Fabrication and Characterization of Inverted Organic Light-Emitting Diodes With Low Driving Voltage Utilizing Upconversion Process

Reducing the driving voltage of organic light-emitting diodes (OLEDs) is crucial for their widespread applications. Here, we fabricate inverted OLEDs based on an upconversion (UC) process mediated by triplet-triplet annihilation for the development of solution-processable and air-stable OLEDs with a low driving voltage. We used a soluble naphthalene diimide-based n-type polymer semiconductor of N2200 for the solution processing of an accepter layer, on which a donor layer composed of rubrene was fabricated by thermal evaporation. The fabricated OLEDs emit light with the peak wavelength of 565 nm by application of a low voltage exceeding 1.5 V, indicating the formation of charge transfer excitons at the donor/acceptor interface and the subsequent UC process in the rubrene emitter.