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.
Blueprint
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.
