Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New Understanding Could Result in More Efficient Organic Solar Cells

06.02.2014
The goal of making cheap organic solar cells may have gotten a little more approachable with a new understanding of the basic science of charge separation presented in a paper published online today, February 3, in Nature Communications.

Co-authored by Penn State electrical engineer Noel Giebink with lead author Bethany Bernardo, an undergraduate in his group, and colleagues at IMEC in Belgium, Argonne National Lab, Northwestern, and Princeton, the paper suggests design rules for making more efficient solar cells in the future.


Giebink, Penn State

An electron wave function, indicated by orange shading, spreads across several nanocrystalline fullerene molecules in this representation of an organic solar cell heterojunction.

Organic solar cells currently have a top efficiency of approximately 10 percent in the laboratory, much less than inorganic single crystal silicon. One of the challenges to realizing efficient organic cells lies in separating the strongly bound pairs made up of a negatively charged electron and its positively charged hole that result from light absorption, collectively referred to as an exciton. The electron and hole need to be separated in order to make a current.

The way this is done is by creating a heterojunction, which is two different organic semiconductors next to each other, one of which likes to give up an electron and the other which accepts the electron, thereby splitting the original exciton into an electron and hole residing on nearby molecules. A long-standing question in the field, however, is how the nearby electron and hole – still strongly attracted to each other at this stage – manage to separate completely in order to generate current with the efficiency observed in most solar cells.

Over the past few years, a new perspective has proposed that the high separation efficiency relies on a quantum effect – the electron or hole can exist in a wavelike state spread out over several nearby molecules at the same time. When the wave function of one of the carriers collapses at a location far enough away from its partner, the charges can separate more easily. Giebink and colleagues’ work provide compelling new evidence to support this interpretation and identify nanocrystallinity of the common acceptor material made of C60 molecules (also known as fullerenes or buckyballs) as the key that allows this delocalization effect to take place.

This local crystalline order appears to be critical to efficient photocurrent generation in organic solar cells, says Giebink. “A common view in the community is that it takes a bunch of excess energy to break apart the exciton, which meant that there had to be a large energy level difference between the donor and acceptor materials. But that big energy offset reduces the voltage of the solar cell. Our work dispels this perceived tradeoff in light of the impact that wavefunction delocalization and local crystallinity have on the charge separation process. This result should help people design new molecules and optimize donor and acceptor morphologies that help increase solar cell voltage without sacrificing current.”

The team used various luminescence and electroabsorption spectroscopic techniques together with X-ray diffraction to reach their conclusion. Their results, detailed in the paper titled “Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells,” will provide other groups with a better understanding of charge separation as they design and model more efficient organic solar cells.

Noel (Chris) Giebink is assistant professor of electrical engineering and a faculty member in the Materials Research Institute at Penn State. He can be contacted at ncg2@psu.edu.

Noel (Chris) Giebink | Newswise
Further information:
http://www.psu.edu

More articles from Power and Electrical Engineering:

nachricht A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes
20.07.2018 | Science China Press

nachricht Future electronic components to be printed like newspapers
20.07.2018 | Purdue University

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Future electronic components to be printed like newspapers

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes

20.07.2018 | Power and Electrical Engineering

Reversing cause and effect is no trouble for quantum computers

20.07.2018 | Information Technology

Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern

20.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>