Novel blue emitters for high-efficiency state-of-the-art OLEDs
Organic light-emitting diodes (OLEDs) are the dominating technology in contemporary small- and medium-sized displays, used for all smartphones or smartwatches. The technology offers flexibility, high color purity and simple processing. However, the bottleneck of OLED is the blue component, which is neither efficient nor stable today. Here, the energy associated with blue light is comparable to the chemical binding energies between covalently bound atoms in organic blue emitters. This causes molecular bond cleavage, which leads to reduced device efficiencies and lifetimes of the blue pixels in displays. Known issues like OLED TV burn-in and long-term color change become apparent, furthermore, low efficiency also means shorter device battery lifetimes. Thus, solving the issue of inefficient blue is the holy grail of OLED research.
OLEDs typically consist of several functional organic layers sandwiched between two electrodes. Arguably the most important layer in the device is the emitting layer, which typically consists of two materials – the host (matrix) and the guest (emitter). Co-evaporation ensures controlled doping of the emitting layers, typically in the concentration range of 1-20 wt%. The choice of the host material is as imporant as the choice of the emitter, as an incompatable host may lead to loss of efficiency and quick degradation of the device.
The student will be working at the IAP with novel state-of-the-art blue emitters, provided by the start-up beeOLED. Unlike all other approaches, those emitters are based on an intrametallic transition, which simply avoids the chemical instabilities of the conventional blue emitters altogether. The aim of the master thesis is twofold: firstly, understanding the photophysical (PL) properties of thin host-guest films with those new emitters, and secondly, applying the findings and manufacturing highly efficient blue OLEDs by way of solution processing and thermal evaporation. The PL characterization gives direct insight into how the emitter will perform in devices. The choice of a good host material for the emitters investigated as well as a suitable emitter concentration will be determined by the student, following a thorough photophysical investigation of thin-film samples: measurement of quantum efficiency, emission and absorbance spectra, and excited state lifetime. Based on the findings, the student will carry out OLED manufacturing using the appropriate host-guest combination, with subsequent device characterization.
As a result, the student will become well-acquainted with the organic semiconductor research field, gaining valuable lab experience as well as fundamental knowledge. The LEXOS research group has a great deal of expertise in the field of organic electronic devices, which creates a unique opportunity for carrying out cutting-edge research. Working closely with beeOLED, the student will specifically benefit from firsthand knowledge of state-of-the-art display technologies, very close to end consumer applications. In fact, it may well be that materials investigated here will end up in the next generation of smartphones.