Horst Vestweber

White and blue temperature stable and efficient OLEDs using amorphous spiro transport and spiro emitting compounds

The temperature stability of white and blue OLEDs was investigated by observing the I-V, EL-V and the spectral characteristics of various devices stored at elevated temperature (up to 130 degrees Celsius). Blue multilayer organic light emitting diodes (OLEDs) containing PEDT (polyethylenedioxythiophene) or PANI (polyaniline) derivatives as the hole injection and puffer layer, aromatic diamines like Spiro-TAD (2,2,7,7- tetrakis(diphenylamino)spiro-9,9-bifluorene) as a hole transport material (HTM), Spiro-DPVBi (2,2,7,7- tetrakis(2,2-diphenylvinyl)spiro-9,9-bifluorene) as an emitting material (EM) and of Alq3 (tris(8-hydroxy- quinoline)aluminum) as the electron-injection and electron- transport layer (ETL) were fabricated. White OLEDs were prepared, containing an additional DCM (dicyanmethylene-2- methyl-6-(p-dimethylaminostyryl)-4H-pyran) doped Alq3 layer between the Spiro-DPVBi and Alq3 layer. Use of Spiro-TAD as a hole transport material (HTM) and of Spiro- DPVBi as an emitting material (EM) resulted in dramatically improved temperature stability: for the white and blue OLED no significant deterioration up to 130 degrees Celsius were found. Devices consisting of non spiro components like NPB and/or DPVBi already started to degrade at much lower temperatures.

Developments in polymer materials for electroluminescence

In the last few years industrial research into materials fulfilling the needs of the fledgling OLED display industry have intensified considerably. At Covion we have developed a range of polymers based on phenyl-PPV derivatives which are now being commercially exploited in the first polymer LED applications. These materials have been developed systematically with the demanding requirements of the devices (e.g., high efficiency and lifetime) and the industrial applicability (e.g. processibility, reproducibility and reliability of supply) in mind. However due to market forces, such as the introduction of 3rd generation mobile communication technology, there will be an immediate demand for materials for full color OLED displays. In this paper we will report on progress in the development of Red, Green and Blue (RGB) materials at Covion. The requirements for the different colors vary depending on band gap (amongst others) and therefore the challenges for each color are different. The experience gained in understanding the important structure-property relationships in the phenyl-PPVs has been used to develop these new RGB materials.

51.1: Invited Paper: Polymers for Efficient OLEDs

Polymer light-emitting diodes (PLEDs) and displays based on polymer technology have made dramatic progress during the last years. In particular, efficiency and device lifetime have improved to such a significant extent that first products will commercialized within this year. We report here on the technical status of materials and devices upon which this success is based. Efficiency and especially operational stability are now at a level which easily meets the requirements for a variety of applications, namely power efficiencies are well above 10 lm/W, operational lifetimes are exceeding 20000 hours at display brightness levels and room temperature). This progress has been achieved by the careful analysis of failure mechanisms and the systematic improvement of materials. The first products, i. e. back-lights (for LCD-displays), segmented displays, and finally passive-matrix-addressed low-information-content (LIC) graphical displays are described. Light emitting polymerss are now manufactured on industrial scale under high purity conditions; filling and packaging is done under a class 10 clean room condition. For details see H. Becker Paper 46.1.