New method to measure OLED molecule behavior while device is working.
Last week the National Institute of Advanced Industrial Science and Technology (AIST) presented at the IDTechEx, Asia 2012 event. AIST have developed a method that can selectively measure the behavior of specific molecules at the interfaces of organicas layers in a multilayered organic light emitting diode (OLED) device during light emission in collaboration with Chemical Materials Evaluation and Research Base (CEREBA). The researchers have succeeded for the first time in measuring the behavior of the electric charges in a device at the molecular level.
The method uses an advanced laser spectroscopic technique that has been improved to measure the molecular vibrational spectrum at the interface of a specific organic layer inside an OLED device. By employing a signal enhancement phenomenon that occurs at the interface with a concentrated electric field, the method can be used to evaluate the molecular condition of the organic layer during light emission without destroying the device.
The method is expected to be useful for elucidating the deterioration of materials and deterioration of interfaces in a device on the basis of molecular level information. Such elucidation is necessary for extending the life of OLED devices.
Conceptual diagram of laser spectroscopy of a multilayeredOLED device during light emission
OLED devices are composed of stacked organic layers with different properties sandwiched between two electrodes. The device emits light when a voltage is applied to the electrodes. In ordinary multilayered OLED devices, between three and fiveorganic layers are stacked on a transparent electrode with an overall thickness of only about 200 nm. To eliminate the influence of oxygen and water, the device is tightly sealed with a desiccant (Fig. 1). The multilayered OLED device used for the measurement was composed of six different organic substances and had a brightness half-life (the length of time required for the brightness to deteriorate to 50% of the initial value) of more than 13,000 hours at brightness of 1000 cd/m2 (candelas per square meter).
In this effect, the wavelength of the visible light is adjusted to match the absorption wavelength (color) of the target organic substance, thus allowing only the target organic substance to be selectively brought to a high-energy state. The use of this double resonance effect makes it possible to eliminate the influence of other organic layers within the device and to enhance and isolate the signals from the target organic layer. In addition, to minimize damage that could be caused to the device by the laser light, improvements were made to the SFG spectrometer so that it could maintain its measurement resolution even when the laser power was reduced to less than 1/100 of that in conventional SFG spectrometers.
Figure shows the structure of an actual multilayered OLED device. The visible and infrared laser lights used in SFG spectroscopy were incident from the transparent substrate side when measurements were made. Even though an operating OLED device emits strong light, the SFG light has a different wavelength from the emitted light. Moreover, because the beam-like SFG light is emitted in a certain direction, a filter and two spectrometers were used to clearly separate the SFG light from the strong emitted light and then measure it.
For OLED devices to be applied to next-generation flat screen televisions, smartphones, and flexible devices, the degradation progressing in practical devices must be investigated in detail. Using the developed method, the researchers plan to continue to investigate the molecular-level status in operating OLED devices and in devices that have been in operation for long hours. They aim at the molecular-level elucidation of the driving mechanism of OLED devices and the degradation mechanism of them which is indispensable to the extension of device life.
The researchers also aim to apply the method to the evaluation and analysis of other organic electronic devices such as organicsolar cells and organic transistors.
Reference:
No hay comentarios:
Publicar un comentario