有機EL素子における電気伝導の温度特性とキャリア挙動

摘要

Organic Electroluminescent device (OLED) was fabricated using a vacuum evaporation method and thermal properties were investigated. The OLED has an Indium Tin Oxide (ITO)/ N,N'-diphenyl-N,N'-bis(3-methylphenyl) 1- 1'biphenyl- 4,4'-diamine (TPD)/ tris- (8-hydroxyquinoline) aluminum (Alq)/ Lithium fluoride (LiF)/ aluminum (Al) structure. An electron dominant device of an Al/ Alq/ LiF/ Al structure, or a hole dominant device of an ITO/ TPD/ Al structure was also fabricated in order to study the carrier behavior in the OLEDs. The current density vs. voltage (J-V) properties with various thickness of organic layers were investigated in the both electron and hole dominant devices, and the thermal dependence of J-V properties was observed in the devices. At room temperature, conductions in large current region were considered to be due to space"charge"limited current for all the devices. Especially, for the Al/ Alq/ LiF/ Al device and the OLED, J∝V~(m+1) relationships were observed across wide current region. At low temperature, tunnel currents were estimated for the ITO/TPD/A1 device. For the Al/ Alq/ LiF/ Al device and the OLED, J∝V~(m+1) relationships were observed across wide current region at low temperature.%有機電界発光（EL）素子は1997年に初めて製品化され て以来様々な研究機関で盛んに検討され，今日までに家電 製品，モバイル端末さらには車載用オーディオ，計器など のデジタルディスプレイとして数多く採用されている。デ ィスプレイの仕様もモノカラー（緑，青），エリアカラー， マルチカラーが開発され，さらに近年では白色モノカラー， フルカラーと着実に進化を続けている。またこれに伴い有 機EL素子の性能も有機材料や成膜プロセスの改良，封止技 術の開発などにより，コダック社による2層型有機EL素子 の発表から20年足らずの間に飛躍的に向上した。