Nav: Home

Tuning the energy levels of organic semiconductors

July 08, 2019

A diverse set of experiments supported by simulations were able to rationalize the effect of specific electrostatic forces exerted by the molecular building blocks on charge carriers. The study was published recently in Nature Communications.

In electronic devices based on organic semiconductors such as solar cells, light-emitting diodes, photodetectors or transistors, electronic excitations and charge transport levels are important concepts to describe their operation principles and performances. The corresponding energetics, however, are more difficult to access and to tune than in conventional inorganic semiconductors like silicon chips, which stands as a general challenge. This applies both to the measurement and to the controlled influence from outside.

One tuning knob exploits the long-range Coulomb interactions, which is enhanced in organic materials. In the present study, the dependence of the energies of charge transport levels and of excitonic states on blend composition and molecular orientation in the organic material is explored. Excitons are bound pairs of an electron and a hole that are formed in the semiconductor material by light absorption. Scientists refer to blend composition when the components consist of different organic semiconducting materials. The findings demonstrate that the energetics in organic films can be tuned by adjusting a single molecular parameter, namely the molecular quadrupole moment in the pi-stacking direction of the molecules. An electric quadrupole can consist of two positive and two equally strong negative charges which form two oppositely equal dipoles. In the simplest case, the four charges are alternately arranged at the corners of a square.

The authors further link device parameters of organic solar cells such as the photovoltage or the photocurrent to this quadrupole moment. The results help to explain recent breakthroughs of device efficiency in organic solar cells, which are based on a new class of organic materials. As the observed electrostatic effect is a general property of organic materials, including so-called "small molecules" and polymers, it can help to improve the performance of all types of organic devices.
Paper title: "Impact of molecular quadrupole moments on the energy levels at organic heterojunctions" (Nature Communications)
DOI: 10.1038/s41467-019-10435-2
Authors: M. Schwarze, K. S. Schellhammer, K. Ortstein, J. Benduhn, C. Gaul, A. Hinderhofer, L. Perdigón Toro, R. Scholz, J. Kublitski, S. Roland, M. Lau, C. Poelking, D. Andrienko, G. Cuniberti, F. Schreiber, D. Neher, K. Vandewal, F. Ortmann, Karl Leo

About the Computational Nanoelectronics Group:

The research group at the Center for Advancing Electronics Dresden (cfaed) headed by Dr. Frank Ortmann investigates electronic properties and charge transport properties of novel semiconductor materials. Here, organic semiconductors are currently an important focus of the work, which is funded by the German Research Foundation under the Emmy Noether Program. The group has been based at the cfaed since 2017. Info:

Media inquiries:

Prof. Karl Leo
Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP)
TU Dresden

Dr. Frank Ortmann
Center for Advancing Electronics Dresden (cfaed)
Technische Universität Dresden
Tel.: +49 351 463-43260

Matthias Hahndorf
Center for Advancing Electronics Dresden (cfaed)
Technische Universität Dresden
Head of Communications
Tel.: +49 351 463-42847


cfaed is a microelectronics research cluster funded by the German Excellence Initiative. It comprises 11 cooperating institutes in Saxony, host university is the Technische Universität Dresden (TUD). About 300 scientists from more than 20 countries investigate new technologies for electronic information processing. These technologies are inspired by innovative materials such as silicon nanowires, carbon nanotubes or polymers or based on completely new concepts such as the chemical chip or circuit fabrication methods by self-assembling structures such as DNA-Origami. The orchestration of these new devices into heterogeneous information processing systems with focus on their resilience and energy-efficiency is also part of cfaed's research program which comprises nine different research paths.

Technische Universität Dresden

Related Solar Cells Articles:

Perovskite solar cells get an upgrade
Rice University materials scientists find inorganic compounds quench defects in perovskite-based solar cells and expand their tolerance of light, humidity and heat.
Can solar technology kill cancer cells?
Michigan State University scientists have revealed a new way to detect and attack cancer cells using technology traditionally reserved for solar power.
Solar cells with new interfaces
Scientists from NUST MISIS (Russia) and University of Rome Tor Vergata found out that a microscopic quantity of two-dimensional titanium carbide called MXene significantly improves collection of electrical charges in a perovskite solar cell, increasing the final efficiency above 20%.
Welcome indoors, solar cells
Swedish and Chinese scientists have developed organic solar cells optimised to convert ambient indoor light to electricity.
Mapping the energetic landscape of solar cells
A new spectroscopic method now makes it possible to measure and visualize the energetic landscape inside solar cells based on organic materials.
Solar energy becomes biofuel without solar cells
Soon we will be able to replace fossil fuels with a carbon-neutral product created from solar energy, carbon dioxide and water.
A good first step toward nontoxic solar cells
A team of engineers at Washington University in St. Louis has found what they believe is a more stable, less toxic semiconductor for solar applications, using a novel double mineral discovered through data analytics and quantum-mechanical calculations.
Organic solar cells will last 10 years in space
Scientists from the Skoltech Center for Energy Science and Technology, the Institute for Problems of Chemical Physics of RAS, and the Department of Chemistry of MSU presented solar cells based on conjugated polymers and fullerene derivatives, that demonstrated record-high radiation stability and withstand gamma radiation of >6,000 Gy raising hopes for their stable operation on the near-earth orbit during 10 years or even longer.
Next-gen solar cells spin in new direction
A nanomaterial made from phosphorus, known as phosphorene, is shaping up as a key ingredient for more sustainable and efficient next-generation perovskite solar cells.
Caffeine gives solar cells an energy boost
Scientists from the University of California, Los Angeles (UCLA) and Solargiga Energy in China have discovered that caffeine can help make a promising alternative to traditional solar cells more efficient at converting light to electricity.
More Solar Cells News and Solar Cells Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#542 Climate Doomsday
Have you heard? Climate change. We did it. And it's bad. It's going to be worse. We are already suffering the effects of it in many ways. How should we TALK about the dangers we are facing, though? Should we get people good and scared? Or give them hope? Or both? Host Bethany Brookshire talks with David Wallace-Wells and Sheril Kirschenbaum to find out. This episode is hosted by Bethany Brookshire, science writer from Science News. Related links: Why Climate Disasters Might Not Boost Public Engagement on Climate Change on The New York Times by Andrew Revkin The other kind...
Now Playing: Radiolab

Breaking Bongo
Deep fake videos have the potential to make it impossible to sort fact from fiction. And some have argued that this blackhole of doubt will eventually send truth itself into a death spiral. But a series of recent events in the small African nation of Gabon suggest it's already happening.  Today, we follow a ragtag group of freedom fighters as they troll Gabon's president - Ali Bongo - from afar. Using tweets, videos and the uncertainty they can carry, these insurgents test the limits of using truth to create political change and, confusingly, force us to ask: Can fake news be used for good? This episode was reported and produced by Simon Adler. Support Radiolab today at