Functional Interfaces For Transparent Organic Electronic Devices: Consistent Description Of Charge Injection By Combining In Situ Xps And Current Voltage Measurements With Self-Consistent Modeling

The interface properties between Sn-doped In2O3 (ITO) and the organic semiconductor alpha-NPD are studied using in situ X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) as well as with in situ current-voltage analysis in combination transport simulations using a self-consistent mean field model. In particular, ITO is sputtered onto alpha-NPD as required for transparent or inverted organic light-emitting diodes. We identify deposition conditions, which leave the organic molecules intact. The barrier heights determined by XPS/UPS for the inverted interfaces between undoped and doped alpha-NPD and ITO are 1.0 and 1.1 eV, respectively. These are in good agreement with barrier heights extracted from current-voltage simulations if the band width of the highest occupied molecular orbital (HOMO) is taken into account. The HOMO bandwidth determined by UPS is sigma(UPS) = 0.22 eV and that derived from simulations is sigma(sim), = 0.23 eV.