Featured Research

from universities, journals, and other organizations

Cheap, Plastic Solar Cells May Be On The Horizon, Thanks To New Technology Developed By UC Berkeley, LBNL Chemists

Date:
April 4, 2002
Source:
University Of California - Berkeley
Summary:
University of California, Berkeley, chemists have found a way to make cheap plastic solar cells flexible enough to paint onto any surface and potentially able to provide electricity for wearable electronics or other low-power devices.

Berkeley - University of California, Berkeley, chemists have found a way to make cheap plastic solar cells flexible enough to paint onto any surface and potentially able to provide electricity for wearable electronics or other low-power devices.

The group's first crude solar cells have achieved efficiencies of 1.7 percent, far less than the 10 percent efficiencies of today's standard commercial photovoltaics. The best solar cells, which are very expensive semiconductor laminates, convert, at most, 35 percent of the sun's energy into electricity.

"Our efficiency is not good enough yet by about a factor of 10, but this technology has the potential to do a lot better," said A. Paul Alivisatos, professor of chemistry at UC Berkeley and a member of the Materials Science Division of Lawrence Berkeley National Laboratory. "There is a pretty clear path for us to take to make this perform much better."

Alivisatos and his co-authors, graduate student Wendy U. Huynh and post-doctoral fellow Janke J. Dittmer, report their development in the March 29 issue of Science.

"The beauty of this is that you could put solar cells directly on plastic, which has unlimited flexibility," Dittmer said. "This opens up all sorts of new applications, like putting solar cells on clothing to power LEDs, radios or small computer processors."

The solar cell they have created is actually a hybrid, comprised of tiny nanorods dispersed in an organic polymer or plastic. A layer only 200 nanometers thick is sandwiched between electrodes, and can produce, at present, about 0.7 volts. The electrode layers and nanorod/polymer layers could be applied in separate coats, making production fairly easy. And unlike today's semiconductor-based photovoltaic devices, plastic solar cells can be manufactured in solution in a beaker without the need for clean rooms or vacuum chambers.

"Today's high-efficiency solar cells require very sophisticated processing inside a clean room and complex engineering to make the semiconductor sandwiches," Alivisatos said. "And because they are baked inside a vacuum chamber, they have to be made relatively small."

The team's process for making hybrid plastic solar cells involves none of this.

"We use a much dirtier process that makes it cheap," Huynh said.

The technology takes advantage of recent advances in nanotechnology, specifically the production of nanocrystals and nanorods pioneered by Alivisatos and his laboratory colleagues. These are chemically pure clusters of from 100 to 100,000 atoms with dimensions on the order of a nanometer, or a billionth of a meter. Because of their small size, they exhibit unusual and interesting properties governed by quantum mechanics, such as the absorption of different colors of light depending upon their size.

It was only two years ago that a UC Berkeley team led by Alivisatos found a way to make nanorods of a reliable size out of cadmium selenide, a semiconducting material. Conventional semiconductor solar cells are made of polycrystalline silicon or, in the case of the highest efficiency ones, crystalline gallium arsenide.

Huynh and Dittmer manufactured nanorods in a beaker containing cadmium selenide, aiming for rods of a diameter - 7 nanometers - to absorb as much sunlight as possible. They also aimed for nanorods as long as possible - in this case, 60 nanometers. They then mixed the nanorods with a plastic semiconductor, called P3HT - poly-(3-hexylthiophene) - and coated a transparent electrode with the mixture. The thickness, 200 nanometers - a thousandth the thickness of a human hair - is a factor of 10 less than the micron-thickness of semiconductor solar cells. An aluminum coating acting as the back electrode completed the device.

The nanorods act like wires. When they absorb light of a specific wavelength, they generate an electron plus an electron hole - a vacancy in the crystal that moves around just like an electron. The electron travels the length of the rod until it is collected by the aluminum electrode. The hole is transferred to the plastic, which is known as a hole-carrier, and conveyed to the electrode, creating a current.

P3HT and similar plastic semiconductors currently are a hot area of research in solar cell technology, but by themselves these plastics are lucky to achieve light-conversion efficiencies of several percent.

