In 2023, we reported on research conducted at Germany’s Max Planck Institute, led by Prof. Paul W.M. Blom, that looks into single-layer OLED devices. In such devices, a single TADF OLED emitter layer is sandwiched between two electrode – a much simpler design compared to commercial OLED devices that use multilayer stacks, sometimes with 10 or more layers. The researchers say that in fact it is possible to develop highly efficient OLEDs with just the TADF emitter – and have demonstrated 100% IQE single-layer devices, with an EQE of 27.7%. In 2024, the reported the highest performance TADF system.
The researchers now report that they have designed a single-layer hyperfluorescence OLED device, which is both efficient and stable. This new research was led by Prof. Blom and Prof. Wetzelaer at the Max Planck Institute.
The researchers explain that one of the problems, though with TADF OLED devices, is the broad emission spectrum. A solution to this is the use of hyperfluorescence, that combines the TADF emitter with a fluorescence emitter, which results in an efficient emitter with a narrowband emission spectrum. The problem with HF systems, though, according to the researchers, is that typcially the incorporation of the fluorescenece emitter leads to charge carrier trapping that strongly reduces the OLED efficiency since it causes unbalanced transport.
In this new research, the researchers show that a single-layer hyperfluorescence system does not only offer a narrow spectrum – it can be blue-shifted, without loss of efficiency due to trapping. This single-layer OLED with narrow blue spectrum reaches a LT50 of 800hrs at 1000 cd/m2, which is very high for TADF based blue OLEDs. The researchers say that this results reconfirms their earlier statement that single-layer OLEDs are intrinsically more stable than multi-layer OLEDs.