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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - SOLEDLIGHT (Solution Processed OLEDs for Lighting)

Teaser

Summary

Highly efficient organic electroluminescent devices (OLEDs) are a technology that promises to reduce significantly the electricity consumption. The estimated market for OLED lighting products is large ($8 billion) and European lighting manufacturers are ideally positioned to capture a large part of it.
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).

Work performed

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). 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

Final results

SOLEDLIGHT has developed a crosslinkable hole transporting material compatible with flexible plastic substrates. 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.

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.