Although the photovoltaic market has seen a rapid increase driven by technology and environmental concern, some statistics show that solar cells still only contribute less than 0.1% of our electricity needs. The underlying reason is cost and materials scalability.
First generation wafer-based silicon solar technology is limited by polysilicon feedstock and high cost of manufacturing. Second generation thin-film inorganic solar technology is still not cost competitive, and the popular materials used, like Cadmium and Indium, are toxic, expensive, and not scalable to meet global demand. Even with materials and manufacturing cost reduction, the second-generation thin-film industry is affected by the heavy glass substrates required.
Future generation organic photovoltaic (OPV) technology has the promise to be the low-cost renewable energy solution. The most attractive potential of OPVs is the capability for high-speed manufacturing in roll-to-roll coating and/or printing production. In addition, OPVs are light-weight, thin, and flexible to significantly reduce balance of systems costs and enable solar cells to be placed anywhere.
A great deal of time and research has gone into the development of OPVs.
A recent breakthrough was made by Mitsubishi Cooperation (MC), the National Institute of Advanced Industrial Science and Technology (AIST) and Tokki Corporation (TOKKI) who have succeeded in developing what they believe to be the world's first highly-integrated Organic Photovoltaics (OPV) module.
The new module uses laser-scribing technology on a glass substrate. Organic semiconductor materials are deposited on the substrate and then divided into several cells with the laser. The technology eliminates the need for, deposition mask patterning, which is used in conventional methods. The new module is highly integrated and should improve sunlight conversion efficiency.
OPVs are expected to be used in windows, walls, cloths, textiles, outdoor equipment and toys. These applications have proven difficult for the silicon type of PV modules currently in use, and the hope is that OPVs will be more effective. Until now, however, the efficiency of OPVs in converting sunlight has been a problem. MC, AIST and TOKKI now believe they have developed a highly-integrated technology to solve this problem.
The National Energy Renewable Laboratory (NREL) certified last month that Konarka's OPV solar cells have demonstrated 6.4% efficiency. This is the highest performance recorded by NREL for an organic photovoltaic solar cell.
At the heart of Konarka's technology is a photo-reactive polymer material, which can be printed or coated inexpensively onto flexible substrates using roll-to-roll manufacturing, similar to the way newspaper is printed on large rolls of paper.
The company does not currently create consumer applications but makes a light-sensitive material (Power Plastic) that other manufacturers can integrate into their products to turn them into energy-capturing devices. This could include shade structures which will power personal electronic devices anywhere the sun is shining; carport covers which will trickle charge an electric car; emergency power generators, which will enable police, military and emergency personnel to maintain vital communications and much more.
Solarmer recently announced that for 2009, they would focus on commercializing and manufacturing their low-cost, lightweight, flexible solar panels that use organic materials. They will start by making samples of these panels available to potential customers beginning this September.
Dr. Vishal Shrotriya, Director of Product and Business Development, says, "Our ability to have prototypes available in such a short time shows the capability of our Research and Development department. I'm sure our manufacturing process will soon follow suit."
The company's pilot line target completion date is March 2010. These panels will create new markets that are currently not addressable with conventional silicon solar panel technology. The first major applications for this technology will likely be portable digital electronic devices (such as cell phones and laptops) and outdoor lifestyle applications. Smart Fabrics and Building-Integrated Photovoltaics will soon follow.
Intel are also looking at power conversion efficiency of OPV devices in a project that focuses on new materials design for greater solar energy absorption and on improving device geometry with ordered nano-fabrication of the OPV layer. The project seeks to increase efficiency, scalability, and stability of OPVs through proper materials design and device engineering.
Yuri Sylvester, research scientist with Intel Labs in Seattle, was reported as saying that Intel has been working on the organic photovoltaic problem for some time. He sees the technology as holding promise, since it involves cheaply made materials that can withstand small impurities - no more clean rooms required for production. Organic dyes and inks can also be inexpensively laid on flexible substances like plastic, potentially opening up solar power to a whole new class of uses.
He said the main problem with the technology is that the dyes or inks that convert sunlight into electricity lose their efficiency when applied at greater than laboratory scales. For example, Intel has achieved a 6 percent efficiency in converting sunlight to electricity in tiny lab-made cells but increasing them to practical sizes drops that efficiency down to about 2 percent.
New Energy Technologies Inc
In a recent series of new experiments, researchers at New Energy Technologies Inc repeatedly tested their ultra-small solar cells on a 1"x1" substrate against today's popular solar materials for their capacity to produce electricity under varying artificial light conditions, mimicking the levels of light exposure in homes and commercial offices. In every case, New Energy claims their solar cells, the smallest reported organic solar cells of their kind in the world, exponentially outperformed all of the conventional materials tested.
Researchers Apply Coating to Commercial Glass, Demonstrating Transparency of New Energy's SolarWindow™ Capable of Generating Electricity, Currently Under Development (Source: New Energy Technologies).
Under normal office lighting conditions, without the benefit of outside natural light from windows, the solar cells produced:
- Almost 2-fold greater output power density than monocrystalline silicon, an established commercial solar cell material;
- More than 8-fold greater output power density than copper-indium-selenide, known for its high optical absorption coefficients and versatile optical and electrical characteristics; and
- More than 10-fold greater output power density than flexible thin-film amorphous-silicon, a popular 'second-generation' solar thin-film material.
The solar cells generate electricity not only from the visible radiation found in sunlight but also by using the visible light found in artificial illumination, such as the fluorescent lighting typically installed in offices and commercial buildings.
New Energy's SolarWindow™ technology makes use of an organic solar array, which has the same desirable electrical properties as silicon, yet has a considerably better capacity to 'optically absorb' photons from light to generate electricity and achieves transparency through the innovative use of conducting polymers. Each solar array is composed of a series of twenty ultra-small solar cells measuring less than ¼ the size of a grain of rice each. The organic solar cells are fabricated using environmentally-friendly hydrogen-carbon based materials, and successfully produce electricity.
For more attend Photovoltaics Beyond Conventional Silicon USA 2009 Dec 2-3, San Jose, USA.