Photoluminescence (PL) spectroscopy has been performed in-situ on iridium(III) ionic transition metal complex (iTMC)-
based sandwich-type light-emitting electrochemical cells (LECs) during device operation and after switch-off. It is
demonstrated that driving the device leads to a considerable decrease of the PL intensity of the active layer. Two
different time regimes for this decrease have been identified. The first one is characterized by a complete recovery of the
PL after the device is turned off corroborating the existence of dynamically formed doped regions also in iTMC-based
LECs. In the second regime the PL does not completely recover which is attributed to a permanent degradation of the
active layer that is the main source for the low lifetime of the devices.
Additionally, it is demonstrated how to externally stabilize the dynamic configuration leading to a half lifetime in excess
of 1000 hours at simultaneous high brightness of more than 1000 cd/m2 and fast turn-on of less than one second.
Typically high efficient OLED device structures are based on a multitude of stacked thin organic layers prepared by
thermal evaporation. For lighting applications these efficient device stacks have to be up-scaled to large areas which is
clearly challenging in terms of high through-put processing at low-cost. One promising approach to meet cost-efficiency,
high through-put and high light output is the combination of solution and evaporation processing. Moreover, the
objective is to substitute as many thermally evaporated layers as possible by solution processing without sacrificing the
device performance. Hence, starting from the anode side, evaporated layers of an efficient white light emitting OLED
stack are stepwise replaced by solution processable polymer and small molecule layers. In doing so different solutionprocessable
hole injection layers (= polymer HILs) are integrated into small molecule devices and evaluated with regard
to their electro-optical performance as well as to their planarizing properties, meaning the ability to cover ITO spikes,
defects and dust particles. Thereby two approaches are followed whereas in case of the "single HIL" approach only one
polymer HIL is coated and in case of the "combined HIL" concept the coated polymer HIL is combined with a thin
evaporated HIL. These HIL architectures are studied in unipolar as well as bipolar devices. As a result the combined HIL
approach facilitates a better control over the hole current, an improved device stability as well as an improved current
and power efficiency compared to a single HIL as well as pure small molecule based OLED stacks. Furthermore,
emitting layers based on guest/host small molecules are fabricated from solution and integrated into a white hybrid stack
(WHS). Up to three evaporated layers were successfully replaced by solution-processing showing comparable white
light emission spectra like an evaporated small molecule reference stack and lifetime values of several 100 h.
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