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The efficient conversion of electron-hole (e-h) pairs into triplet excitons is a challenge for blue organic light-emitting diodes (OLEDs) based on triplet–triplet annihilation upconversion (TTAUC). The 25% fraction of e-h pairs that create singlet excitons represents a significant loss channel that can lead to parasitic red-shifted emission. In this study, an intermolecular intersystem crossing that relies on a “dark sensitizer” (DS) layer consisting of tris-(8-hydroxyquinoline)aluminum (Alq3) doped with tris[2-phenylpyridinato-C2,N]Iridium(III) (Ir(ppy)3) is demonstrated to enhance the TTAUC process. Carriers recombination and excitons generation are formed on Alq3 molecules. Alq3 singlet excitons are then quenched by the Ir(ppy)3 triplet state, followed by energy transfer to the Alq3 triplet state. The non-emissive, long-lived Alq3 triplets migrate from the sensitizer layer to an emitter layer where they undergo TTAUC to give blue fluorescence emission. This DS-TTAUC process promises no green emission from the Alq3. The efficiency of a blue OLED utilizing DS-TTAUC was improved by 34.2% compared to a standard TTAUC OLED. In addition, the device exhibited CIE coordinates of (0.15, 0.09). Furthermore, a high photoluminescence quantum yield fluorescence emitter is incorporated to enhance the singlet exciton emission in the emitter layer. A maximum external quantum efficiency of 7.54% can be achieved with recorded-high quantum yield of the TTAUC (ΦTTAUC) = 37.6% in solid state.

The enhanced device performance of blue quantum dot light-emitting diodes (QD-LEDs) was demonstrated; a positive aging process was used to improve electron transport and suppress electroplex emission, which results from the interface between the QD-emitting layer and the ZnO electron-transporting layer (ETL). This electroplex interface functions as a low-energy recombination center, leading to energy loss and further decreasing the device performance. Without the positive aging process, the QD-LED exhibited poor electrical and electroluminescent (EL) characteristics, as well as an EL spectrum containing a strong electroplex emission with a peak at 635 nm. A positive aging process was applied by dripping a surface active reagent on the cathode before device encapsulation. The active reagent treatment led to suppression of the electroplex emission and enhanced device performance by promoting Al atoms into ZnO ETL to facilitate electron transport at the QD/ZnO interface. Furthermore, static positive aging was investigated by assessing the QD-LEDs at different storage times to observe the maturing process. After 409-hrs of maturing, the QD-LEDs exhibited an optimal device performance with favorable CEmax and EQEmax values of 6.2 cd/A and 8.7%, respectively. At a current density of 1 mA/cm2, the QD-LED exhibited a maximum overall efficiency enhancement factor of 7.1 after the positive aging process. In particular, electroplex suppression was correlated with the enhancement of device performance, caused by an upgraded QD/ZnO interface, formed during the positive aging process, benefits the electron transport.