Transparent Ag-Free OLED Fabricated by OVPD Using Thin Au Contacts

Abstract

ABSTRACTWe demonstrate Ag-free transparent OLED (TOLED) fabricated by organic vapor phase deposition (OVPD) using thin Au contacts. Three types of TOLED devices have been studied. The first one has been deposited on ITO substrates to compare thin Ag and Au films as top cathodes. A 6-fold increase in operational lifetime (LT50, 4 mA/cm2) from 27 h to 172 h can be observed when replacing Ag by Au while maintaining similar electro-optical characteristics. Furthermore, a second type of TOLED on thin Au films, replacing ITO and suppressing laterally guided modes [1], has been studied. TOLED on ITO substrates and on thin Au films exhibit very low onset voltages of 2.2 V. Both types show about 30% transparency in the VIS light region and emit orange light with a peak wavelength of 608 nm from either side with a total EQE of about 9% (measured at 1000 cd/m2 in sum). The third type of TOLED was fabricated with an inverted structure, with the aim to further increase operational lifetime by burying the reactive LiF/Al electron injection layer (EIL). This will make the EIL less accessible for oxygen and moisture. Our results show difficulties in electron injection when depositing the organic stack on Al/LiF, which may be attributed to an insufficient thermal activation of the EIL.