Improved Organic Light Emitting Diodes Using Cryogenic LiF/Al Deposition

Abstract

The effect of cryogenic temperature deposition of Al and LiF contacts on the electrical and optical performance of organic light emitting diodes (OLEDs) was investigated. The reverse current of OLED with 77 K deposited contacts was reduced by one order of magnitude, and the output light intensity was dramatically improved compared to the device with conventional e-beam evaporated cathodes, due to the reduced damage on the metal contacts and the organic film interface. Atomic force microscope (AFM) imaging showed uniformly distributed smaller grains, and the X-ray diffraction (XRD) pattern indicated better crystallinity for the 77 K deposited metal film. Also, an abrupt interface between metal contact and polymer was observed from secondary ion mass spectroscopy (SIMS) depth profiling. (C) 2012 The Japan Society of Applied Physics