In the past 25 year of research on organic semiconductors, organic solar cells and organic light-emitting diodes (OLEDs) were considered to be mutually exclusive devices. A team of physicists headed by Prof. Koen Vandewal from the Technische Universität Dresden has now succeeded in fabricating an organic solar cell, which simultaneously functions as an OLED. Their findings were recently published in the internationally renowned journal Nature Materials.

A fundamental loss mechanism in semiconductors is the emission of light to maintain the thermodynamic balance of the material with its environment. This necessary balance between light absorption and emission in semiconductors is responsible for ensuring that "an ideal solar cell is also an ideal light-emitting diode," says Johannes Benduhn from the Organic Solar Cells (OSOL) group at the Institute of Applied Physics.

However, organic solar cells are subject to further loss mechanisms and therefore opposed this assumption so far. Instead of generating light, a large part of charge carriers recombines in the form of heat ("non-radiative"). This leads to a lower voltage and consequently a reduction of the power conversion efficiency, one of the main reasons why organic solar cells are not as efficient as established technologies you can find on rooftops nowadays. 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 higher efficiencies, but also completely new fields of application.

© Benduhn/Schmidt, TUD

The international research team has succeeded in developing combinations of organic semiconductors based on electron acceptor and electron donor heterojunctions that function as both solar cells and LEDs. The results of this research significantly extend the current understanding of organic semiconductors and combine for the first time the physical description of organic solar cells and OLEDs.

These findings will benefit both OLEDs and organic solar cells and contribute to the development of more energy-efficient smartphone displays or television screens. The newly developed photovoltaic devices can 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. 

About the Organic Solar Cell (OSOL) Group at the Institute of Applied Physics at TU Dresden

The OSOL Group is part of the Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and the Institute of Applied Physics of TU Dresden.  The group has been headed by Prof. Koen Vandewal, who now researches and teaches at the University of Hasselt in Belgium. One research focus of the OSOL group are photoactive organic semiconductors and their application in solar cells and photodetectors. Current research focuses on basic recombination processes, development and synthesis of new materials, design of new device architectures and optimisation of organic solar cells.

Original Publication:

Sascha Ullbrich, Johannes Benduhn, Xiangkun Jia, Vasileios C. Nikolis, Kristofer Tvingstedt, Fortunato Piersimoni, Steffen Roland, Yuan Liu, Jinhan Wu, Axel Fischer, Dieter Neher, Sebastian Reineke, Donato Spoltore and Koen Vandewal, Emissive and charge-generating donor–acceptor interfaces for organic optoelectronics with low voltage losses. Nature Materials 2019 (https://doi.org/10.1038/s41563-019-0324-5)

Media contact:

Johannes Benduhn
Institute of Applied Physics
Tel: +49(0)351 463 36446
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