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2008
Conference Paper
Titel
Al top cathode deposition on OLED using DC magnetron sputtering
Abstract
We study the sputter deposition on top of organic layers to form a cathode electrode. Since most organic materials are sensitive to the high energetic particles like neutralized ions and ultraviolet (UV) photons generated in glow discharge, sputtering can deteriorate the performance of organic light emitting diodes (OLED). A p-i-n type orange OLED based on doped charge transport layers and emitting layer consisting of alpha-NPD(4,4-bis [N-(1-naphtyl)-N-phenyl-amino- ]biphenyl) and Iridium(III)bis(2-methyldibenzo-[f,h]quinoxaline)(acetylacetonate) is realized, having low operating voltage and high efficiency. The organic layers are vacuum-evaporated on ITO coated glass substrates in a vertical inline deposition tool, and aluminium is deposited on the organic layers by direct current (DC) magnetron sputtering to form a cathode. Various sputter process parameters are selected and applied to form the cathode. Ytterbium was evaporated on the organic layers by the metal evaporation in order to set a reference device. The fabricated OLEDs are characterized by means of I-V-L characteristics and lifetime measurements. The results are explained by sputter parameters in order to identify the effect of Ar neutrals. The OLED having sputtered Al cathode show a driving voltage of 4.2 V, a power efficiency of 7.7 lm/W, and a current efficiency of 10.6 cd/A at 1000 cd/m2 comparable to the OLED having the evaporated cathode. However, with the OLEDs having the sputtered cathodes exhibit shorter lifetime than OLED that have the Yb cathode deposited by evaporation due to the higher leakage currents.