An instrument for measuring the orientation and position (distribution) of excitons
Brief diagram of the equipment and photograph of the equipment
An example of the Measurement and Analysis
Comparison of measured p-polarization angle spectra (left figure and dots in right figure) and simulated spectra (solid lines in the right figure) to extract the horizontal orientation ratio by the fitting.
The horizontal dipole ratio (HDR) of an emitter has a profound effect on the efficiency and the angular spectrum (light emitting color and intensity). Horizontally oriented emitter gives 1.5 times higher efficiency than randomly oriented one.
Angle-resolved p-polarized EL (AREL) spectra from two OLEDs with different doping concentrations. This figure shows that the AREL spectra are well fitted with simulation results with the specific HDRs for the devices, indicating that the extracted HDR values are accurate to describe the AREL spectra.
Example of Exciton Distribution Analysis (s-polarization)
Figure 1. Device structure
Figure 2. Exciton density distribution extracted using the following measurement spectrum
Figure 3. Comparison of s-polarization AREL spectra with the simulated ones using the extracted exciton distributions shown in Figure 2.
Excellent fittings between the experimental data and simulation results using the exciton distributions extracted from the devices with two different doping concentrations indicate that JALS gives accurate exciton distribution in OLEDs.
Measuring the distribution of excitons within the emissive layer is crucial due to its significant influence on the device lifetime. Integrating this process with the device structure provides essential insights for developing long-lifetime devices, thereby offering vital information and accelerating the pace of research and development.
* References – Publications
Origin and Control of Orientation of Phosphorescent and TADF Dyes for High-Efficiency OLEDs
Kwon-Hyeon Kim and Jang-Joo Kim*
Adv. Mater. 2018, 30, 1705600
It has been known for decades that the emitting dipole orientation (EDO) of emitting dyes influences the outcoupling efficiency of organic light-emitting diodes (OLEDs). However, the EDO of dopants, especially phosphorescent dopants, has been studied less than that of neat films and polymer emitting layers (EMLs) due to the lack of an apparent driving force for aligning the dopants in amorphous host films. Recently, however, even globular-shaped Ir complexes have been reported to have a preferred orientation in doped films and OLEDs. External quantum efficiencies (EQEs) higher than 30% have also been demonstrated using phosphorescent and thermally activated delayed fluorescent dyes (TADF) doped in EMLs. Here, recent results on the EDO of phosphorescent and TADF dyes doped in host films, and highly efficient OLEDs using these dyes are reviewed. The origin and control of the orientation of phosphors are discussed, followed by a discussion of future strategies to achieve EQEs of over 60% without a light extraction layer, from the material point of view.