The race is
on to commercialize photovoltaic cells made with conductive plastics.
startup announced last July that it had achieved a new world record for organic
photovoltaic (OPV) cell efficiency: 8.13 percent. On Nov. 29,
Massachusetts-based Konarka said it achieved an efficiency of 8.3 percent,
breaking the record.
The new OPV
records compare to 11 to 15 percent efficiency for traditional inorganic
silicon photovoltaic cells in converting sunlight to electricity. The maximum recorded
efficiency for crystalline silicon is 24.7 percent.
in efficiency in organic photovoltaics based on conductive plastics have been
slow in coming. Although organic photovoltaics have been around for 20 years,
they still represent close to zero percent of global energy production.
plastics are considered an important part of the world's energy future because
the cost of electricity from silicon photovoltaics is very high-roughly 10
times higher than fossil fuels such as coal and oil.
will be plenty of room for growth in several new photovoltaic technologies. In
2010, global cumulative installed photovoltaic (PV) capacity grew by 40
percent, with compounded annual growth forecast at 20 percent.
plastics offer these advantages:Better Designs.
Conductive plastics are flexible and
are easy to bond to flexible substrates such as plastic and metal foils, creating
opportunity for integrated, flexible applications. For example, mobile phones could
generate their own power.Costs.
Relatively inexpensive plastic is
used as the active material to convert solar energy into electricity. Only a
few tenths of a micrometer of conductive plastics are needed to generate
electricity. Printing capability.
Conductive solar cells can be printed
in processes similar to printing on newspaper. The fabrication process is described
as low temperature and environmentally friendly.
cells contain a light-sensitive semiconducting material that starts the process
of producing electricity. Today that material typically is silicon. OPVs
generally use two materials, one acting as a donor that captures electrons from
light (even indoor light) and the other acting as an electron acceptor. A
charge transfer process then begins, creating electricity.Climate change
discovery of pure conductive organic polymers (such as oxidized
iodine-doped polyacetylene) in the late twentieth century coupled with high petroleum prices
accelerated interest in OPVs. Concerns about climate change boosted research again
in OPVs in the last ten years. Solarmer Energy
of El Monte, CA announced
the efficiency record of 8.13 percent and in June 2010 the National Renewable
Energy Laboratory (NREL) and Solarmer signed a cooperative research and
development agreement to improve the lifetime of plastic solar cells.
be conducted with NREL's combinatorial degradation system, which compares the
performance of up to 360 OPV devices in parallel under simulated solar
conditions that accelerate the test results.
this collaboration we hope to improve plastic solar cell performance and extend
the cells' lifetime through the development of stable device architectures and
packaging systems," said NREL senior scientist Dana C. Olson, who is the
principal investigator on the collaboration project.
technology, which includes making electrically active plastics
colors, is representative of an explosion of research that is leading to
optimism about organic photovoltaics.
organic photovoltaics have been largely limited to charging consumer
electronics because of their short lifetimes, lasting only a couple years, and
low efficiencies (3 to 8 percent). One early application
is to provide power at poolside umbrellas for laptop recharging that cost
focusing on increasing the lifetime and efficiencies for organic photovoltaics.
Several companies hope to break the 10 percent efficiency barrier this year. Improving
stability may be farther off. Konica invests
global player is Konarka Technologies
spinoff of the University of Massachusetts Lowell. Last year Konica Minolta
invested $20 million in Konarka to further develop organic thin-film
3M Develops Solar Mirror Film
Conductive polymers are part of the solar energy picture for plastics. Here's a quick look at what's happening elsewhere:
- 3M's Renewable Energy division announced the commercial availability of its Solar Mirror Film 1100, a flexible, reflective film designed to provide a high-performance alternative to standard glass mirrors. It's 75 percent lighter than glass products and cuts overall costs by 20 percent. The film combines a weatherable acrylic front-side with silver as the reflective layer. It is coated with a pressure-sensitive adhesive on the backside complete with liner.
- BASF and Rhodia are providing customized grades of nylon for connectors and junction boxes of photovoltaic systems. Key features are flame resistance and high impact resistance at low temperatures.
- DuPont Circuit & Packaging Materials announced the commercial availability of Kapton polyimide films engineered for flexible photovoltaic substrates. New technologies are aimed at increasing the efficiency and lifetime of photovoltaic modules, and reducing overall system costs.
- Bayer Material Science is working on polycarbonate encapsulation films that can make it possible to produce flexible photovoltaic modules. Research is focusing on improvement of the product's barrier properties against oxygen and water, in order to protect the active layer.
