Researchers at the Fraunhofer Institute for Photonic Microsystems IPMS have developed novel OLED stacks that enable exceptionally bright microdisplays. These were presented for the first time at the SPIE AR VR MR 2025 trade fair in San Francisco.
Users of data glasses for augmented reality (AR) require particularly bright displays in daylight in order to be able to see content clearly. High brightness and low power consumption are therefore crucial development goals, as optical systems such as AR glasses have high brightness losses and the power consumption of portable devices is limited by battery storage.
Fraunhofer IPMS is now presenting a highly efficient, single-color OLED microdisplay with a brightness of over 70,000 nits. The OLED stack used even achieves over 200,000 nits on reference substrates. The researchers achieved the high brightness by stacking OLED layers, whereby the individual layers are 'connected in series'. This increases the brightness with each additional unit without increasing the current density in the component. In this way, either extremely high brightness can be achieved or the current density, which is decisive for the service life, can be reduced for a given brightness.
Narrow-band emission with high brightness
According to the researchers involved, measurements have shown that in comparison between a 1-unit and 2-unit OLED, the LT95 service life, i.e. the drop in brightness by 5%, can be significantly improved from 900 to 1300 hours at 50,000 nits.
The power efficiency and brightness of 1-, 2- and 3-unit stacked OLEDs were first evaluated on passive test substrates and were then successfully transferred to 0.62 ″ CMOS backplanes with SXGA resolution. This revealed new challenges for further research: While the distance between the subpixels in conventional OLED displays is often several tens of micrometers, in microdisplays it is only a few hundred nanometers. This can lead to crosstalk between neighboring pixels with thicker layer stacks and multiple stacked OLEDs in microdisplays. Solutions to reduce this crosstalk are in preparation.
In addition, the work has shown that narrow-band emission with high brightness can be achieved through multiple stacking. Here, the spectral emission can be specifically adapted. This means that optical concepts with special requirements, such as waveguides or holographic elements, can be used.
The researchers are convinced that the ongoing development towards ever higher brightness and improved lifetimes will secure OLED technology a permanent place in the field of AR applications. Nevertheless, there is a continuous need for research, e.g. into optical crosstalk, improved OLED materials and innovative backplane architectures.
