Featured Research

from universities, journals, and other organizations

Taking the pulse of charge-separation processes: Self-organization gives rise to more efficient organic solar cells

Date:
October 25, 2011
Source:
Ludwig-Maximilians-Universitaet Muenchen (LMU)
Summary:
Organic solar cells have the potential to convert sunlight into electrical energy in an economical and environmentally friendly fashion. The challenge is that they still work less efficiently than inorganic semiconductors. Ultrafast measurements on hybrid cells now reveal a route to double their efficiency.

Organic solar cells have the potential to convert sunlight into electrical energy in an economical and environmentally friendly fashion. The challenge is that they still work less efficiently than inorganic semiconductors. Ultrafast measurements on hybrid cells now reveal a route to double their efficiency.

Related Articles


The use of organic photovoltaics for the production of electricity from sunlight offers an attractive and promising basis for an innovative and environmentally friendly means of energy supply. They can be manufactured quite economically and, because they are as bendable as plastic wrap, they can be processed flexibly. The problem is that they are yet markedly less efficient than conventional inorganic semiconductor cells.

The most crucial process in the conversion of light into electric current is the generation of free charge carriers. In the first step of photoconversion, upon absorption of light one component of the organic solar cell, usually a polymer, releases electrons that are taken up by the second component of the cell -- in this case silicon nanoparticles -- and can then be transported further.

"The mechanisms and the timescale of charge separation have been the subject of controversial scientific debate for many years," says LMU physics professor Eberhard Riedle. In cooperation with investigators at the Technical University in Munich and at Bayreuth University, Riedle and his group have now been able to dissect the process in detail. To do so, the researchers used a novel hybrid cell type containing both organic and inorganic constituents, in which silicon serves as the electron acceptor. Based on the insights obtained with this system, they developed a processing strategy to improve the structural order of the polymer -- and found that this enhances the efficiency of charge separation in organic semiconductors by up to twofold. Their findings provide a new way to optimize the performance of organic solar cells.

The key to this breakthrough lies in a unique, laser-based experimental setup, which combines extremely high temporal resolution of 40 femtoseconds (fs) with a very broadband detection. This allowed the team to follow the ultrafast processes induced by photon absorption in real time as they occur. Instead of the fullerenes used in typical organic cells, the researchers used silicon as the electron acceptor, a choice that has two major advantages.

"First, with these novel hybrid solar cells, we were able to probe the photophysical processes taking place in the polymer with greater precision than ever before, and secondly through the use of silicon, a much larger segment of the solar spectrum can be harnessed for electricity," says Riedle. It turns out that free charge carriers -- so called polarons -- are not generated immediately upon photoexcitation, but with a delay of about 140 fs. Primary photoexcitation of a polymer molecule first leads to the formation of an excited state, called an exciton. This then dissociates, releasing an electron, which is then transferred to the electron acceptor.

The loss of electrons leaves behind positively charged "holes" in the polymer and, as oppositely charged entities are attracted to one another by the Coulomb force, the two have a tendency to recombine. "In order to obtain free charge carriers, electron and hole must both be sufficiently mobile to overcome the Coulomb force," explains Daniel Herrmann, the first author of the new study. The team was able to show, for the first time, that this is much easier to achieve in polymers with an ordered, regular structure than with polymers that are chaotically arranged. In other words, a high degree of self-organization of the polymer significantly increases the efficiency of charge separation.

"The polymer that we used is one of the few known to have a tendency to self-organize. This tendency can be inhibited, but one can also increase the polymer's intrinsic propensity for self-organization by choosing appropriate processing parameters," Herrmann explains. By cleverly optimizing the processing of the polymer P3HT, the researchers succeeded in doubling the yield of free charge carriers -- and thereby significantly enhancing the efficiency of their experimental solar cells.


Story Source:

The above story is based on materials provided by Ludwig-Maximilians-Universitaet Muenchen (LMU). Note: Materials may be edited for content and length.


Journal Reference:

  1. Daniel Herrmann, Sabrina Niesar, Christina Scharsich, Anna Kφhler, Martin Stutzmann, Eberhard Riedle. Role of Structural Order and Excess Energy on Ultrafast Free Charge Generation in Hybrid Polythiophene/Si Photovoltaics Probed in Real Time by Near-Infrared Broadband Transient Absorption. Journal of the American Chemical Society, 2011; 111021142308005 DOI: 10.1021/ja207887q

Cite This Page:

Ludwig-Maximilians-Universitaet Muenchen (LMU). "Taking the pulse of charge-separation processes: Self-organization gives rise to more efficient organic solar cells." ScienceDaily. ScienceDaily, 25 October 2011. <www.sciencedaily.com/releases/2011/10/111024101450.htm>.
Ludwig-Maximilians-Universitaet Muenchen (LMU). (2011, October 25). Taking the pulse of charge-separation processes: Self-organization gives rise to more efficient organic solar cells. ScienceDaily. Retrieved October 24, 2014 from www.sciencedaily.com/releases/2011/10/111024101450.htm
Ludwig-Maximilians-Universitaet Muenchen (LMU). "Taking the pulse of charge-separation processes: Self-organization gives rise to more efficient organic solar cells." ScienceDaily. www.sciencedaily.com/releases/2011/10/111024101450.htm (accessed October 24, 2014).

Share This



More Matter & Energy News

Friday, October 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

3D Printed Instruments Make Sweet Music in Sweden

3D Printed Instruments Make Sweet Music in Sweden

Reuters - Innovations Video Online (Oct. 23, 2014) — Students from Lund University's Malmo Academy of Music are believed to be the world's first band to all use 3D printed instruments. The guitar, bass guitar, keyboard and drums were built by Olaf Diegel, professor of product development, who says 3D printing allows musicians to design an instrument to their exact specifications. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Chameleon Camouflage to Give Tanks Cloaking Capabilities

Chameleon Camouflage to Give Tanks Cloaking Capabilities

Reuters - Innovations Video Online (Oct. 22, 2014) — Inspired by the way a chameleon changes its colour to disguise itself; scientists in Poland want to replace traditional camouflage paint with thousands of electrochromic plates that will continuously change colour to blend with its surroundings. The first PL-01 concept tank prototype will be tested within a few years, with scientists predicting that a similar technology could even be woven into the fabric of a soldiers' clothing making them virtually invisible to the naked eye. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Jet Sales Lift Boeing Profit 18 Pct.

Jet Sales Lift Boeing Profit 18 Pct.

Reuters - Business Video Online (Oct. 22, 2014) — Strong jet demand has pushed Boeing to raise its profit forecast for the third time, but analysts were disappointed by its small cash flow. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Internet of Things Aims to Smarten Your Life

Internet of Things Aims to Smarten Your Life

AP (Oct. 22, 2014) — As more and more Bluetooth-enabled devices are reaching consumers, developers are busy connecting them together as part of the Internet of Things. (Oct. 22) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins