Towards efficient next generation light sources: combined solution processed and evaporated layers for OLEDs

D. Hartmann; W. Sarfert; S. Meier; H. Bolink; S. García Santamaría; J. Wecker

doi:10.1117/12.857035

20 May 2010 Towards efficient next generation light sources: combined solution processed and evaporated layers for OLEDs

D. Hartmann, W. Sarfert, S. Meier, H. Bolink, S. García Santamaría, J. Wecker

Author Affiliations +

Proceedings Volume 7722, Organic Photonics IV; 77220P (2010) https://doi.org/10.1117/12.857035
Event: SPIE Photonics Europe, 2010, Brussels, Belgium

Abstract

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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D. Hartmann, W. Sarfert, S. Meier, H. Bolink, S. García Santamaría, and J. Wecker "Towards efficient next generation light sources: combined solution processed and evaporated layers for OLEDs", Proc. SPIE 7722, Organic Photonics IV, 77220P (20 May 2010); https://doi.org/10.1117/12.857035

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