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LEO Report Summary

Project ID: 644742
Funded under: H2020-EU.

Periodic Reporting for period 1 - LEO (Low-cost / energy Efficient Oleds for lighting)

Reporting period: 2015-01-01 to 2016-06-30

Summary of the context and overall objectives of the project

The LEO project ambitions innovative manufacturing concept & routes towards sustainable high performance bendable and low cost OLEDs for general and mood lighting, merging conventional and proven technologies with disruptive approaches (e.g. substrate, architecture, hybrid processing, layouts).
The general objective is to develop the technologies enabling the manufacturing of large area (>500 cm2) flexible top emission OLEDs (TE-OLEDs) on metal foils. For that purpose and to promote the development of highly emitting lighting devices, two different designs are considered, which combine either white warm and cold macro-pixels or red, green and blue mono-colour OLED stacks in a stripe configuration. The strong interest of the second approach could be to benefit from novel mono-colour OLED stack architectures bringing significantly enhanced light extraction, in particular.
In order to reach these ambitious goals, the LEO project gathers all the stakeholders of the OLED lighting device fabrication value chain, including substrate and organic materials suppliers (ArcelorMittal, Cynora), an OLED manufacturer (OSRAM) and recognized research centres in the field of OLEDs and life cycle analysis (CEA, CNR, Gaiker).
Since beginning of 2015, the LEO project activities are thus addressing various technological building blocks developments including (i) the development of low carbon steel foils adapted to OLED technologies, (ii) the integration of a more performing anode material as well as novel rare-earth metal-free OLED emitters, (iii) the development of novel solutions to enhance both light extraction and device durability, (iv) the development of an hybrid technology based on both dry and wet OLED stack deposition processes and (v) the integration and up-scaling of the different building block technologies in an industrial manufacturing environment.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

At project mid-term, the developments of the main technological building blocks mentioned above have globally well progressed with following results:
• Low carbon steel (LCS) substrates specifically engineered for OLED deposition are now available with dimensions up to ~18*18 cm2. This nice result was not expected at this early stage and goes beyond expectations. In the same manner, first proof of concept of an operational interconnected LCS substrate was achieved that requires however further development to ensure better electrical reliability and environmental stability.
• Various operational OLED devices have been successfully achieved by vacuum deposition (dry technology) on the LCS/epoxy substrates, validating the “OLED quality” of such LCS/epoxy foils. It includes arrays of 1cm2 green OLEDs on 5*5 cm2 LCS foils as well as 1.8 cm2 white OLEDs processed in an industrial environment.
• The interest of vacuum deposited Ag silver anodes was confirmed by the demonstration of +30% additional luminance with respect to conventional Al-based anodes. In the same manner, an advanced concept of top cathode based on WO3/Ag/WO3 was theoretically and experimentally demonstrated as bringing +50% light emission in mono-colour TE-OLEDs. In return, sprayed anode (Ag nano-inks) or cathode (Ag nanowires) are found extremely difficult to adapt to TE-OLED technology. In particular wet-deposited Ag anodes turn out to be not adapted because of excessive roughness and far too low reflectance.
• Successful integration by dry and hybrid technologies of rare-earth metal-free green emitters from CYNORA has been demonstrated at laboratory scale with rather interesting luminance performance, up to 46Cd/A (see Anand Verma et al.,Appl. Phys. A (2016) 122:191). Upscaling of this wet technology for 1cm2 TE-OLED on LCS substrates faces however short-circuit issues that may be related to insufficient anode surface quality and/or silver-pedot:pss incompatibility. As for dry technology, while 1cm2 TE-OLED processing on LCS is now routinely performed, it still requires strict control of anode cleanliness to get enhanced performance repeatability.
• A CEA proprietary Al2O3/hard coat multilayer encapsulation coating has been demonstrated to exhibit a very promising protection efficiency again humidity together with a good scratch resistance. This solution will be tested in industrial conditions very soon, first on rigid substrate (silicon) then on flexible LCS substrates.
• Finally, a cm2-wide PDMS light out-coupling microlens array membrane was successfully achieved, ready to be transferred on a TE-OLED for a further proof of concept.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

On the basis of these already promising results, the next project period will focus on the specific issues related to technology upscaling. Over the next few weeks, a key milestone to reach aims at demonstrating a fully evaporated large scale (25 cm2) white OLED on LCS/epoxy substrate, which could raise critical issues related to the management of surface defect density and long term environmental stability. At longer term, various demonstrators are scheduled to, at the end of the project, come to the manufacturing of two luminaire demonstrators that integrate the LEO technology. These demonstrators have been designed by 2 end-users, Artemide and Technology Luminaires, and take into account the recyclability requirements. An example of luminaire design is given below together with some of the technology building blocks that could be used to enhance the luminaire performances and its environmental sustainability.

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