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 α-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 α-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 α-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 σUPS = 0.22 eV and that derived from simulations is σsim = 0.23 eV