Title: Investigation of the Crystalline Emitting Layers Exhibiting Emission Facilitated by Triplet States for White Organic Light Emitting Diodes
Research proposal No: 1.1.1.9/LZP/1/24/140
Duration: 01.04.2025.-31.03.2028.
Project Leader: Oleksandr Bezvikonnyi
Total budget: 184 140 EUR
European Regional Development Fund (ERDF) funding: 156 519 EUR
ISSP UL budget: 9207 EUR
Project description:
The biggest obstacle to the dominance of the technology of white organic light emitting diodes (WOLED) in the market of lighting and displays is low efficiency and stability. The project aims to develop efficient crystalline OLEDs. These devices will utilize emitters exhibiting crystallinity in emitting layers and triplet-facilitated emission. The phenomena like thermally activated delayed fluorescence (TADF), room temperature phosphorescence (RTP), etc. are prioritized as non-toxic, environmentally friendly approaches. State-of-the-art efficiency and stability will be pursued by using newly designed and synthesized crystalline organic semiconducting (COS) compounds with highly oriented dipoles, high drift mobility of charge carriers, and enhanced morphological features. Molecular packing of COS facilitated by crystallization in emitting layers will be used for the enhancement of the efficiency of WOLEDs with target values of 30% of external quantum efficiency (EQE) and color rendering index (CRI) of 90. The target values will be achieved by optimization of the device structure incorporating different emitting layers systems, transport layers, thickness of the layers to improve the charge balance, out-coupling and the quality of the white light.
This project focuses on the development of efficient white organic light emitting diodes (WOLEDs) utilizing emitting organic semiconductors exhibiting crystallinity in emitting layers of the devices and utilizing triplet excitons in electroluminescence. The main goals of the project include design, synthesis and characterization of the crystalline organic emitters exhibiting triplet-facilitated phenomena like thermally activated delayed fluorescence (TADF), room temperature phosphorescence (RTP), etc. The target values of the OLEDs based on the emitters are external quantum efficiency (EQE) of 30% and white light with the color rendering index (CRI) of 90.
The project is implemented at the Institute of Solid State Physics of the University of Latvia from 01.04.2025. until 31.03.2028. The total cost of the project is 184,140.00 EUR.
PROJECT PROGRESS
Time period: 01.04.2025. – 31.08.2025.
During the period of time, the postodoctoral student started to work as a visitor researcher at the Institute of Solid State Physics of the University of Latvia, familiarized himself with the internal regulations and safety procedures and gained access to work in the facilities.
The measures were undertaken by the postdoctorant and partner institutions of the project for the development of the donor-acceptor organic semiconductors exhibiting phenomena of thermally activated delayed fluorescence (TADF) with the possibility of occurrence of other triplet-facilitated phenomena like room temperature phosphorescence (RTP). In accordance with the project plan and in collaboration with the project partner institution Lviv Polytechnic National University and their cooperators, several series of promising compounds were synthesized in the scope of utilization of their crystallinity properties and triplet-facilitated emission.
One of the series is cyanopyridine-based derivatives with different electron donor moieties attached, like phenoxazine, phenothiazine, dimethylacridine and tert-butylcarbazole that are selected for achieving thermal stability, high charge transport and quantum efficiency of the compounds. The donor-acceptor structure must ensure the minimization of the overlap of the highest occupied and lowest unoccupied molecular orbitals, HOMO and LUMO, respectively, stimulating TADF. The scientific group of the partner institution Linköping University works on the theoretical calculations using the density functional theory, which were at the basis of the design strategy and will be continued to explore the distribution of the excited states and their correlation with emissive and crystallinity properties.
Another series is diaminobenzophenone derivatives with four fluorene arms aiming at high hole drift mobility, TADF property due to donor-acceptor interactions (Figure 2a). Differential scanning calorimetry (DSC) scans revealed that one of the compounds of the series exhibits a crystallinity peak making it a promising candidate as the crystalline organic semiconductor for the project implementation.
Several other design strategies are considered during the development of the compounds based on literature review and theoretical calculations. Their synthesis is ongoing.