| Summary: | 碩士 === 國立嘉義大學 === 電子物理學系光電暨固態電子研究所 === 101 === The efficient single-layer hybrid organic light-emitting diodes ( OLEDs ) with p–i–n homojunction are investigated. The OLEDs are only based on the conventional emitting/electron-transporting material tris-(8- hydroxyquinoline) aluminum (Alq3), which is p- and n-type doped with molybdenum trioxide ( MoO3 ) and cesium carbonate ( Cs2CO3 ) adjacent to the electrodes. By electrical doping, the carrier injection and transporting characteristics are greatly improved, leading to the reduced turn-on voltage and enhanced luminous efficiency of the p-i-n device. By using the various measurements and analysis, including the X-ray and ultraviolet photoelectron spectroscopy ( XPS and UPS ), absorption spectra, space-charge-limited current ( SCLC ) measurements, capacitance spectroscopy, and capacitance-voltage ( C-V ) measurements, such improved properties are attributed to the reasons below. (I) The formation of the charge transfer complex produced by doping p- or n-type dopants into Alq3, which provides much more free carriers and causes the lowered injection barrier. (II) Carriers will move toward the center energy levels of this distribution due to the partial filling of the density-of-states (DOS) distribution upon doping, and then results in the increased carrier mobility. (III) The charge balancing of electron and hole improved by doping MoO3 into Alq3 and confining the recombination zone to the intrinsic-Alq3 layer. As compared with the non-doped ( i-i-i ) or single-doped ( p-i-i/i-i-n ) OLEDs, the p-i-n OLEDs show the best performances such as the lower turn-on voltage of 4.3 V ( at 1 cd/m2 ), the higher maximum luminance of 5860 cd/m2 ( at 11.4 V ), the higher luminous efficiency of 2.54 cd/A ( at 100 mA/cm2 ), and the longer operating time of 700 min., which are even better than the two-layer ( NPB/Alq3 ) heterojunction OLEDs using the same emitting layer.
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