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Donor-Acceptor light emitting exciplexes as materials for easily to tailor ultra-efficient OLED lighting

Periodic Reporting for period 2 - EXCILIGHT (Donor-Acceptor light emitting exciplexes as materials for easily to tailor ultra-efficient OLED lighting)

Reporting period: 2017-09-01 to 2019-08-31

Artificial lighting is a global and growing industry. New forms of efficient solid state lighting (SSL) in particular are rapidly gaining a market share. New OLED technologies can revolutionise this industry as they have done in displays because of their potential flexible structure, infinite tailoring of their properties, efficiency and high colour quality. In order to fully benefit from this huge market potential, Europe’s academia and industry are eager to develop new technologies and recruit highly qualified staff.

The high demand for OLED SSL lighting would however place drastic demand on the use of very rare and expensive iridium. EXCILIGHT set out to address these difficulties by exploring exciplex emitters and thermally activated delayed fluorescence (TADF) in OLEDs that were expected to enable the industry to replace Ir complexes whilst retaining ultrahigh efficiency and giving new possibilities to simplify OLED design. The EXCILIGHT network was launched to train 15 Early Stage Researchers (ESRs) with an innovative and multidisciplinary approach to be a new generation of scientists while at the same time integrating this new technology into the industry.

The overarching aim of this project was to develop “Donor-Acceptor light emitting exciplexes as materials which can be easily tailored for ultra-efficient OLED lighting” through the implementation of the multi-disciplinary EXCILIGHT ITN that combined the following training and scientific and technical objectives:

(1) Training of 15 European PhDs (ESRs) in innovative and multidisciplinary ways. The ESRs carry out the majority of their research work at their home institutions and spend secondments at other partners of the network. This includes working in industry to impart knowledge transfer and gain experience in the industrial research culture.
(2) Synthesis and characterisation of donor acceptor organic materials.
(3) Photophysical characterisation of exciplex systems and the TADF mechanism.
(4) Electrochemical and spectroelectrochemical characterisation of donor and acceptor organic materials.
(5) TADF OLED device fabrication and characterisation.
In this project we were exploring the use of exciplex based emitters with 100% efficiency through the use of thermally activated delayed fluorescence (TADF) in OLEDs.

A group of 15 PhD students were recruited and they were responsible for design and synthesis of new organic molecules, the analysis of the synthesised compounds and, finally, for the fabrication and characterisation of OLED devices. While the analysis of exciplex behaviour of commercially available compounds has been performed, the search for new efficient exciplex sets based on novel molecules advanced simultaneously.

The first 5 PhD students were successfully working on synthesis of several new compounds based on triazine, tetrazine, naphthalene imide etc. based compounds. Another 4 PhD students were working on electrochemical, spectroscopic and photophysical characterisation of commercially available and newly synthesised compounds for exciplex applications. The remaining 6 PhD students were working on different approaches in using exciplexes as efficient emitters. This included tasks ranging from stability optimisation, white device formation, and the formation of large area devices up to using printing, spin coating solution deposition process or (new in this area) organic vapour deposition processes.

There were several important results achieved during the project implementation such as setting up a new impedance technique to analyse charge carriers in OLED devices, an OLED lifetime measuring system and the formation of fully TADF exciplex based white OLED devices. In the end the main results was to present the description how to understand and optimize the exciplex emitters in order to obtain highly efficient exciplex based TADF OLED devices. All of these results bring us closer to fabrication of efficient OLED lighting devices.
EXCILIGHT has trained a multidisciplinary group of 15 ESRs to meet the future needs of academia and industry in the rapidly emerging area of OLED. The researchers acquired knowledge in research and development of new materials for OLED lighting, but also a broad experience in team working, working within industrial and academic settings in several EU Member States, to become the research leaders of the future in OLED.

The results of EXCILIGHT have already started to have an impact on the general public, on industry and on future research and will continue to do so:

(1) The general public will benefit from new, bendable OLED devices which use limited Iridium, making them environmentally friendly as well as lower-cost.
(2) A new generation of scientists with new sets of techniques to combine will be crucial for future research in OLED.
(3) A new generation of scientist will strengthen the European electronics industry.
Logo of the EXCILIGHT project
Some impressions from the EXCILIGHT project