BMBF Project NEMO: Research on new OLED materials successfully completed under the leadership of Merck

After three years of intensive research in the field of new, soluble processable materials for OLEDs (Organic Light Emitting Diodes), Merck, together with ten other partners from industry and universities, successfully completed the project "New Materials for OLEDs from Solution" (NEMO), funded by the Federal Ministry of Education and Research (BMBF). The newly developed materials can now be integrated into large-area OLED components for, e.g., televisions, illuminated displays, and lighting for objects or rooms. They are especially suitable for printing processes, which, due to their high material utilization compared to conventional manufacturing processes with evaporation materials, allow for more cost-effective production of OLEDs. The total budget of the project was €29 million. Merck led the consortium of eleven partners.

In this project, Merck developed and tested new phosphorescent materials for red, green, and blue applications. For example, the extrapolated lifetime at 50% of initial brightness (= durability in operation) of green triplet emitter materials was increased from 10,000 hours to over 200,000 hours, while simultaneously increasing the efficiency of these materials from 30 cd/A to over 70 cd/A (Candela/Ampere) at a brightness of 1000 cd/m².

"The project success is a major and important step for printable material systems with very good performance data," says Dr. Udo Heider, who heads the OLED business field at Merck. "This enables our customers to implement cost-efficient manufacturing processes that, due to low material losses in production, ultimately also benefit the environment."

The scope of the project ranged from light-emitting materials processed from a solution, through charge transport materials, to new adhesives for reliable encapsulation of each OLED component. Additionally, physical investigations on the materials and OLED components were conducted, providing an expanded understanding for future material development.

Besides Merck, the following companies and institutes participated in the project: Humboldt University of Berlin, Delo Industry Adhesives, Enthone GmbH, Fraunhofer Institute for Applied Polymer Research IAP, Heraeus Precious Metals GmbH & Co. KG, University of Potsdam, University of Regensburg, and University of Tübingen.

Humboldt University of Berlin
At Humboldt University of Berlin, novel electron transport materials were produced and tested using modular synthesis strategies.

DELO Industry Adhesives
The company focused on developing adhesives with low water vapor permeation for planar encapsulation. A key aspect of the work was optimizing the compatibility of the adhesive with OLED materials. Suitable adhesive systems were identified, and a significant reduction in defective areas in the component was achieved. The developed systems were comprehensively characterized.

Enthone GmbH (formerly Ormecon)
At the Enthone Nano Science Centre in Ammersbek, dispersions of the electrically conductive polymer polyaniline were developed, from which charge carrier layers for OLEDs were produced. Such displays showed electrical properties comparable to those with the previously used material.
For OLED component characterization, the OLEDs prepared by Merck were examined using impedance spectroscopy. Unstable regions responsible for the short lifetimes of OLEDs were identified. Furthermore, predictions about lifespan could be made from impedance measurements on briefly stressed displays.

Fraunhofer Institute for Applied Polymer Research IAP
The Fraunhofer Institute for Applied Polymer Research in Potsdam (IAP) developed polymer-based phosphorescent systems for green and red Merck emitters. Suitable charge transport molecules were attached as side groups to a polymer main chain, and it was demonstrated that this leads to comparable or even improved performance parameters and lifetimes of OLEDs compared to solution-processable small molecules. For "green," current efficiencies of 61 cd/A and lifetimes of 66,000 hours at 1000 cd/m² were achieved.

Heraeus Precious Metals GmbH & Co. KG (formerly H.C. Starck Clevios GmbH)
The company developed new materials for interlayers that improve the injection of charge carriers from the anode into the OLED emissive layer and contribute to increasing device lifespan. The work function of hole injection layers can now be precisely adjusted within a range of 4.8 – 6.1 eV. Water-soluble polymer counterions were developed, enabling the first realization of water-free PEDOT materials. Simultaneously, work was done on transparent electrodes that can be deposited from solution and help reduce costs for OLEDs. The conductivity of PEDOT:PSS films was further increased. First ITO-free OLED lamps were realized. By combining with screen-printed silver lines, OLED surface lamps without noticeable luminance drop from the edge to the center of the device were enabled.

University of Potsdam
Researchers at the University of Potsdam investigated physical properties such as charge carrier transport and excitation dynamics in newly synthesized materials and in the finished device. In combination with steady-state and transient simulations, insights were gained into which processes limit the efficiency of the LEDs and which determine the aging of the devices.

University of Regensburg (represented by two chairs)
In Professor Yersin's group, new emitter classes with strong and weak metal-metal interactions were developed, showing the singlet harvesting effect discovered in Regensburg. This makes it possible to realize highly efficient emitters for OLEDs based on very inexpensive copper complexes. These studies on singlet harvesting with newly developed copper complex emitters were awarded an innovation prize at the international "SPIE Organic Photonics" conference in Brussels in April 2012.
Furthermore, in Professor König's group, emitter libraries were synthesized using a simple, combinatorial protocol. A screening system was developed for rapid and nearly automated identification and characterization of individual emitters, as well as for their photostability testing. This allowed the investigation of degradation behavior of many substances and the drawing of conclusions about various degradation mechanisms.

University of Tübingen (represented by two chairs)
The Tübingen groups provided new organometallic complex compounds that can be used as luminescent molecules in OLEDs. Coordination compounds of rhodium, iridium, palladium, platinum, copper, silver, and gold were synthesized, characterized, and new promising conduction structures for emitter materials were developed.
Press releases from Merck KGaA are sent simultaneously with publication on the internet via email. Use the web address http://www.newsabo.merck.de to register online, change your selection, or cancel the service.