The Japanese chemical company Sumitomo Chemical has joined Holst Centre‘s shared research programme on printed OLED devices.

Sumitomo’s involvement will advance efforts to develop manufacturing processes for low-cost, flexible OLEDs. Sumitomo is a supplier of materials for polymer OLEDs and had acquired Cambridge Display Technology several years ago to strengthen its activity in the field.

Much of today’s commercialised OLED display and lighting products are manufactured by depositing numerous thin layers of materials onto glass substrates or flexible plastic foils. Today’s highest-efficiency OLEDs are made using evaporative processes in vacuum conditions. Switching to atmospheric-pressure solution-based processes could reduce the cost of OLED manufacturing, removing the need for expensive vacuum equipment and reducing the wastage of costly OLED materials.

Shared development

Developing these solution-based processes is a key goal for Holst Centre’s Printed Organic Lighting and Signage programme. In order to introduce solution processing into the current production lines of end manufacturers, it is important to bring all players across the value-chain together to jointly develop a process which can be introduced in existing production.

Holst Centre’s Shared Innovation concept aims to bring these parties together to create a critical mass for such commercial introduction, explains Ton van Mol, partnership director at Holst Centre. ‘The fact that Sumitomo is now increasing its focus on OLED materials might speed up the market entry since end manufacturers will be increasingly confident to have companies that can supply them with the necessary materials,’ he adds.

With the recent conclusion of a Merck-led project in Germany to develop printable OLED materials, activity in the field is intensifying. But it will be a gradual transition. According to van Mol: ‘The expectation is that in the coming 2-3 years, some commercial products will contain a solution processed layer.’

In displays and signage the most likely candidates are the emitter molecules in an RGB display, whereby inkjet printing of the emitter layers instead of evaporation through a metal mask will allow better scalability and potential better resolution. However, the other layers in the OLED stack will continue to be evaporated. In the lighting field the most likely first candidate for printing is the hole injection layer. For both display and lighting devices in future it is expected that gradually more and more layers will be based on solution processing to allow for costs to come down.

This IP pipeline agreement ushers in a new phase of partnership between NUS and CDT that will create fundamental innovations in the science and technology of P-OLED displays and lightings. This  will hasten the development of higher performance and more energy efficient P-OLED devices. Under the terms of this agreement, CDT will be able to access the innovation stream arising from ONDL, with options to take licenses in existing and new IPs in P-OLED displays and lighting, solar cells and thin film transistor circuits.  Their commercialisation of these activities will generate a royalty stream back to NUS. The university will further benefit from the leverage on the considerable amount of expertise in CDT to address the most critical scientific challenges with the broadest impact.

“This IP pipeline licensing agreement is the natural next step in our partnership with CDT. CDT provides the best vehicle to commercialise our innovations. Furthermore new creativity and the entrepreneurial spirit will be stimulated in our students and post-docs through the vibrant interactions with this dynamic technology company”, said Assoc Prof Peter Ho, who is the co-Director of NUS Organic Nano Device Laboratory.

Dr. Jeremy Burroughes, Chief Technology Officer for CDT commented: “CDT has worked with Professor Ho since 1997 when he was at the Cavendish Laboratory, University of Cambridge. He has now built up an impressive research group in Singapore working on various Organic Device Technologies. We are delighted that this agreement allows us to enter a new phase of cooperation with him, his group and the National University of Singapore”.

The Engineer magazine makes Technology & Innovation Awards annually to recognise organisations demonstrating excellence in technology, innovation and collaboration. CDT’s award was presented in the Environmental Technology category as PLED lighting could significantly improve energy efficiency. Thorn Lighting, which shared the award with CDT and Durham University, points out that artificial lighting consumes almost 20% of all electrical power generated, and therefore produces a significant amount of carbon dioxide – around 2 billion tonnes globally every year.

PLED devices also operate at very low DC voltages – typically around 4V – making them suitable for integration with emerging renewable power and battery technologies, such as photovoltaics and high capacity lithium ion batteries.

