Towards the Next Generation of Ultra-low-cost Photovoltaics Using Nanocrystal Inks
a report by
Vahid A Akhavan, Brian W Goodfellow, Matthew G Panthani and Brian A Korgel Department of Chemical Engineering, Texas Materials Institute, and Center for Nano- and Molecular Science and Technology, University of Texas at Austin
The average price of solar power is now US$0.29/kWh,1,2 which is
about three times higher than the retail cost of electricity in the US.3 Currently, more than 50% of the total cost of photovoltaic (PV) electricity is associated with the price of the module, and grid parity requires significant reductions in solar cell manufacturing costs. The solar cell market is dominated by crystalline silicon-based modules4 and, since 2004, the cost of these modules has decreased by only 5%.4
and because the cost of the raw because very
organic light-absorbing materials have been made – so-called organic photovoltaics (OPVs) – with efficiencies as high as 7.4%.9
commercial viability, the device efficiency must still be improved and the relatively high materials costs of these devices need to be addressed. In addition, there is a concern about long-term OPV device stability under typical operating conditions in the field.
Significant price reductions for crystalline silicon-based solar cells have been slow both because it is a relatively mature technology with largely optimised device efficiency1,5
materials is significant. The cost of silicon alone contributes as much as 50% of the module cost and 28% of the total cost1
thick silicon layers of more than 500µm are needed (silicon is a very inefficient light absorber) and the competition for highly purified electronic-grade silicon with the microelectronics industry keeps the price of silicon high.6
Alternatives to Silicon
A ‘second generation’ of silicon-alternative PV technologies that use thin absorber layers has been developed utilising materials such as amorphous silicon, CdTe and copper indium gallium selenide (CIGS).7 The efficiency of these devices is not quite as high as that of devices using crystalline silicon, but the manufacturing costs are significantly lower. The cost of solar power depends roughly on the ratio of the efficiency to the manufacturing and installation costs, making these technologies competitive with silicon, and they now account for about one-quarter of the PV market share.4
First Solar’s new CdTe PV
technology has recently been reported with a module sale price of only US$0.98/Wp,8
just below the US$1/Wp level that many considered the target for grid parity.
However, the manufacturing processes for these silicon alternatives are still relatively slow and expensive, requiring high-temperature processing steps that make an order of magnitude reduction in manufacturing cost unlikely. New approaches with the potential for dramatic reductions in cost are desired.
Third-generation Photovoltaics and the Printed Inorganic Thin-film Solar Cell
To date, a materials system and processing approach with the potential for both high efficiency and ultra-low-cost has not been identified. Such a technology would most likely need to be compatible with high-throughput roll-to-roll deposition and inexpensive plastic, flexible and lightweight substrates. The ‘third-generation’ PV devices would yield efficiencies above 10%, as needed for commercial viability, but with dramatically reduced manufacturing costs.7
One target has been to create a technology for fabricating plastic disposable solar cells. As a step in this direction, PV devices made from
© TOUCH BRIEFINGS 2010
Vahid A Akhavan is a PhD candidate and Engineering Graduate Research Assistant at the University of Texas at Austin. His research focuses on the production of photovoltaic devices from colloidal nanoparticles and investigating how the electronic behaviour of nanoparticulate films differs from that of bulk properties. He received his BSc from the Chemical Engineering Department at The University of Texas at Austin before joining the Korgel Group for his PhD work.
Brian W Goodfellow is a PhD student working under Professor Korgel in the Department of Chemical Engineering at the University of Texas at Austin. His primary research areas include the development of copper indium gallium selenide (CIGS) nanocrystal-based photovoltaics, self-assembly of nanocrystals into complex superstructures and small-angle X-ray scattering of nanomaterials. He received his BSc in materials science and engineering from Cornell University in 2006.
Matthew G Panthani is a graduate student in the Chemical Engineering Department at the University of Texas at Austin. His research interests include the synthesis of semi-conductor nanomaterials, their electronic properties, their incorporation into devices and in situ transmission electron microscopy studies of nanomaterials. He received his BSc in chemical engineering from Case Western Reserve University in 2006.
Brian A Korgel is the Cockrell School of Engineering Temple Professor and the Matthew Van Winkle Regents Professor of Chemical Engineering at the University of Texas at Austin. His research group focuses on nanomaterials chemistry, developing new synthetic methods, understanding the fundamental properties of nanostructures and innovating technologies derived from the unique properties of nanomaterials.
Another approach to PV fabrication that has the processing attributes of organic materials but combines the proven device performance and stability of inorganic materials is to formulate nanocrystal inks that can be deposited under mild conditions using high-throughput continuous processes such as roll coating, spray-coating, spin coating, dip-coating, drop-casting, ink-jet printing, doctor-blading, screen printing, etc.10
If
solar cells could be made without the need for high-temperature or high-vacuum processing, these inks could dramatically lower solar cell module manufacturing costs. A lightweight solar cell on plastic would also significantly lower the installation costs. Since the module price accounts for only half of the total solar energy cost, this is a very important consideration.1
Conventional solar cell fabrication processes,
which require high temperatures, must be carried out on heavy glass or metal supports, which account for the majority of the weight in commercial solar modules. Light and flexible panels would change the way in which solar cells are installed, enabling more efficient transportation and installation. The ‘panels’ could be unrolled like a carpet and mounted on residential rooftops with no need for mounting brackets and structural reinforcement to the roof.
For
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Solar
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