Single-molecule OLED lights up upon charging: towards energy-efficient light sources

In today’s world of increasing energy use, we need to find new ways for eco-friendly sources. Organic light emitting diodes (OLEDs) are promising for energy-efficient light sources. This technology will help us to develop machines and devices that are smaller, faster and greener. However, how OLEDs exactly work is not entirely clear. Physicists at the Institute for Molecules and Materials (IMM) of Radboud University discovered that if electricity goes through OLEDs, molecules are charged either positively or negatively, depending on the voltage. By this charge the molecule produces light, which is more energy-friendly than traditional methods. The work has recently been published in Physical Review Research.

Organic Light Emitting Diode (OLED) technology uses organic compounds – molecules – to emit light when an electric current flows through the device. Compared to inorganic semiconductor LEDs, OLED production requires lower process temperatures and hence consumes much less energy. Moreover, the optical properties of OLED molecules can be designed by chemists to reach internal quantum efficiencies near 100%, making OLED technology potentially far superior over lighting alternatives. Applied research aims to improve the efficiency of the device technology as it continuously evolves. However, on the microscopic level, the fundamental processes that convert an electric current into light are not well understood to date.

Charging molecules

Using a technique called scanning tunneling microscopy, the research team led by Daniel Wegner studied under which conditions a single molecule called zinc phthalocyanine (ZnPc) emits light. The researchers found that when a current passes through this “single-molecule OLED”, in almost all situations the ZnPc molecule becomes charged prior to emitting light. The team also observed that the different colours emitted by OLED changes, depending on the applied voltage that determines whether the molecule is positively or negatively charged. This behavior could be explained by which molecular orbitals are involved in the current flowing through the device. “The charging process initiates the light emission, and the colour of the emitted light can be altered by reversing the voltage”, researcher Daniel Wegner explains.


The research study provides a blueprint for future systematic research to unravel how a current flow in an electroluminescent device such as an OLED eventually leads to light and what the role the molecular properties play. Beyond this, It highlights the importance of transiently charged states of molecules in the design and optimization of OLEDs.

Scanning Probe Microscopy

Dr. Daniel Wegner is researcher in the Scanning Probe Microscopy department. The research group is part of IMM. The group aims to understand new phases of matter, understanding how molecular interactions lead to macroscopic properties and studying structural, electronic and magnetic properties of surfaces. They focus on magnetic and electronic imaging in cryogenic environments in magnetic fields.

Charged molecules enable light emission of OLED
Literature reference

Bipolar single-molecule electroluminescence and electrofluorochromism
Tzu-Chao Hung, Roberto Robles, Brian Kiraly, Julian H. Strik, Bram A. Rutten, Alexander A. Khajetoorians, Nicolas Lorente, and Daniel Wegner
Physical Review Research (2023)


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Sustainability, Innovation, Molecules and materials, Science