The ratio of spontaneous emission inside a diode structure to that in free space is called the Purcell factor (F(λ)). The structure of organic light-emitting diodes (OLEDs) has a significant influence on the spontaneous emission rate of dipole emitters. Therefore, to describe the optical properties of OLEDs, it is essential to incorporate F(λ) in the description. However, many optical studies on OLEDs continue to be conducted without considering F(λ) for simplicity’s sake. Hence, in this study, using carefully designed bottom- and top-emitting OLEDs, we show that the external quantum efficiency obtained without considering F(λ) can be over- or under-estimated, and in some cases, the margin of error may be significant. We also reveal that the subtle distribution of the electroluminescence spectrum can be explained properly only by including F(λ). Both these results stipulate the importance of including F(λ) to maintain a quantitative agreement between theoretical and experimental data. Hence, the inclusion of F(λ) is important for designing OLEDs with enhanced efficiency or desired spectral characteristics.

Microdisplays based on organic light-emitting diodes (OLEDs) have a small form factor, and this can be a great advantage when applied to augmented reality and virtual reality devices. In addition, a ...

Graphene film can be used as transparent electrodes in display and optoelectronic applications. However, achieving residue free graphene film pixel arrays with geometrical precision on large area has been a difficult challenge. By utilizing the liquid bridging concept, we realized photolithographic patterning of graphene film with dimensional correctness and absence of surface contaminant. On a glass substrate of 100 × 100 mm ² size, we demonstrate our patterning method to fabricate an addressable two-color OLED module of which graphene film pixel size is 170 × 300 µ m ² . Our results strongly suggest graphene film as a serviceable component in commercial display products. The flexible and foldable display applications are expected to be main beneficiaries of our method.

Surface-exchanged, partially pyridine-functionalized colloidal quantum dot-based light-emitting diodes (QD-LEDs) that exhibit a low turn-on voltage and high brightness are reported. Pyridine is stochastically exchanged to a greater extent at the interface between the QDs and the hole transport layer via ligand exchange. Pyridine improves the charge balance within the QDs by enhancing the hole injection and hence lowers the turn-on voltage of the QD-LEDs. This strategy is applied to red-, green-, and blue-emitting (three primary colors) QD-LEDs. Pyridine-functionalized QD-LEDs (QD/py-LEDs) show enhanced maximum luminance, lowered driving voltages, and improved current- and power-efficiencies as compared with the original surface ligand-functionalized QD-LEDs. All three types of QD/py-LEDs show narrow emission spectra (full width at half maximum <40 nm) and cover 159% of the National Television System Committee 1987 color gamut.