Extremely efficient sky-blue organic electroluminescence with external quantum efficiency of ≈37% is achieved in a conventional planar device structure, using a highly efficient thermally activated delayed fluorescence emitter based on the spiroacridine-triazine hybrid and simultaneously possessing nearly unitary (100%) photoluminescence quantum yield, excellent thermal stability, and strongly horizontally oriented emitting dipoles (with a horizontal dipole ratio of 83%).

Linking topology in oligocarbazoles (see figure) has a strong influence on their electronic properties. 3(6),9′‐linked oligocarbazoles exhibit unusual suppression of electronic coupling between units, leading to localized excited states and very small reduction of triplet energies (compared to the monomer). Coupled with their excellent morphological stability, this makes them suitable as host materials for blue electrophosphorescence devices.

The combination of rigid acridine donor and 1,8-naphthalimide acceptor has afforded two orange-red emitters of NAI-DMAC and NAI-DPAC with high rigidity in molecular structure and strongly pretwisted charge transfer state. Endowed with high photoluminescence quantum yields (Φ ), distinct thermally activated delayed fluorescence (TADF) characteristics, and preferentially horizontal emitting dipole orientations, these emitters afford record-high orange-red TADF organic light-emitting diodes (OLEDs) with external quantum efficiencies of up to 21-29.2%, significantly surpassing all previously reported orange-to-red TADF OLEDs. Notably, the influence of microcavity effect is verified to support the record-high efficiency. This finding relaxes the usually stringent material requirements for effective TADF emitters by comprising smaller radiative transition rates and less than ideal Φ s.

We report a model of the carrier transport and the subgap density of states in amorphous InGaZnO 4 ͑a-IGZO͒ for device simulation of a-IGZO thin-film transistors ͑TFTs͒ operated in both the depletion mode and the enhancement mode. A simple model using a constant mobility and two-step subgap density of states reproduced well the characteristics of the a-IGZO TFTs. a-IGZO exhibits low densities of tail states and deep gap states, leading to small subthreshold swings and high mobilities.

Optical characteristics of microcavity organic light-emitting devices ͑OLEDs͒ having two metal mirrors are examined. Analyses show that a high-reflection back mirror and a low-loss high-reflection exit mirror are essential for such microcavity devices to obtain luminance enhancement relative to conventional noncavity devices. An enhancement of 2 in cd/A efficiencies has been experimentally achieved for microcavity top-emitting OLEDs using an exit mirror composing thin metal and dielectric capping. The capping layer in the composite mirror plays the role of enhancing reflection and reducing absorption loss, rather than enhancing transmission.