1. Field of the Invention
The present invention relates to an organic light emitting device.
2. Description of the Related Art
An organic light emitting device is an electronic device including a pair of electrodes formed of an anode and a cathode, and organic compound layers placed between the pair of electrodes. When a voltage is applied to the pair of electrodes, a hole and an electron supplied from the electrodes recombine in an emitting layer in the organic compound layers to produce an exciton, and the organic light emitting device outputs light upon return of the exciton to its ground state.
The organic light emitting device has been attracting attention as one next-generation full-color display technology because the device has such characteristics as high-speed responsiveness, high luminous efficiency, and flexibility. Accordingly, material technology development and device technology development have been vigorously performed.
In particular, high durability against the deterioration of the organic light emitting device due to its continuous driving has been required for applying the organic light emitting device to a full-color display or the like, and hence development with a view toward the improvement of the durability has been progressed.
Japanese Patent Application Laid-Open No. 2003-077676 discloses an organic light emitting device whose durability has been improved by doping a hole transport layer constituting the organic light emitting device with rubrene, 9,10-diphenylanthracene (DPA), or an oxadiazole compound (such as OXD8).
The deterioration of the organic light emitting device is considered to be due to the action of high-energy chemical species present in the organic light emitting device (such as a hole and an electron injected from the electrodes, and an exciton produced in the organic compound layers). However, a detailed mechanism of the deterioration has not been elucidated yet.
By the way, in Japanese Patent Application Laid-Open No. 2003-077676, an attempt has been made to lengthen the lifetime of the device by doping a layer forming an emission interface where excitons are present at a high density with a specific compound, but a practically sufficient lifetime has not been obtained.