The Engineer commented: “The rapid advance of LED technology over the last few years – and its energy saving possibilities – gives it the clear potential to become the dominant form of lighting in the near future. For global supplier Thorn Lighting and CDT, the possibilities offered by and the high-volume printing process used to manufacture them were an exciting prospect.”

“We are naturally thrilled that the work of our collaboration team has been recognised in this award”, said Jim Veninger, General Manager of CDT. “PLEDs are at the forefront of energy efficient lighting technology and offer clear advantages in manufacturability.”

Thorn Lighting’s Group Leader Dr Geoff Williams said: “CDT are the world leaders in light emitting polymers so we weren’t starting from scratch; they had 20 years of high level research knowledge to bring to the project.”

PLEDs are a form of OLED (organic light emitting diodes) based on long chain polymers rather than small organic molecules. PLEDs have the important advantage that they can be manufactured by printing from solution onto a substrate at atmospheric pressure, instead of requiring thermal evaporation in a vacuum.

Topless is an acronym for ‘Thin Organic Polymeric Light Emitting Semiconductor Surfaces’. The £3.3m Topless project was funded by a 50 per cent investment from the TSB. The consortium has now begun the next stage of research: a £4.3m programme named ‘Topdrawer’, aimed at understanding the manufacturability of lighting panels.

As a member, CDT will connect to the faculty expertise and highly trained students and graduates of the Center as well as an international network of partners in the field of organic photonics and electronics. This includes receiving insider information on the latest research and discoveries and invitations to exclusive events.

When asked about joining the program, Jeremy Burroughes, Chief Technical Officer of CDT stated, “COPE is a centre of excellence which CDT is very pleased to be involved with. It has impressive range of people and activities backed up with unique facilities. “

CDT’s mission is to develop solution processible OLEDs for lighting and displays as well as backplane technology for OLED displays. It is also active in organic thin-film transistor (OTFT) development and maintains interest in other plastic electronic technologies.

“CDT is increasing its involvement with Universities worldwide, in order to access technologies that could be of use, and to also strengthen its links with key University staff who can advise CDT”, Burroughes added. “Being a member of COPE community allows us to start developing our relationship with Georgia Tech and therefore supports the goal of greater University engagement.”

Bernard Kippelen, Co-Director of the Center commented, “I am delighted that Cambridge Display Technology has joined COPE’s Industrial Affiliates Program. CDT is a leader in the development of light-emitting polymer technology and I am convinced that future interactions with COPE’s faculty, students, and scientists will be mutually productive.”

The goal of the two-year collaboration is to apply Semprius’ patented semiconductor printing technology to improve performance of backplanes, which hold the electronic components that drive display screens for computers, televisions and a host of other devices. CDT, a wholly-owned subsidiary of Sumitomo Chemical, is a leader in the research and commercialization of polymer OLEDs and their application in displays.

Semprius’ micro-transfer printing process allows transfer printing of high-performance semiconductors onto virtually any surface, including glass, flexible and rigid plastic, metal and other semiconductor materials. Semprius will focus on using its patented process to transfer single crystal silicon semiconductors onto the backplane, thereby increasing overall display performance.

“Our technology provides higher performance at equal or lower cost,” said Joe Carr, CEO of Semprius. “The agreement with CDT gives us the opportunity to apply micro-transfer printing to advance backplane performance and manufacturing efficiencies.”

CDT will integrate this new backplane technology into their 14-inch development line at the company’s Godmanchester campus near Cambridge, UK.

“High-quality, high-mobility TFT backplanes are essential to achieve optimal
performance from OLEDs,” said David Fyfe, CEO of CDT. “The Semprius technology, using single crystal silicon semiconductors, offers potential for a low-capital, low-cost approach to achieving this, and we are very excited to be exploring its application to polymer OLED displays.”

The rapid development of organic electronics is mainly driven by applications that require low cost electronic circuits covering large areas with mechanical flexibility. Examples are: e-skin, e-paper, e-nose, smart-fabrics, flexible displays, printed electronics or radio frequency identification tags (RFID). OTFTs form the basis of future organic electronic circuits.

