Light-Emitting Element, Light-Emitting Device, Lighting Device, and Electronic Appliance

摘要

An inverted-structure light-emitting element is provided. One embodiment of the invention disclosed in this specification is a light-emitting element including a cathode, a layer serving as a buffer over the cathode, an electron-injection layer over the layer serving as a buffer, a light-emitting layer over the electron-injection layer, and an anode over the light-emitting layer. The electron-injection layer includes an alkali metal or an alkaline earth metal. The layer serving as a buffer includes an electron-transport material. In the inverted-structure light-emitting element, contact of the alkali metal or alkaline earth metal included in a material of the electron-injection layer with the already formed cathode increases the driving voltage of an EL element and reduces emission efficiency. This problem becomes prominent particularly when the cathode includes an oxide conductive film. To prevent this, the layer serving as a buffer is provided between the cathode and the electron-injection layer.

主权项

1. A light-emitting element comprising:
an anode; a cathode; a light-emitting layer between the anode and the cathode; a first layer between the cathode and the light-emitting layer; and a second layer between the first layer and the light-emitting layer, wherein the second layer includes an alkali metal or an alkaline earth metal, and wherein the first layer includes an electron-transport material.