We report on the tailoring strong-light matter coupling and polariton formation in organic semiconductors, with particular focus on the design of OLEDs with angle-independent emission and polariton lasers with reduced thresholds and fully metallic contacts.
With ever more stringent colour requirements in the display industry, there is a need for OLEDs with more saturated-colour emission. The use of strong micro-cavities is a potential solution but can introduce undesired changes in colour with observation angle. By introducing an assistant absorber layer into microcavity OLEDs, we create exciton polaritons that inherit the angle insensitivity of molecular absorption and the narrow linewidth of the cavity mode. We also demonstrate that our approach can be generalized beyond OLEDs, e.g. to obtain optical filters with sharp and angle independent spectral features.
In addition, we discuss work on polariton lasers that exploit conformation, molecular alignment, and the disorder introduced by micro-domains in liquid crystalline polymer films to enhance lasing performance. This then allows us to replace the dielectric mirrors of these lasers with electrically conducting metal mirrors.
The outcoupling efficiency of OLEDs can be significantly enhanced by orienting the emitter molecules horizontally within the film. While some guidelines have been developed to control molecular orientation in OLEDs[1], our understanding of the factors at play remains limited by the fact that current techniques only obtain average values of what in reality is a distribution of orientations. Here, we develop a method to obtain orientation distributions of emitters in thermally evaporated films of host-guest emissive layers relevant to OLED displays[2]. We achieve this by adapting out-of-focus fluorescence imaging of individual molecules for use in thermally evaporated systems. We show how the orientation distribution of emitters depends on processing conditions and on the nanoscale environment of the emitters. Crucially, we also show that emitters can adopt different orientation distributions that would be indistinguishable in ensemble-averaging measurements.
[1] F. Tenopala-Carmona, … M. C. Gather, Adv. Mater. 2021, 33, 2100677
[2] F. Tenopala-Carmona, … M. C. Gather, Nat. Comm. 2023, 14, 6126
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