Periodic Reporting for period 1 - SCOLED (Strong-coupling-enhanced nanoparticle array organic light emitting diode)
Reporting period: 2023-05-01 to 2024-04-30
Light-emitting devices (LEDs) are a crucial part of everyday life as they are commonly used in displays as well as in general lighting applications. LEDs are more energy efficient and have longer life spans than light bulbs and are hence considered to be more sustainable. Usually, LEDs consist of inorganic materials which, however, are oftentimes toxic, scarce, and their production is energy intensive. One possibility to overcome these aspects is to create LEDs from organic materials (OLEDs), which can already be found in displays. OLEDs can be fabricated from earth-abundant non-toxic materials using energy-efficient processes. However, state-of-the-art OLEDs suffer from a low efficiency blocking their widespread employment in lighting applications. In the SCOLED project, OLEDs will be combined with nanoparticle arrays to enhance the coupling between light and matter in the OLEDs to enhance the efficiency to a level competitive with inorganic LEDs. The concept of strong coupling (SC) will be exploited for efficiency enhancement, leading to SCOLEDs. Other objectives include colour, polarization, and directional control of the emitted light. We use analytic theory, numerical simulations, and nanofabrication to design SCOLEDs which will then be characterized optically and electronically. The goal of SCOLED is the proof-of-principle demonstration of an OLED with high external quantum efficiency with control over the properties of the emitted light. The prospect of the project is a technology that will dramatically reduce the environmental impact of LED technology and widen the range of OLED applications.
We designed the geometries of the first nanoparticle arrays as well as the size and shape of the nanoparticles. These parameters provide control over the colour and polarization of the emitted light while enabling colour stability over a wide angular range. The first experimental proof of angularly uniform emission from these structures has been realized. In addition, suitable emitting materials in blue, green, and red have been identified as well as an evaluation approach to assess the optical properties of molecular materials has been developed. The nanoparticle size and shape, as well as array geometries have been optimized for these emitters using numerical simulations. A simulation tool for optimization of OLED structures has been developed, a fabrication workflow for OLEDs has been designed and several setups for experimental characterization of OLEDs have been taken into use. Furthermore, nanoparticle and array geometries were optimized to form strong coupling with a chosen material, which indeed showed strong coupling. A theoretical description describing the influence of strong coupling on the internal dynamics in molecular systems as well as procedure to verify if strong coupling occurs are being developed. Finally, we proved experimentally that simple nanoparticle arrays can lead to emission enhancement in simplified structures.
The first results showing strong coupling between nanoparticle arrays and emitters, emission enhancement in simple OLED structures with simple nanoparticle arrays as well as angularly uniform emission by specifically designed array geometries and nanoparticle shapes and sizes are very promising for the outcome of the project. Further research is required, where the next steps include fabrication and experimental characterization of electrically pumped (optimized) OLEDs with and without nanoparticle arrays while simultaneously combining the arrays which provide angularly uniform emission with the identified materials to further develop the control over colour, polarization and angular emission of the light. In addition, five possible inventions have been identified.