Towards OCPLEDs: Organic Circularly Polarised Light Emitting Devices

Lead Research Organisation: Imperial College London
Department Name: Dept of Chemistry

Abstract

Organic light emitting diodes (OLEDs) require an emissive electroluminescent layer of an organic semiconductor material located between two electrodes, where at least one of the electrodes is transparent. Such devices are revolutionising display technologies, with the production of flexible and fully transparent devices possible. Devices that emit circularly polarised electroluminescence (CPEL) should have vast translational potential in photonic technology, such as highly improved LCD backlighting, colour-image detection and stereoscopic displays, optical communication, and quantum computing, however to date the problem of directly generating CPEL has not been solved. The goal of this research is to use intrinsically chiral, conductive and luminescent small molecules as electroluminescent layer in OLEDs, in an attempt to demonstrate efficient CPEL. Such work would have significant impact on current knowledge, which could be exploited in a number of translational areas. Taking alternative LCD backlighting as one example of the exploitation of this work, current technologies rely on polarising filters that effectively cut out 75% of the light used in these displays. Combined with absorption by the colour filters and at device interfaces, only 4% of the light used is transmitted. The use of a polarised light source, coupled with tuneable colour components would remove this need, thus leading to significantly more energy efficient displays, with a dramatically lowered carbon footprint.

Planned Impact

The science proposed herein would have significant impact on current academic and industrial knowledge in a diverse range of disciplines including chemistry, physics and materials science. Indeed, advances in the direct generation of CPEL would have international impact in these fields, and is likely to promote new research directions. The translational aspect of this proposal would be of high interest to a number key industrial companies (CDT, Merck, BASF, etc) involved in plastic electronics research. Technological advances resulting from this work would have clear ramifications in terms of wealth creation within the UK, with, for example, the current OLED market valued at >$2.5B. Taking alternative LCD backlighting as one example of the exploitation of this work (as highlighted in the proposal), a novel polarised light source, coupled with tuneable colour components would lead to significantly more energy efficient displays. Such displays with a lowered carbon footprint would be of clear environmental impact, and therefore of benefit to society as a whole. Finally, further training of skilled-coworkers and the educational experiences of students involved in this science would also have clear economic and societal impact.
 
Description The goal of this research was to use helical (single handedness) conductive molecules, as the electroluminescent layer in organic light-emitting diodes (OLEDs), in an attempt to make the light emitted circularly polarised (CP). We successfully developed and patented an approach to fabricate polymer-based light emitting diodes (PLEDs), using solution-processed materials, where the emission from the polymer is substantially CP. Our final and unique approach, simply added a helical small molecule dopant to a conventional achiral light-emitting polymer during processing. Without the chiral small molecule, the emission from the polymer was non-polarised. The core potential application of such CP-PLEDs is in flat panel displays (FPDs). Firstly, as an alternative LCD backlight, potentially doubling efficiency by halving the light lost at the first polariser layer. Secondly as the emitting elements in AM (Active matrix)-OLED displays, again potentially doubling efficiency by halving the light lost at the contrast enhancing CP surface filter.
Exploitation Route Our approach simply using a small molecule dopant to generate CP light is remarkably simple and highly translatable. It would make use of a conventional material set, device process flow and device architecture, but with the addition of a helical (chiral) molecular dopant to the light emitting polymer solution prior to its deposition: this changes PLED emission from non-polarised to circularly polarised. We (and others) will take this approach forward by further validating the approach, particularly studying the effect with other polymers, and optimising the devices to obtain key performance benchmarks. We believe the most industrially relevant application of our technology would be in the use of a CP-PLED for an LCD backlight or AMOLED display.
Sectors Chemicals,Electronics,Energy

 
Description Thus far, we are using our findings to further validate the technology in collaboration with a company (see IP and collaborations section). If we reach certain performance benchmarks, then it is highly likely that our collaborating company (or another) will license the IP and take the technology forward into display applications. These efforts will also lead to a number of follow on publications. The publications generated from this work have been cited a number of times already from those working in the chemistry, materials and organic device communities, thus impacting the knowledge economy.
Sector Chemicals,Electronics
 
Description EPSRC Established Career Fellowship
Amount £2,000,000 (GBP)
Funding ID EP/R00188X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2018 
End 02/2023
 
Description EPSRC Impact Acceleration Award
Amount £143,502 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 05/2014 
End 04/2015
 
Description EPSRC Responsive mode
Amount £780,485 (GBP)
Funding ID EP/P000525/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2017 
End 03/2020
 
Description EPSRC Responsive mode
Amount £355,948 (GBP)
Funding ID EP/L014580/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2014 
End 02/2017
 
Description CDT 
Organisation Cambridge Display Technology
Country United Kingdom 
Sector Private 
PI Contribution This collaboration is facilitated through a grant from the Imperial College EPSRC Impact Acceleration Account. I (together with Dr Alasdair Campbell) am leading the research efforts. Cambridge Display Technology have supplied state of the art polymer materials to test in our approach towards circularly polarised light emitting devices.
Collaborator Contribution As well as supplying materials, we have joint meetings with Cambridge Display Technology to discuss progress. If we reach certain benchmarks, it is highly likely Cambridge Display Technology will take the technology forward (likely via the licensing of our IP).
Impact None yet.
Start Year 2014
 
Title ELECTROLUMINESCENT COMPOSITIONS 
Description The present invention relates to compositions capable of emitting circularly polarized electroluminescence comprising an electroluminescent polymer and a chiral dopant, processes for the synthesis of such compositions and light emitting devices incorporating such compositions. 
IP Reference WO2014016611 
Protection Patent granted
Year Protection Granted 2014
Licensed No
Impact Opportunities are still being explored.
 
Description Conference/Symposium lecture on the results of the grant 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I have given numerous lectures all over the world reporting the results of this award. The primarily outcome was dissemination of the research
Year(s) Of Engagement Activity 2013,2014,2015,2016,2017,2018,2019
 
Description Press release and online video 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact We produced a video to publicise the results of the research together with a press release
Year(s) Of Engagement Activity 2013
URL http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_29-7-2013-16-37-53