in all the visible range. The bilayer stack showed around 10 times higher capacitance per unit area than our polymer reference dielectric. When used as a dielectric in organic light-emitting transistors, this stack enabled low leakage current and operation below 20 V, with a threshold around 6 V and similar efficiencies. Thus, engineering the dielectric layer can enable the tuning of the device working conditions and performances while keeping robustness and negligible leakage values. Thus, these findings open the way to use nanoscale organic/inorganic bilayer dielectrics to enable low-bias, low-power consumption optoelectronic devices of relevance for next-generation electronics applications.