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>> Technology to reduce the energy consumption of OLED displays will be available 30th,July,2019
According to foreign media reports, an international research team led by Kensuke Kimura, a scientist at the Japan Institute of Physical Chemistry (RIKEN) Surface and Interface Science Laboratory, is developing a technology that can reduce the energy consumption of OLED displays.
A recent article by the research team entitled "Formation of Selective Triplet Excitons in Single Molecules" was published in the journal Nature. For the technology, the following background needs to be understood.
Current through the OLED material causes the formation of excitons, while excitons are pairs of electrons and holes. More precisely, the current injected into the OLED material forms spin-single-state excitons (with opposite spins) and spin-triplet excitons (with spins in the same direction) at a ratio of 1 to 3. ). The singlet state is a higher energy state and can be converted to a triplet state. When a singlet or triplet transitions to a lower energy state, light is produced.
Phosphorescence (phenomenon) in current generation OLED materials is usually based on triplet decay. Based on this fact, the use of energy to produce higher energy singlet states is not efficient. A material/process that only produces a triplet state and emits light by triplet decay should have a lower OLED operating voltage, thus enabling improved energy efficiency of the overall OLED display. However, until now, no effective method has been developed to enhance the direct formation of triplet states. Therefore, the research carried out by the research team aims to solve this problem.
The team's recent research aims to understand the basic physical principles behind exciton generation. To this end, the team prepared a model system based on organic semiconductors called 3,4,9,10-tetracarboxylic dianhydride (PTCDA). The semiconductor is adsorbed on an ultrathin insulating film composed of three single layers of NaCl, and the single layer of NaCl is supported by a metal film composed of Ag (111). It should be noted here that (111) refers to the crystal structure of silver. They give the molecule a negative charge by a specific method. In the next step, a current from a scanning tunneling microscope (STM) can induce luminescence of the molecule. The type of exciton produced by this process is determined by an optical detection system that analyzes the emission spectrum.
Both phosphorescent and fluorescent signals appear when a high voltage is applied. However, when a low voltage is applied, only phosphorescence (phenomenon) occurs. These results indicate that the selective formation process of triplet excitons does not produce singlet excitons. Theoretical calculations confirmed the experimental results and verified their mechanism.
The (a) part of the figure below shows the configuration of the measurement; the part (b) is the scanning tunneling microscope image of the PTCDA adsorbed on NaCl grown on Ag(111); the part (c) is produced by the material. Luminescence spectrum.
Technology to reduce the energy consumption of OLED displays will be available
In describing their test results, the team said: "We believe that we are able to do this mainly because of previously unknown mechanisms in which electrons can be selectively shifted from charged molecules according to their spin state. In addition, we have subsequently demonstrated a new method of manipulating excitons that is critical for electron transport within OLEDs. It can be controlled by the manipulation of exciton formation in the OLED by manipulating electron spins inside the molecule. Electronic transmission process."
In their research paper, they said that it is expected to "design an OLED with a lower operating voltage that allows for the exchange of interactions."
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