Using materials provided by Solvay a starting point hybrid OLED architecture has been identified and implemented at both Holst Center and University of Valencia. The materials required for the preparation of the OLEDs have successfully been upscaled by Solvay reducing significantly the side products and waste. Due to the combined efforts very similar performances are obtained using a standardized OLED at Holst and University of Valencia. This is an important achievement and prerequisite for the rapid implementation of further material and device improvements. The performance of this initial stack was promising yet the reproducibility was not. This was due to the use of one difficult to handle material. Using the expertise of Osram, Holst and Univ. of Valencia an alternative material has been identified that is much easier to handle and leads to reproducible results. One of the essential layers in the OLED stack contains a crosslinkable hole transport material that proved difficult to produce. The consortium identified in a combined effort an interesting alternative material that leads to OLEDs with similar performances. This material in addition can be crosslinked at temperatures compatible with flexible substrates, something that was not feasible with the previous material. Partner EPFL has applied for a patent for this new class of materials and Solvay has optimized the synthesis leading to the availability of large amounts of this material. Interested parties can contact Solvay (
Vincent.schanen@solvay.com) to discuss conditions for supply.
A large number of emitters have been developed, ranging from blue light-emitting phosphorescent and fluorescent molecules to green light-emitting perovskites.
SOLEDLIGHT also aims to prepare OLED using only solution based processes (coating) on flexible substrates. This implies that the processing steps need to be below the softening temperature of the plastic substrates used. Additionally, as high efficiency OLEDs consist of at least 4 separate layers, each of several tens of nanometer thickness, it is important to prevent the removal of previously deposited layers due to the solvents. To achieve this, Imperial College has prepared molecules that can insolubilize the active materials in the different OLED layers. When the active molecules are polymers this approach works, yet we have found that for smaller active molecules it is more difficult to insolubilize them. Using a Hansen solubility identification test the consortium was able to identify a large number of solvents with potential orthogonality towards each other. Obviously, the type of material used in the stack is of large importance and a table demonstrating some options, is publicly available from Deliverable 5.5 (dissemination kit) and posted on the soledlight webpage (
http://www.soledlight.eu/deliverables.php?menu=deliverables(opens in new window)). Part of the OLED stack contains propietory molecules and therefore, these are not included in the before listed overview. We were, able to identify two solvents that enable the formation of a 4 and 5 layer OLED using small molecular weight components in three layers of the stack. This demonstrates that solution processing of OLEDs is feasible. Depending on the type of materials employed, efficiencies reaching 15 lm/W have been achieved for white light-emitting devices.
We have implemented perovskite emitters and reached very promising performance, reaching 50 lm/W for green light-emitting LEDs. Single side contact layer large area OLEDs answering the expectations of designers were developed allowing for further form factor freedom. Using sheet to sheet processing large area flexible OLEDs were prepared using three layers from solution that operate at a power efficiency above 50 lm/W when suitable light outcoupling foils are implemented.
Upscaling of the process of making solution processable OLEDs has been demonstrated on a roll to roll pilot line with a speed of 10 meters per minute, leading to OLEDs that exhibit 80 % of the performance parameters of similar OLEDs produced by sheet to sheet processes.
SOLEDLIGHT does not only aim to prepare OLEDs, but also to integrate them into Luminaires. Out of a few design options, the Flamingo luminaire emerged that uses 5 large area OLED panels that are special in that they have only one contact side, allowing for additional design freedom. See a picture of the luminaire and some of the project collaborators below.
The flexible OLED foils were also integrated into a luminaire, which was selected from several candidates and an image is shown below of luminaire, referred to as ASPO.
A “Lessons learned” document is available from the SOLEDLIGHT Webpage (www.soledlight.eu/results/public-report).
