A fundamental loss mechanism in semiconductors is the emission of light to maintain the thermodynamic equilibrium between material and environment. It is precisely this balance between light absorption and emission in the semiconductors that is responsible for the fact that "an ideal solar cell is also an ideal light-emitting diode", explains Johannes Benduhn the basic assumption of the Organic Solar Cells (OSOL) Group at the Institute of Applied Physics at Dresden University of Technology.
However, organic solar cells are subject to further loss mechanisms that have so far stood in the way of this assumption. These mechanisms cause the recombination of charge carriers in the form of heat, without the emission of light ("non-radiating") and thus reduce the tappable voltage and consequently the efficiency of the solar cell. These non-radiative voltage losses are one of the main reasons for the lower efficiency of organic solar cells compared to established technologies currently used on rooftops.
With the newly developed organic solar cells, the OSOL Group was able to keep these voltage losses comparatively low and thus pave the way for efficient and completely new areas of application. The international research team has succeeded in developing combinations of organic semiconductors that are based on electron acceptor and electron donor transitions and function both as solar cells and LEDs. The results from this research work extend the current understanding of organic semiconductors. For the first time, they combine the physical description of organic solar cells and OLEDs.
These findings will enable commercially available OLEDs in smartphone displays or television screens to be made more energy-efficient in the future. The newly developed organic solar cells can also be used for the efficient conversion of ultraviolet and blue photons into electrical power, e.g. in indoor applications for the electrical supply of Internet of things devices or as semi-transparent solar cells in glass facades.