OLED compatible water-based nanolaminate encapsulation systems using ozone based starting layer

Highly efficient nanolaminate diffusion barriers made of TiO2/Al2O3 multilayers using low temperature atomic layer deposition optimized for organic light emitting diodes are presented. Water vapour transmission rates (WVTR) show values of the order of 10 (3) g/m(2)/d at 38 degrees C, 90% RH on planarized PEN webs (pPEN) when ozone is used as the oxidizing precursor for Al2O3 deposition. OLED encapsulated with such diffusion barriers display few dark spots observed over 2000 h after deposition and for aging under ambient conditions. Diffusion barriers deposited using water as the oxidizing precursor for Al2O3 result in at least 10 times lower WVTR on pPEN webs (10 (4) g/m(2)/d). However, these water based diffusion barriers are incompatible with OLEDs such that the latter show extensive black spot formation (areas of no visible luminescence) immediately after deposition. Finally through the growth of these initial black spots, more than 40% loss in initial luminescence occurs after merely 900 h of operation. In this report, we introduce a new methodology for OLED encapsulation using a two step process where 10 nm thick ozone Al2O3 based nanolaminate diffusion barrier is followed by a 90 nm thick water Al2O3 based diffusion barrier (keeping TiO2 precursors always the same). With this novel diffusion barrier stack, no visible black spot growth is observed over 2000 continuous operation hours under ambient conditions. Simultaneously, high OLED luminescence representing 90% of the initial luminescence value, which is measured at t = 0 is maintained after 2000 h of operation. Low WVTR values in the 10 (4) g/m(2)/d range on pPEN webs are consistently measured in these essentially water based barrier layers with only 10 nm thick starting ozone Al2O3 based nanolaminate diffusion barriers. The results reported here have implications on developing methodologies for ultra high performance, OLED compatible diffusion barriers by ALD. (C) 2014 Elsevier B.V. All rights reserved.