Images courtesy of Adv. Funct. Mater., 25, 1955-1971, 2015.
A deeper picture of blue pixels
Organic electronics devices could have a major role to play in addressing contemporary social challenges like reducing CO2 emissions, yet some technical challenges remain before they can be more widely applied. We spoke to Dr Denis Andrienko about the MOSTOPHOS project’s work in investigating the issues which limit the stability of blue phosphorescent materials A relatively small
amount of material is required to produce AMOLED electronic displays, which are made of thin organic layers, making them an attractive option in certain electronic devices, including mobile phones, laptops and televisions. They also have some other beneficial attributes, as Dr Denis Andrienko of the MOSTOPHOS project, an EC-funded initiative bringing together both academic and commercial partners, explains. “AMOLED displays can be tuned fairly easily, by tuning the chemical structure of the emitter, or the entire pixel. Also, the power consumption, which is very critical for the display, is fairly low for an OLED. As a result, they don’t heat up much,” he outlines. However, there are also some limitations to consider. “If you look at a typical OLED display on the market, whether it’s in a TV or a mobile phone, you will see that there are three different pixels – red, green and blue. The green and red pixels, because of their lower excitation energy, are already phosphorescent. They harvest both triplet and singlet electronic states, which boosts their efficiency” says Dr Andrienko.
www.euresearcher.com
Blue pixels The same efficiency gains could potentially be achieved with blue pixels, yet in practice this is not currently the case, as blue light has a significantly higher excitation energy and hence there is a higher chance that an organic material will be damaged by the excitation. One of the key challenges in the organic electronics field is providing a high efficiency of blue pixels in a display, while at the same time ensuring that the lifetime is long enough to be used in a device, a topic central to the work of the MOSTOPHOS project. “That basically is the key point. The project is about figuring out what limits the stability of blue phosphorescent materials in OLEDs and providing chemical design rules for more stable deep blue emitters,” says Dr Andrienko. This work centres on developing a simulation framework, which will allow Dr Andrienko and his colleagues to look deeper into these stability-limiting mechanisms in phosphorescent OLEDs. “We’re working on a simulation platform,
which can in principle be used not only for blue phosphorescent OLEDs, but also to simulate other organic semiconducting devices” he continues. “We aim to provide feedback for organic chemists, helping them to synthesise structures with properties relevant to devices.” A good example could be a situation where a manufacturer wants to display a sky-blue colour in a device, or another that maybe wants their device to have a lifetime of 40,000 hours. Determining a material’s suitability in these terms can be a complex and expensive process, so Dr Andrienko and his colleagues aim to develop an efficient method of effectively pre-screening them. “The idea is basically to have a database of compounds, and to pre-screen those compounds before synthesising them. Synthesising and characterising materials for OLED applications is very time-consuming and expensive, so if we can reduce that cost using a computer simulation, then that would be a real asset to a company working on the design of this material,” he
19