Featured Research

from universities, journals, and other organizations

New understanding could result in more efficient organic solar cells

Date:
February 3, 2014
Source:
Penn State Materials Research Institute
Summary:
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 new paper. The research suggests design rules for making more efficient solar cells in the future.

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

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.

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.


Story Source:

The above story is based on materials provided by Penn State Materials Research Institute. Note: Materials may be edited for content and length.


Journal Reference:

  1. B. Bernardo, D. Cheyns, B. Verreet, R.D. Schaller, B.P. Rand, N.C. Giebink. Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells. Nature Communications, 2014; 5 DOI: 10.1038/ncomms4245

Cite This Page:

Penn State Materials Research Institute. "New understanding could result in more efficient organic solar cells." ScienceDaily. ScienceDaily, 3 February 2014. <www.sciencedaily.com/releases/2014/02/140203155048.htm>.
Penn State Materials Research Institute. (2014, February 3). New understanding could result in more efficient organic solar cells. ScienceDaily. Retrieved April 19, 2014 from www.sciencedaily.com/releases/2014/02/140203155048.htm
Penn State Materials Research Institute. "New understanding could result in more efficient organic solar cells." ScienceDaily. www.sciencedaily.com/releases/2014/02/140203155048.htm (accessed April 19, 2014).

Share This



More Matter & Energy News

Saturday, April 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Small Reactors Could Be Future of Nuclear Energy

Small Reactors Could Be Future of Nuclear Energy

AP (Apr. 17, 2014) After the Fukushima nuclear disaster, the industry fell under intense scrutiny. Now, small underground nuclear power plants are being considered as the possible future of the nuclear energy. (April 17) Video provided by AP
Powered by NewsLook.com
Horseless Carriage Introduced at NY Auto Show

Horseless Carriage Introduced at NY Auto Show

AP (Apr. 17, 2014) An electric car that proponents hope will replace horse-drawn carriages in New York City has also been revealed at the auto show. (Apr. 17) Video provided by AP
Powered by NewsLook.com
Honda's New ASIMO Robot, More Human-Like Than Ever

Honda's New ASIMO Robot, More Human-Like Than Ever

AFP (Apr. 17, 2014) It walks and runs, even up and down stairs. It can open a bottle and serve a drink, and politely tries to shake hands with a stranger. Meet the latest ASIMO, Honda's humanoid robot. Duration: 00:54 Video provided by AFP
Powered by NewsLook.com
German Researchers Crack Samsung's Fingerprint Scanner

German Researchers Crack Samsung's Fingerprint Scanner

Newsy (Apr. 16, 2014) German researchers have used a fake fingerprint made from glue to bypass the fingerprint security system on Samsung's new Galaxy S5 smartphone. Video provided by Newsy
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:
from the past week

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