Light-emitting diodes with hetero-PN-junction

This invention relates to a light-emitting device provided with a light-emitting layer structure by utilizing electroluminescence of a light-emitting material which emits light by passing an electric current therethrough under an applied electric field and which is formed in a layered structure, and, in particular, it relates to an organic light-emitting diode in which the light-emitting layer structure is constructed from a hetero-PN-junction comprising an organic semiconductor as a light-emitting zone. An organic light-emitting diode with high luminance and high efficiency comprising an anode, an organic pn-junction and a cathode layered sequentially in this order, wherein the organic pn-junction emits light by an electric current passing through the diode in an electric field applied between the anode and the cathode, characterized in that the organic pn-junction is composed of an organic p-type luminescent-semiconductor thin film and an organic n-type luminescent-semiconductor thin film, wherein one surface of the organic p-type luminescent-semiconductor thin film is in contact with the anode and another surface of the organic p-type luminescent-semiconductor thin film is in contact with the organic n-type luminescent-semiconductor thin film, and one surface of the organic n-type luminescent-semiconductor thin film is in contact with the cathode and another surface of the organic n-type luminescent-semiconductor thin film is in contact with the organic p-type luminescent-semiconductor thin film and wherein the diode satisfies all the conditions of the following equations 1 to 3:in which Xdenotes an absolute value of the electron affinity of the organic p-type luminescent-semiconductor, Xdenotes an absolute value of the electron affinity of the organic n-luminescent-semiconductor, IPdenotes an ionization potential of the organic p-type luminescent-semiconductor and IPdenotes an ionization potential of the organic n-type luminescent-semiconductor.