Subscribe free to our newsletters via your
. Space Travel News .




SOLAR DAILY
A more efficient, lightweight and low-cost organic solar cell
by Staff Writers
Amherst MA (SPX) Sep 23, 2014


Illustration only.

For decades, polymer scientists and synthetic chemists working to improve the power conversion efficiency of organic solar cells were hampered by the inherent drawbacks of commonly used metal electrodes, including their instability and susceptibility to oxidation.

Now for the first time, researchers at the University of Massachusetts Amherst have developed a more efficient, easily processable and lightweight solar cell that can use virtually any metal for the electrode, effectively breaking the "electrode barrier."

This barrier has been a big problem for a long time, says UMass Amherst's Thomas Russell, professor of polymer science and engineering. "The sun produces 7,000 times more energy per day than we can use, but we can't harness it well.

One reason is the trade-off between oxidative stability and the work function of the metal cathode." Work function relates to the level of difficulty electrons face as they transfer from the solar cell's photoactive layer to the electrode delivering power to a device.

Russell likes to use a lock-and-dam analogy to talk about electron transfer. "People have thought you'd need to use tricks to help electrons, the water in the lock, over an obstacle, the electrode, like a dam. Tricks like sawing the dam apart to allow the flow. But tricks are always messy, introducing a lot of stuff you don't need," he says.

"The beauty of the solution reached by these synthetic chemists is to just move the dam out of the way, electronically move it so there is no longer a difference in energy level."

Synthetic chemist and polymer science professor Todd Emrick agrees, "That challenge was unmet and that's what this research is all about."

He and polymer chemistry doctoral student Zak Page in his lab had been synthesizing new polymers with zwitterions on them, applying them to several different polymer scaffolds in conjugated systems, also known as semiconductors, in the inter-layer of solar cells. Zwitterions are neutral molecules with both a positive and negative charge that also have strong dipoles that interact strongly with metal electrodes, the scientists found.

Emrick asked Page to see if he could synthesize conjugated polymers, semiconductors, with zwitterionic functionality. With time, and by enlisting a system of multiple solvents including water, Page was able to prepare these new "conjugated polymer zwitterions," or CPZs.

Emrick explains, "Once we could make CPZs, we were able to incorporate any conjugated backbone we wanted with zwitterionic functionality. That allowed us to make a library of CPZs and look at their structure-property relationship to understand which would be most important in electronics. In particular, we were interested in electron transport efficiency and how well the CPZ could modify the work function of different metals to help move electons across interfaces towards more powerful devices.

In choosing a metal for use as an electrode, scientists must always negotiate a trade-off, Page says. More stable metals that don't degrade in the presence of water and oxygen have high work function, not allowing good electron transport. But metals with lower work function (easier electron transport) are not stable and over time will degrade, becoming less conductive.

Guided by UMass Amherst's photovoltaic facility director Volodimyr Duzhko in using ultraviolet photoelectron spectroscopy (UPS), Page began to categorize several metals including copper, silver and gold, to identify exactly what aided electron transport from the photoactive layer to the electrode.

He and Emrick found that "if you want to improve the interlayer properties, you have to make the interface layer extremely thin, less than 5 nanometers, which from a manufacturing standpoint is a problem," he says.

To get around this, Page and Emrick began to consider a classic system known for its good electron transport: buckyballs, or fullerenes, often used in the photoactive layer of solar cells.

"We modified buckyballs with zwitterions (C60-SB) to change the work function of the electrodes, and we knew how to do that because we had already done it with polymers," Page points out. "We learned how to incorporate zwitterion functionality into a buckyball as efficiently as possible, in three simple steps."

Here the synthetic chemists turned to Russell's postdoctoral researcher Yao Liu, giving him two different fullerene layers to test for electron transfer efficiency: C60-SB and another with amine components, C60-N. From UPS analysis of the zwitterion fullerene precursor, Page suspected that the amine type would enhance power even better the C60-SB variety. Indeed, Liu found that a thin layer of C60-N between the solar cell's photoactive layer and the electrode worked best, and the layer did not have to be ultra-thin to function effectively, giving this discovery practical advantages.

"That's when we knew we had something special," says Page. Emrick adds, "This is really a sweeping change in our ability to move electrons across dissimilar materials. What Zak did is to make polymers and fullerenes that change the qualities of the metals they contact, that change their electronic properties, which in turn transforms them from inefficient to more efficient devices than had been made before."

Russell adds, "Their solution is elegant, their thinking is elegant and it's really easy and clean. You put this little layer on there, it doesn't matter what you put on top, you can use robust metals that don't oxidize. I think it's going to be very important to a lot of different scientific communities."

.


Related Links
University of Massachusetts at Amherst
All About Solar Energy at SolarDaily.com






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





SOLAR DAILY
TUV Offers Fire Testing Services Per Latest UL 1703 Specs
Tempe AZ (SPX) Sep 17, 2014
TUV Rheinland offers the UL 1703 testing and certification services to manufacturers of building integrated photovoltaic modules (BiPV), rack-mounted photovoltaic (PV) modules and mounting systems in conjunction with the 2014 revision of the standard, which introduces new PV module fire type classification and system rating tests. Effective January 1, 2015, rooftop mounted systems in Calif ... read more


SOLAR DAILY
Elon Musk gets fresh challenge with space contract

Proton Launches May Compete on Price With US Falcons

NASA's Wind-Watching ISS-RapidScat Ready for Launch

SpaceX's next cargo launch set for Sept 20

SOLAR DAILY
NASA Mars Spacecraft Ready for Sept. 21 Orbit Insertion

India A New Contender in Asian Space Race or Technological Breakthrough

MAVEN on course for Mars Arrival Sept 21

NASA spacecraft to begin orbiting Mars within days

SOLAR DAILY
Year's final supermoon is a Harvest Moon

China Aims for the Moon, Plans to Bring Back Lunar Soil

Electric Sparks May Alter Evolution of Lunar Soil

China to test recoverable moon orbiter

SOLAR DAILY
Awaiting New Results on Pluto's Atmosphere

New Horizons Crosses Neptune Orbit On Route To First Pluto Flyby

From Pinpoint of Light to a Geologic World

New Horizons Spies Charon Orbiting Pluto

SOLAR DAILY
Chandra Finds Planet That Makes Star Act Deceptively Old

Solar System Simulation Reveals Planetary Mystery

'Hot Jupiters' provoke their own host suns to wobble

First evidence for water ice clouds found outside solar system

SOLAR DAILY
Boeing, SpaceX to send astronauts to space station

Space Launch System Will Use Massive Welding Tool

Europe readies 'space plane' for sub-orbital test flight

World's Largest Spacecraft Welding Tool for Space Launch System Completed

SOLAR DAILY
Astronauts eye China's future space station

China eyes working with other nations as station plans develop

China completes construction of advanced space launch facility

China to launch second space lab in 2016: official

SOLAR DAILY
Dawn Operating Normally After Safe Mode Triggered

'J' marks the spot for Rosetta's lander

'J' marks the spot for historic comet landing

A Map of Rosetta's Comet




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.