NHK and Japan Catalyst have developed OLED components that are much more resistant to oxygen and moisture in the air than previous prototypes. The technology developed this time shows that it can be greatly improved by simply changing the internal structure and materials of the components. Durability.
From the published content, if the previous prototype is exposed to the air, as the cathode is continuously oxidized, the light-emitting area will be reduced to 1/2 after 100 days, and the components of this time are hardly deteriorated. In this case, the cost of the sealing material used outside the component may be lowered.
The OLED elements developed by NHK and Japan Catalyst adopt an "inversed OLED" (iOLED) structure, which is opposite to the inter-electrode element structure of the bottom-emitting type element. Specifically, an electron injecting layer, an electron transporting layer, a light emitting layer, a hole transporting layer, and an anode (titanium, gold, or the like) are sequentially formed on a transparent substrate/transparent cathode (ITO). In general, a bottom-emitting OLED device is formed by forming a hole transport layer (PEDOT: PSS, etc.), a light-emitting layer, an electron transport layer, and an electron injection layer on a transparent substrate such as glass/transparent anode (ITO or the like). A cathode (aluminum or the like) is formed.
To this end, NHK and Nippon Shoku decided to use other materials in the electron injection layer. However, most other materials are "sputtered" using a high-energy manufacturing process, which destroys the already formed electron transport layer and luminescent layer. Therefore, the two companies chose an iOLED structure that can form an electron injection layer before forming an electron transport layer.
However, for the electron injecting layer material that replaces LiF, NHK only discloses "materials that are not easily oxidized and have high integration with ITO in terms of work function". Prior to this, OLED development rarely used iOLED construction, precisely because of the poor integration of the two, "it is difficult to use ITO as a cathode."
In terms of durability comparison, the two sides conducted experiments in which the following three components were placed in a normal temperature air environment for comparison. The three components are: (1) a light-emitting side using a glass substrate, a back surface sealed with a common resin-based material, and a component having a normal bottom-emitting structure; (2) the same sealing method, using an iOLED structure, an electron injecting layer material A (3) The same sealing method, using the iOLED structure, the component of the electron injection layer material B.
As a result, it was revealed that (1) a non-luminous dark spot representing deterioration was apparently started after 20 days, and after 100 days, 1/2 of the light-emitting portion had deteriorated. (2) Deterioration began to become apparent after 40 days. And (3) no deterioration was found after more than 100 days.
According to the above results, the use of the iOLED structure like the element (2) does not sufficiently improve the durability, and in addition to the iOLED structure, the selection of the material of the electron injection layer is also an important condition for improving the durability.
From the published content, if the previous prototype is exposed to the air, as the cathode is continuously oxidized, the light-emitting area will be reduced to 1/2 after 100 days, and the components of this time are hardly deteriorated. In this case, the cost of the sealing material used outside the component may be lowered.
The OLED elements developed by NHK and Japan Catalyst adopt an "inversed OLED" (iOLED) structure, which is opposite to the inter-electrode element structure of the bottom-emitting type element. Specifically, an electron injecting layer, an electron transporting layer, a light emitting layer, a hole transporting layer, and an anode (titanium, gold, or the like) are sequentially formed on a transparent substrate/transparent cathode (ITO). In general, a bottom-emitting OLED device is formed by forming a hole transport layer (PEDOT: PSS, etc.), a light-emitting layer, an electron transport layer, and an electron injection layer on a transparent substrate such as glass/transparent anode (ITO or the like). A cathode (aluminum or the like) is formed.
To this end, NHK and Nippon Shoku decided to use other materials in the electron injection layer. However, most other materials are "sputtered" using a high-energy manufacturing process, which destroys the already formed electron transport layer and luminescent layer. Therefore, the two companies chose an iOLED structure that can form an electron injection layer before forming an electron transport layer.
However, for the electron injecting layer material that replaces LiF, NHK only discloses "materials that are not easily oxidized and have high integration with ITO in terms of work function". Prior to this, OLED development rarely used iOLED construction, precisely because of the poor integration of the two, "it is difficult to use ITO as a cathode."
In terms of durability comparison, the two sides conducted experiments in which the following three components were placed in a normal temperature air environment for comparison. The three components are: (1) a light-emitting side using a glass substrate, a back surface sealed with a common resin-based material, and a component having a normal bottom-emitting structure; (2) the same sealing method, using an iOLED structure, an electron injecting layer material A (3) The same sealing method, using the iOLED structure, the component of the electron injection layer material B.
As a result, it was revealed that (1) a non-luminous dark spot representing deterioration was apparently started after 20 days, and after 100 days, 1/2 of the light-emitting portion had deteriorated. (2) Deterioration began to become apparent after 40 days. And (3) no deterioration was found after more than 100 days.
According to the above results, the use of the iOLED structure like the element (2) does not sufficiently improve the durability, and in addition to the iOLED structure, the selection of the material of the electron injection layer is also an important condition for improving the durability.
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