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Japanese Researchers Study New Methods To Improve OLED Efficiency And Strength

Sep 21, 2018

Recently, researchers at the Center for Organic Photonics and electronic research at Kyushu University in Japan showed a new way to improve the efficiency of OLEDs by splitting the energy of one exciton into two parts using single-state fission, which could limit the production efficiency of OLED exciton by more than 100%. The exciton is the energy bundle in the OLED, which is formed by a positive charge on the molecule and a negatively charged connection. A exciton can produce a photon by releasing energy.

There are two forms of exciton, namely, single State and triple state. The researchers at the Center for Organic Photonics and electronics at Kyushu University, Japan, use molecules that can accept triple Exciton, where the energy of the triplet exciton is half the energy of a single-state exciton, overcoming the limitation that each pair of charges can only form one exciton. A single exciton can transfer half of its energy to neighboring molecules while preserving half of its energy.

This single-state fission process can cause a single-state exciton to produce two triple-state exciton, and then transfer the triplet-Exciton to the second class of molecules that can use energy to emit near-infrared (NIR) light. Professor Hajime Nakanotani said: "In short, we use molecules as transformation machines for the exciton in OLED." A conversion machine similar to converting a $10 bill into two 5-dollar bills that converts an expensive high-energy vibrator into two half-price low-energy exciton.

The researchers evaluated the efficiency of a single-state fission process by comparing the NIR emission with the tiny visible light emission from the remaining single-state exciton exposed to various magnetic fields. Through experiments, the researchers confirmed that the single-state fission produced by the triple State in the Exciton energy from the Dark triplet state transfer after the emission of Nir Electroluminescent, total exciton production efficiency of 100.8%.

The researchers say their research is the first to use single-state fission to improve the efficiency of OLEDs, although the single-state fission was previously used in organic solar cells. The team said the overall efficiency of using single-state fission is still relatively low, as the organic emitter's near-infrared emission tradition is inefficient. Nonetheless, this new approach provides a way to improve the efficiency and strength of the OLED without altering the emitter molecule.

To further improve efficiency, researchers are looking at ways to improve the molecular body of the emitter itself. With further improvements, the team hopes to increase the efficiency of the exciton to 125%, which is the next limitation for researchers, since electrical operations naturally produce 25% of single-state exciton and 75% Triple-state exciton.

Once the team achieved this goal, the team began to study how to convert the triplet exciton to a single-state exciton to achieve 200% quantum efficiency. "Near-infrared light plays a key role in biology, medical applications, and communication technologies," said Chihaya Adachi, director of opera. Now that we understand that single-state fission can be used in OLEDs, there is a new way to overcome the challenges of producing highly efficient near-infrared OLED, and it will soon be practical to use.

The experiments show that even under electric excitation, the triple-state exciton produced by single-state fission may also be used as electroluminescence, thus improving the quantum efficiency of OLED. Electroluminescence using single-state fission can provide a way to develop high-intensity NIR light sources, which is particularly important in sensing, optical communications, and medical applications.