RT-stable Electride and Its Application to Cold Electron Emitter and Electron Injection Layer in OLED

摘要

Electrides are ionic crystals in which electrons work as anion. However, the fatal drawback of electrides reported so far was extremely poor thermal instability, i. e. , it decomposed at -40°C for the best material, In 2003, we fabricated roomtemperature stable electride by chemical treatment of nano-porous crystal 12CaO·7Al2O3(C12A7) with Ca metal[1].C12A7, a refractory oxide (melting point 1 420°C), has a cubic lattice and a chemical formula of 2 per unit cell. The crystal is composed of sub-nanometer-sized cages which are connected 3-dimensionally by sharing open mouse. The unit cell has 2 chemical formula and may be described as[ Ca24 Al28 O64 ]4 + +2O2- , where the former and the latter denote the chemical formula of cage walls and free oxygen ions, respectively. Two free oxygen ions are randomly distributed in the cages to compensate positive charged of the walls. We synthesized{[Ca24 Al28 O64]4+ (4e- ) }, a first RT-stable electride , by substituting a Free oxygen ions with 2 electrons.The resulting materials exhibit a high electrical conductivity of 1,500Scm-1 at 300 K. The work function, evaluated from electron field emission measurements is ～0.5 eV[2a], which is extremely small among electron emission materials resorted so far. This material works well as a thermal field-electron emitter at ～900°C[2b], which is much lower than that ( ＞1 600°C) of LaB6.The value of work function measured by UPS on fresh surfaces in UHV was 2.4 eV, which is comparable or smaller than that of an alkali metals, irrespective of high stability to atmospheric conditions. Thus, we examined this materials as the electron-injection material of OLED, finding that the barrier height of electron injection of the electride/Alq3 is ～0.6eV, which is less than half of that ( ～1.4eV) of Al/Alq3.