"All solar cells using plastic semiconductors have been stuck at two percent efficiency, but we have that much at the beginning of our research," Huynh said. "I think we can do so much better than plastic electronics."

"The advantage of hybrid materials consisting of inorganic semiconductors and organic polymers is that potentially you get the best of both worlds," Dittmer added. "Inorganic semiconductors offer excellent, well-established electronic properties and they are very well suited as solar cell materials. Polymers offer the advantage of solution processing at room temperature, which is cheaper and allows for using fully flexible substrates, such as plastics."

Visiting scientist Keith Barnham, professor of physics at Imperial College, London, and an expert on high-efficiency solar cells, agreed.

"This is exciting, cheap technology if they can get the efficiency up to 10 percent, which I think they will, in time," Barnham said. "Paul's approach is a very promising way to get around the problem of the efficiency of plastic solar cells."

Some of the obvious improvements include better light collection and concentration, which already are employed in commercial solar cells. But Alivisatos and his colleagues hope to make significant improvements in the plastic/nanorod mix, too, ideally packing the nanorods closer together, perpendicular to the electrodes, using minimal polymer, or even none - the nanorods would transfer their electrons more directly to the electrode. In their first-generation solar cells, the nanorods are jumbled up in the polymer, leading to losses of current via electron-hole recombination and thus lower efficiency.

They also hope to tune the nanorods to absorb different colors to span the spectrum of sunlight. An eventual solar cell might have three layers, each made of nanorods that absorb at different wavelengths.

"For this to really find widespread use, we will have to get up to around 10 percent efficiency," Alivisatos said. "But we think it's very doable."

The work was funded by the National Renewable Energy Laboratory and the Department of Energy.


Story Source:

The above story is based on materials provided by University Of California - Berkeley. Note: Materials may be edited for content and length.


Cite This Page:

University Of California - Berkeley. "Cheap, Plastic Solar Cells May Be On The Horizon, Thanks To New Technology Developed By UC Berkeley, LBNL Chemists." ScienceDaily. ScienceDaily, 4 April 2002. <www.sciencedaily.com/releases/2002/04/020402073707.htm>.
University Of California - Berkeley. (2002, April 4). Cheap, Plastic Solar Cells May Be On The Horizon, Thanks To New Technology Developed By UC Berkeley, LBNL Chemists. ScienceDaily. Retrieved September 21, 2014 from www.sciencedaily.com/releases/2002/04/020402073707.htm
University Of California - Berkeley. "Cheap, Plastic Solar Cells May Be On The Horizon, Thanks To New Technology Developed By UC Berkeley, LBNL Chemists." ScienceDaily. www.sciencedaily.com/releases/2002/04/020402073707.htm (accessed September 21, 2014).

Share This



More Matter & Energy News

Sunday, September 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

What This MIT Sensor Could Mean For The Future Of Robotics

What This MIT Sensor Could Mean For The Future Of Robotics

Newsy (Sep. 20, 2014) MIT researchers developed a light-based sensor that gives robots 100 times the sensitivity of a human finger, allowing for "unprecedented dexterity." Video provided by Newsy
Powered by NewsLook.com
MIT BioSuit A New Take On Traditional Spacesuits

MIT BioSuit A New Take On Traditional Spacesuits

Newsy (Sep. 19, 2014) The MIT BioSuit could be an alternative to big, bulky traditional spacesuits, but the concept needs some work. Video provided by Newsy
Powered by NewsLook.com
New Music With Recycled Instruments at Colombia Fest

New Music With Recycled Instruments at Colombia Fest

AFP (Sep. 19, 2014) Jars, bottles, caps and even a pizza box, recovered from the trash, were the elements used by four musical groups at the "RSFEST2014 Sonorities Recycling Festival", in Colombian city of Cali. Duration: 00:49 Video provided by AFP
Powered by NewsLook.com
Virtual Reality Headsets Unveiled at Tokyo Game Show

Virtual Reality Headsets Unveiled at Tokyo Game Show

AFP (Sep. 18, 2014) Several companies unveiled virtual reality headsets at the Tokyo Game Show, Asia's largest digital entertainment exhibition. Duration: 00:48 Video provided by AFP
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