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Industrial manufacturing of conductive, transparent and flexible electrodes with nanoinks for organic electronic devices such as OPV and OLED lighting

Periodic Reporting for period 5 - CLEARSILVER (Industrial manufacturing of conductive, transparent and flexible electrodes with nanoinks fororganic electronic devices such as OPV and OLED lighting)

Reporting period: 2018-09-01 to 2019-02-28

Nowadays, Indium Tin Oxide (ITO) is the main material used for transparent conductive films (TCF). These films have significant drawbacks such as fragility, indium depletion and high manufacturing cost. A promising alternative is a conductive patterned Ag grid based covered with a protective ZnO nanolayer. To accelerate the uptake of this technology, the printed electronics market needs a complete solution of industrial inks and inkjet printing at large scale and high speed. This is the objective of CLEARSILVER proposed by KELENN Technology (KT) - manufacturer of industrial solutions for inkjet printing - and GenesInk (GNK) - leader on the conductive and semi-conductive nanoinks market.

Main achievement of CLEARSILVER are listed below:
• Providing a highly conductive TCF manufacturing solution to OPV and OLED markets.
• Offer a cost-effective process by direct patterning with inkjet printers for conductive designs.
• Develop a solid alternative to ITO based TCF based on Ag grids and ZnO nanoinks.
• Transposing printed TCF technology from pilot scale to industrial scale.
• Enabling the use of nanoinks at industrial scale.
• Developing an industrial inkjet printing solution with a high printing speed.

All along the project, GNK and KT managed to develop an alternative to ITO. GNK developed Ag and ZnO nanoinks for OPV and OLED applications. GNK and KT worked together to adapt GNK inks to KT industrial inkjet printer. KT managed to develop a R2R printing machine for TCF manufacturing. OLED and OPV devices were realized with success at the end of the project. CLEARSILVER solution proved to be an economic and technical viable alternative to ITO.
Pilot line for ZnO NPs manufacturing was implemented and is now operational. Tests are ongoing to optimize the synthesis of ZnO NPs. Indeed, purification of NPs will be performed by a membrane filtration system. The aim of this process is to simplify the purification of NPs via a 1 step filtration instead of the 4 steps of decantation in the actual process on pilot line. ZnO NPs and nanoinks having the same characteristics as ZnO NPs produced and purified by decantation were obtained by ultrafiltration at lab and large scales . This indicates that the membrane ultrafiltration process can be used to produce ZnO NPs thus replacing 5 decantation steps by 1 single step filtration. This new developed process will decrease the production duration of ZnO NPs by a factor of 3 minimum and allow to enhance the production capacity then by a factor of 3. Methanol used during filtration was also recycled and purified from all possible impurities.
Synthesis of Ag NPs was upscaled. Synthesis can be performed now on a 4 liters reactor (batch size). We achieved to enhance the quantity of Ag NPs produced per batch from 2 g to 67 g. During period 3, GNK started the development of a new inkjet Ag ink based on commercial crude Ag nanomaterials. 3 developed inks were considered as promising and were selected for further optimization and printing tests during period 4. The optimized ink was then qualified and will be launched before the end of the year. Some optimizations may be required according to our customers feedback. During the last period of the project, a new Ag inks for OPV and OLED compatible with PEDOT:PSS was also developed. This ink shows very good efficiency results. Fine tuning of the formulation must be realized to allow better printability by inkjet printing. The pilot mixer for Ag nanoinks manufacturing was ordered and it is expected to be installed at GNK on May 2019. GenesInk’s facilities are nowadays under restructuring to allow the installation of the new pilot mixer. The Life Cycle Assessment of ZnO and Ag NPs and nanoinks was realized. It allowed to quantify the environmental potential impacts of the different materials (Ag and ZnO nanoparticles and nanoinks) as well as impacts associated to the final printed product developed, i.e. Transparent Conductive Films for OLED and OPV applications.
Functional OLED and OPV devices were manufactured and CLEARSILVER technology was proven adapted and adequate for transparent electrodes in OLED and OPV devices.
Over the past 30 months, KT and GNK worked together to provide to the market an industrial solution for ITO replacement. Several steps were essentials to achieve this multidisciplinary project. At the beginning of the project a S2S printer was developed by KT. This printer was made to validate the process for CLEARSILVER. GNK developed a pre-industrial line for production of ZnO ink and nanosilver ink. After first results, project consortium scaled up the solution and developed an industrial line for production of nanoparticles functional inks and a R2R industrial printing solution. This industrial solution allowed to print TCF for OLED and OPV applications which were confirmed by functional devices fabrication by the Fraunhofer FEP institute. Final costs simulation with validated production rate highlight that CLEARSILVER project is an innovative and affordable solution for ITO’s market replacement.
The next generation of TCF must be lightweight, flexible, cost effective and compatible with large scale manufacturing. These requirements seriously limit the use of ITO as transparent conductor because ITO films deposition methods are expensive and time consuming. Finally, ITO films lack of flexibility and indium is a scarce material. The OPV and OLED lighting applications is the first targeted market. The next mid-term step (5 years), after the integration of the technology by these early adopters, will be the flexible displays market.

The CLEARSILVER project will open the field of new possibilities for the entire printed electronic value chain. The foreseeable expected impacts are:

• To create new markets for GNK as nanoinks supplier and for KT as electronic printer manufacturer.
• To participate to the development of a competitive European printed electronics (PE) value chain.
• To promote closer collaboration between an ink supplier, an equipment manufacturer and end-users, addressing the full value chain and leading to a competitive advantage in the market introduction of the final products.
• To bring the flexible PE technology from lab to fab.

Ag and ZnO nanoinks from Genes'Ink are nowadays commercialized and known for their very high performances in OLED, OPV and connectivities applications. Development are still ongoing to enhance the performances mainly the conductivity and the printing resolution. Besides, parallel optimization tests are performed on pilot line to enhance the production capacit to 25 liters ink/batch especially for Ag nanoink. So far, first Ag grids were printed and evaluated. Lines with a width varying from 40 µm to 100 µm were successfully printed. Transparencies as high as 85% were obtained. Sheet resistance were evaluated to be as low as 15 mOhm/sq.

A sheet to sheet inkjet printer was developed in the framework of the project. The R2R PR800 was assembled during February 2018