Heralding a new era in the field of solar cell technology, Australian researchers have announced successful completion of trials to develop flexible, large area, cost-effective, reel-to-reel printable plastic solar cells. World leading research from CSIRO�s (Commonwealth Scientific and Industrial Research Organisation) Future Manufacturing Flagship suggest that the new technology employs a roll-to-roll mass manufacturing method for making thin-film plastic solar cells akin to the one employed to print Australian currency. The recently concluded solar cell printing trials formed a part of 3-year AU$12 mln Victorian Organic Solar Cell Consortium (VICOSC) and were carried out by Securency International, a banknote printing company.
The print trials conducted by CSIRO research team ran at 200 metres per minute, amounting to 100 kms/day under normal manufacturing conditions. According to the researchers, over a span of 5 months enough plastic solar cells could be printed to generate a gigawatt of power considering the cells achieve 10% efficiency. The printable solar cells address challenges faced by the traditional solar panel technology including the potential to mass produce the cells cheaply and install them over large areas with uneven surfaces due to their flexibility. As far as the mass production and cost effectiveness is concerned, the new technology holds a lot promise as the study is at vanguard of advanced polymer technology, which cheaply prints on a mass scale the banknotes used in Australia and 21 other such countries. The potential to manufacture cheaply and rapidly the flexible, organic solar cells which are �printed� on to polymer in this way holds a tremendous prospect for the future energy needs and requirements.
The CSIRO project aims to attain 10% conversion efficiency rate within 5 years with these flexible plastic solar cells; however, this is still far behind the �first generation� crystalline silicon modules which boast of electrical efficiency of 14-23% and an operating life of 20 years. Nevertheless, the advent of such printable, cheap, and roll-to-roll manufacturing processes and other �third generation� solar cell technologies are a step in the right direction to address the issues prevalent with c-Si modules which are too expensive for mass use, frail and require clean room special handling facilities. More than thirty years ago, the �first generation� silicon-wafer based solar cells were introduced which even capture the majority market share currently. Even though ground-breaking, this technology had issues of high cost, low capital efficiency and product cost/performance ratio. The process is very labor- and energy-intensive, with high manufacturing plant capital costs and limiting scale-up scope.
To address the challenge posed by high manufacturing and capital cost, a �second generation� technologies called thin film solar cells were developed. These technologies�either rigid or flexible--are typically made by depositing a thin layer of semiconductor photo-active material like amorphous silicon (a-Si), copper indium gallium diselenide (CIGS), or cadmium telluride (CdTe) on a glass, metal or a flexible plastic substrate like polyimide. These types also at times house one or two glass or plastics layers enclosing the semiconducting material. Out of the above semi-conducting material used for thin film solar cells, amorphous silicon, though cheaper than crystalline silicone, but is the most expensive relative to CIGS and CdTe.
One of the most promising development in the thin film cell technologies is the advent of breakthrough organic cells on plastic substrate which are characterized by continuous roll-to-roll manufacturing and cheaper than silicon wafer-based bulky solar cells and other thin film cells which employ a-Si, CIGS and CdTe layer as semi-conducting materials. Nevertheless, the only concern with organic thin film cells is the low conversion efficiency relative to other technologies. This is the area which is gaining interest amongst the research community to boost the efficiency while keep the cost of mass manufacturing low as possible. Konarka, Massachusetts-headquartered company uses nano-enabled polymer photovoltaic materials that are lightweight, flexible and more versatile than traditional solar materials. The company recently proclaimed a collaboration with French oil and petrochemicals major, Total. The French company is investing US$45 mln in Konarka, thereby becoming its biggest shareholder. Plextronics, another US-based company and a spinoff from Carnegie Mellon University is also involved in plastic solar cell technology. Plextronics uses conductive polymer technology developed by Dr. Richard McCullough of Carnegie Mellon University.
Konarka Technologies, Inc., a developer of Power Plastic�, a flexible material that converts light to energy, announced late last year that the National Energy Renewable Laboratory (NREL) has verified that the flexible organic based photovoltaic (PV) solar cells has demonstrated 6% efficiency performance. The results were achieved by Dr. Alan Heeger of the University of California, Santa Barbara, and chief scientist at Konarka, under the scope of the Sustainable Development Technology Canada program (SDTC), which provides funding to partners for the development of low cost printable organic solar cells. Konarka is the U.S. industrial solar cell partner for the program and has collaborated with the Universit� Laval, the National Research Council of Canada and Saint Jean Photochimie for the past four years. The company last year obtained the exclusive license for a new family of photoactive polymers (polycarbazoles - PCZ) originally developed by Professor Mario Leclerc, director of the Macromolecular Science and Engineering Research Center of Universit� Laval (CERSIM) and director of the Quebec Center on Functional Materials (CQMF), and jointly developed for solar cell application by the SDTC consortium. Accordingly, Dr. Alan Heeger integrated the material into his cell architecture and has advanced the performance, as verified by the National Renewable Energy Laboratory (NREL). The target of the consortium is to develop solar cells with efficiencies in excess of 10%. Konarka scientists are conducting advanced research in power fibers, bi-facial cells, and tandem architectures that could substantially raise conversion efficiency and open new markets.
At the core of Konarka�s technology is its active photovoltaic material that is made from semi-conducting polymers and nano-engineered materials i.e. ink containing fullerene conductive nano-carbon clusters. The printed active material absorbs photons to trigger the release of electrons which are then transported to create electricity. The active material is sandwiched between printed electrodes which are sandwiched between the substrate and the transparent packaging material. The substrate is any plastic that can be metallized in a web process, polyester being a preferred material. Besides, other plastics like polycarbonate, acrylic and polystyrene can be used. Konarka�s proprietary photo-reactive materials 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. An assessment of company�s patents indicates that a large amount of work involves conjugated polymers that act as metallic conductors and semiconductors. The process is non-toxic and environmentally friendly, and because it�s conducted at low temperatures, is less energy intensive than 1st or 2nd generation technologies. Another significant advantage is that it can be produced using existing coating and printing equipment, and thus does not require construction of a new facility. Konarka�s Power Plastic� is inexpensive (5 times less than traditional solar), lightweight (1-2 oz/ft2, 25-50g/m2) versatile (can be colored, patterned and cut-to-fit), and flexible (easily adapted to an application�s form factor).
Konarka�s technology enables integration into multiple application channels including portable devices, such as mobile phones, PDAs, digital music players, and laptops; architectural materials, such as rooftops, siding, window panes, blinds, and awnings; sensor networks; and fabrics, such as jackets and handbags that can charge portable devices. The company has also successfully demonstrated its portable and structural applications through partnerships with the US military. Going by the number of research funded in development of cheap, highly efficient, mass-manufactured flexible solar cells on plastic, these projects have tremendous prospects for solving energy needs and issues of the future.