Aims

The overall objective of the PHEBE project was to develop innovative, high-efficiency, blue emitters for white OLEDS to create a major breakthrough in the cost performance of OLED lighting. To produce the innovative blue emitters, two new types of molecular systems – without rare earth complexes - were investigated:

  • Intramolecular charge transfer systems that enable thermally activated delayed fluorescence (ICT-TADF)
  • Intermolecular exciplex charge transfer systems that enable thermally activated delayed fluorescence (Exciplex- TADF)

In order to develop the ICT-TADF and Exciplex-TADF based emitters, the following scientific and technical objectives were targeted:

  • Objective 1: Screen potential ICT-TADF and Exciplex-TADF compounds with theoretical models
  • Objective 2: Synthesise the most promising ICT-TADF and Exciplex-TADF model compounds
  • Objective 3: Characterise and select the best ICT-TADF and Exciplex-TADF synthesised compounds
  • Objective 4: Design white stack units employing the selected TADF based emitter and block materials
  • Objective 5: Design close-to-production OLED lighting panel demonstrators

To evaluate the performance of the new blue emitters, OLED lighting panel demonstrators were produced and tested.

The PHEBE project was undertaken by a strong consortium of partners spanning the value chain for the development and commercialisation of the new, high-efficiency, blue emitters for white OLEDS: OLED lighting research organisations (Durham University, Technical University of Dresden and Kaunas Technological University) and OLED component producer (Novaled).

Results

During the project, the consortium was able to produce blue emitters based on phenylcarbazole organic material that demonstrated TADF and these blue emitters had good external quantum efficiency of up to 18%.

However, the 50% lifetime for these blue emitters was very short – just 2 hours – so the consortium is still quite a way off from having new material that can be used for OLED lighting.

The consortium believes the emitter’s lifetime issue is dependent on two factors:

  • The host material used together with the emitter material needs to be very carefully selected. Previously, it was thought that the lifetime was independent of the host.
  • The synthesised organic material used for the emitter needs to be extremely pure, as close to 100% as possible.

Although PHEBE did not meet its overall objective, it generated new knowledge and advanced the state-of-the-art of TADF materials. The consortium published over 25 journal articles – including two in Nature Communications - and filed patents for three new families of organic materials.