Combined thermal evaporated and solution processed organic light emitting diodes

Abstract

Highly efficient, partly solution processed phosphorescent red, green and white organic light emitting diodes with small molecular weight host materials are prepared from commercially available starting compounds. Starting from an evaporated reference device, layers are stepwise replaced by solution processed layers. Replacing the evaporated hole transport layer by a solution processed polymer interlayer does not affect the performance and allows spincoating of the emissive layer after annealing of the polymer. Devices with, next to the spincoated hole injection and transport layer, a solution processed emission layer show similar characteristics and efficiencies as the reference device. Additionally, white light emitting devices are demonstrated in which the first emissive layer is solution processed, for which lifetimes in excess of 1000 h are achieved. Thus, we show that, in order to reduce production costs, solution processing can be used as an alternative to – and in conjunction with – Thermal evaporation.