The model is implemented in Simucad SmartSpice, a leading analog circuit simulator.

The UOTFT SPICE model combines universal charge-based field effect transistor modeling with OTFT specific channel charge, mobility bias, temperature dependences, and nonlinear contact resistances. This combination maximizes UOTFT generic modeling capabilities, and makes it suitable for a large variety of OTFT device architectures, material specifications, and fabrication technologies.

The design of organic electronics circuits depends on accurate and efficient OTFT compact models in commercial circuit simulation tools. A range of distinct features in OTFT device properties require special consideration and a different modeling approach compared to their inorganic counterparts. The most notable differences include a trap-assisted charge distribution and mobility behaviour, unipolar or bipolar charge accumulation operation mode and non-ohmic contact resistances. The existing MOSFET, as well as amorphous and poly-silicon TFT models, are therefore not suitable for the design of OTFT circuits.

David Fyfe, CEO of CDT stated “This activity will enable CDT to further develop its technology base in these new areas of organic semiconductor technology. We are delighted to be working with Silvaco on this project which will speed development and commercialisation of low cost rigid and flexible electronics applications of organic semiconductor technology”.

The project is being part-funded by the UK government’s Technology Strategy Board and their Technologist for Electrical Systems, Mike Biddle commented: “We are very happy with the excellent progress made by this project, and to see that this new approach will soon be ready for commercial exploitation. This is a great example of world class businesses coming together in the UK to research and develop innovative technology that has global market potential.”

“We are delighted to be working with a leading organic research company such as CDT, and the UK government, on such a cutting edge project,” said Dr Ivan Pesic, President and CEO of Simucad. “This new ground-breaking model will enable circuit designers to accurately simulate the next generation of organic circuits. We look forward to continuing this partnership on future projects.”

“CDT continues to focus its effort on supporting the P-OLED supply chain and is pleased to be involved in yet another joint development project which has the potential of bringing new materials and improved device performance to our licensees”, says David Fyfe, CEO of CDT.

“We are excited about the prospect of including new materials and device structures arising from a successful JDA between CDT and Novaled in our product plans. Having the support from CDT and Novaled, leading companies in their fields, increases the potential range of new products we can offer to the market”, says Kazuhiko Miyata, General Manager of Sumitomo New Business Development office.

“Novaled, with its Novaled PIN OLED™ technology, is a leader in high efficiency OLED devices and a recognized supplier of specialised dopants and organic transport materials”, says Gildas Sorin, CEO of Novaled. “We are pleased to contribute to the development of P-OLED devices and look forward to a successful collaboration with both CDT and Sumitomo Chemical. This co-development agreement is consistent with our strategy to promote our dopants in all organic electronic fields.”

Process technology, including device design, equipment specifications, and fabrication know-how, will be transferred to Ehime from Cambridge Display Technology (CDT), UK. Sumitomo and CDT will further refine and demonstrate process capabilities at the pilot line in Ehime.

Sumitomo Chemical began working on P-OLED technology in 1989. In 2001, Sumitomo Chemical and CDT Ltd. of Cambridge, England, entered into a technical assistance agreement, including technology licensing for light-emitting materials, and in September, 2007 Sumitomo Chemical acquired CDT Ltd. to ensure and accelerate the commercialisation of P-OLEDs. Sumitomo and CDT also previously formed a joint venture – Sumation – to develop and commercialise the P-OLED materials.

The investment in a manufacturing process development line will bring together process technology from CDT, latest light emitting polymer materials from Sumation, and engineering and manufacturing know-how from Sumitomo’s colour filter and IT-related materials business to demonstrate the full potential of P-OLED technology in terms of display resolution, substrate scaleability, and manufacturing cost and yield.

K. Nakae, Sumitomo’s Executive Officer responsible for Corporate Planning, said “We are convinced that solution-processable polymer-based technology is the preferred approach for the fabrication of high resolution OLED displays. We have seen the excellent progress made at CDT and have decided to invest in an integrated line at Ehime to take the manufacturing and process technology to the next level.”