PNNL

Abstract

Organic light emitting device (OLEDs) may provide a low-cost, long-lived, and efficient wide area lighting solution if a number of challenges in reliability, cost and efficiency can be overcome. There is a need to develop new TCOs for use as the anode in a bottom-emitting device that do not contain In, have optimal work function, conductivity and visible light transmission properties, possess acceptable stability and possess a high work function to match the deep HOMO of blue OLED HTLs. We report here results from our efforts to scale up sputter deposition on large area substrates (up to 12”x12”) of TCO candidates (including Ga:ZnO and Zn:SnO) identified using combinatorial methods. We present transmission, electrical properties, work function, compositional and structural data for these films. Finally, we have evaluated the use of these materials in OLEDs, and show device performance comparisons between devices fabricated on combinatorial substrates, single composition substrates, and substrates grown at larger scale (up to 12”x12”). Post-operation analysis of the materials using a combination of surface analysis and electron microscopy techniques was performed. The device results demonstrate that we are able to generate substrates with the appropriate work function to reduce the operating voltage of blue phosphorescent OLEDs compared to commercial ITO, which we ascribe to improved work function-HOMO energy matching leading to more efficient charge injection into the device HTL.