- Sabic Innovative Plastics is focusing its R&D efforts on new back sheet materials that can replace metal to consolidate parts, reduce maintenance and simplify installation. Andy Verheijden, global product market leader, solar energy for SABIC Innovative Plastics, says: "For the future, we see a fully integrated system - with one molded part incorporating four functionalities: frame, junction box, connectors and back sheets. This is the beauty of designing in engineered thermoplastics."
- MIT chemical engineers have found a way to concentrate solar energy 100 times more than a regular photovoltaic cell through use of carbon nanotubes as antennas that capture and focus light energy, potentially allowing much smaller and more powerful solar arrays.
Minolta positions the organic thin-film photovoltaic business as one of the
most promising in the environment and energy field,next to the organic light-emitting
diode (OLED) business, where our photographic film manufacturing technology is
leading mass production," says Masatoshi Matsuzaki, CEO at Konica Minolta.
an attractive partner because of its commercial product, Power Plastic, which
is now being produced in a roll-to-roll process in New Bedford, MA. Power
Plastic captures indoor and outdoor light and converts it into direct current
(DC) electrical energy.
Plastic captures indoor and outdoor light and converts it into direct current
(DC) electrical energy. The technology traces its roots to development of a way
to process photovoltaic materials at relatively low temperatures, enabling the
use of low-costpolymers as the top and bottom surfaces of the photovoltaic
cell. The technology, invented by a team at UMASS Lowell, also enabled the
photovoltaic cells to be manufactured at high speed using coating and printing
At the heart of Konarka's technology is a
photo-reactive polymer invented by Konarka co-founder and Nobel Prize winner
AlanHeeger. This material can be printed or coated inexpensively onto flexible
applications for Power Plastic are coming from partners focused on
building-integrated photovoltaics (BIPV) and other shade and structure
applications. In one example, Arch Aluminum & Glass Co. is integrating
Power Plastic into a wall structure at Arch's office building in Tamarac, FL.
The solar panels will 1.5 kW of power to the facility.
of this project is to test the performance and robustness of our solar panel
solution for a curtain wall† application with a variety of glass and window
configurations under a wide range of environmental and insolation conditions,"says Terri Jordan, vice president of business development at Konarka. "The
yielded data and information will guide our development of the first-of-its-kind
vision application, a transparent, colored solar glass panel."
lifetime for Power Plastic is three-to-five years when exposed. If the
conductive layers are protected with glass or plastics, its lifetimes are
comparable to traditional solar cells.
companies are expected to establish a joint venture company
†in Japan to produce
organic thin-film photovoltaic panels.Ink systems
key product for the solar market is Plexcore PV, a ready-to-use ink system.
solar cells, sunlight is collected in the photoactive layer to create charge
carriers. When voltage is applied to the device, these carriers are separated
into positive and negative charges and then directed to the conductive
electrodes (cathode and transparent anode) to create power. A hole transport
layer improves extraction of positive charges from the photoactive ink by
matching of energy levels to photo-active ink.
efficiency is just shy of 7 percent," says Mary Boone, director of ink business
development for Plextronics. "From a goal perspective, we are targeting greater
than 8 percent efficiency in the next year." The technology is pre-commercial
and Plextronics provides inks in 50-liter batch sizes or less.
potential indoor application for the ink is point-of-purchase displays that
receive energy from fluorescent lighting.
†"Working with our partners and customers,
we've talked with major retailers and consumer goods companies in the U.S. who
want to replace the traditional paper signage used in stores today with
low-cost, animated point-of-purchase displays that are self-powered by OPV,"
says Boone. "Retailers don't want the ongoing cost and disruption of having to
purchase and replace conventional batteries in these displays, so there is
tremendous interest in using printable OPV as the power source for these new
recent development, Plextronics says it has improved low-temperature
processability of OPV. While previous industry standard techniques required a
glass substrate to be annealed at temperatures at or above 110C, the
proprietary method developed at Plextronics enables annealing at less than 65C.
This new method allows use of less-expensive substrates, especially once the
process is transferred to flexible substrates such as conventional plastic.
expect to introduce ink-jet printable inks for organic light-emitting diodes (OLED)
non-aqueous-based Hole Injection Layer (HIL) ink augments the company's
existing aqueous-based HIL, and is geared specifically for solution processable
phosphorescent OLED emitters.
plastic photovoltaic technology is close, but not yet part of the design
engineering toolbox on a practical level. But they may change in the next two
to five years.