Periodic Reporting for period 2 - SOLEDLIGHT (Solution Processed OLEDs for Lighting)
Berichtszeitraum: 2016-07-01 bis 2017-12-31
Glass OLED products prepared by vacuum evaporation techniques have been demonstrated with good performances, yet the main bottle neck for larger market introduction is the high cost. At high production volumes the cost of OLED production is directly related to the efficiency of materials usage which is estimated to be 70 % for vacuum deposition and 90 % via solution processing.
Hence, roll-to-roll solution processed OLEDs, will lead to a significant price reduction due to more efficient organic material usage, lower capital investments and higher throughput. Additionally, these OLEDs will be produced directly on flexible substrates allowing for new light weight and space saving designs.
Society will benefit as with the availability of these flexible efficient lighting sources electricity consumption will be reduced.
SOLEDLIGHT has assembled a consortium comprising a Osram (leading OLED manufacturer and integrator), Solvay (leading OLED materials manufacturer), TNO/Holst Centre (an excellence centre for organic devices with a state-of-the-art R2R line and leading universities in the field (Univ. Valencia, EPFL and Imperial College).
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). 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).
SOLEDLIGHT has designed a single side contactable OLED showing uniform light emission over the complete area that are easily integrated in a demonstrator Luminaire.
Flexible OLED luminaire demonstrates the design features of the thin film OLEDs, in particular the off status of these foils, showing the mirror effect.
Upscaling to make these flexible OLEDs on R2R equipment has been demonstrated. These achievements are and will be implemented in other flexible opto-electronic devices, such as perovskite solar cells.
Perovskite emitters were identified as interesting low cost semiconductor light emitting materials, which will be further evaluated in a joined project that is under preparation by some of the partners.