Third generation thin film solar photovoltaic technologies on track to breakthrough

Third-generation thin-film photovoltaic (PV) solar devices are beginning to emerge in the marketplace after approximately 20 years of research and development, due to the insight of leading material developers such as Konarka and Plextronics in the organic photovoltaics (OPV) domain, and Dyesol, EPFL, G24i, Mitsubishi and Peccell on the dye-sensitized cells (DSC) front. Both DSC and OPV technologies lag far behind on the efficiency curve when compared to conventional solar (i.e., >20 percent efficiency), so they will likely succeed in markets where their low cost, substrate flexibility, and ability to perform in dim or variable lighting conditions provide them with a significant competitive advantage. DSC will target larger area BIPV applications while OPV will find its application in lower power consumer applications. These are some key findings of Greentech Media's recently published study "Third generation thin film solar photovoltaic technologies". The solar report in November 2009 in cooperation with GTM Research highlights the development and status quo of OPV and DSC and gives an outlook on market potentials.

Solar cell manufacturing with roll-to-roll methods. Courtesy: GTM Research
Solar cell manufacturing with roll-to-roll methods. Courtesy: GTM Research

The success of penetrating existing and new PV markets however will depend on many variables, including costs in $/Wp, as well as $/m2 of product and power availability (kWh/Wp/annum); the technical and environmental profile of each newly introduced technology; and added value for the consumer and architects as well as the ease of production and the scale at which a production plant becomes economically feasible. At this stage, third-generation PV is not at a price point to be able to compete directly with silicon-based cells or the more exotic thin-film technologies, but it will nevertheless play a significant energy role in applications and markets that conventional solar materials will never be able to penetrate. These include low-power consumer electronics, outdoor recreational applications, and BIPV applications.

Consumer Electronics: Solar charging for mobile devices

G24i’s low-cost solar charger: DSCs provides affordable power to recharge mobile phone batteries and other mobile electronics in the rural areas of Africa. Courtesy: G24.
G24i’s low-cost solar charger: DSCs provides affordable power to recharge mobile phone batteries and other mobile electronics in the rural areas of Africa. Courtesy: G24.

There is considerable anticipation over the pending production of these novel devices, since they will be able to come in at price points far below existing technologies, though initially they will likely not be as reliable. One of the first commercial DSC products offered last year was G24i’s low-cost solar charger, which provides affordable power to recharge mobile phone batteries and other mobile electronics in the rural areas of Africa. This is a vast market, where some 160 million mobile phones were sold in 2008 (comprising 20 percent of world sales last year), and phenomenal growth of up to two billion handsets is forecast by 2015.

LG Electronics, Samsung, and Sharp recently demonstrated mobile phones powered by silicon solar panels, and it seems only a matter of time until DSCs will replace these panels. In fact, GTM Research believes that all mobile devices should have some sort of solar-power feature to “trickle-charge” batteries when they are not in use, a feature that will increase the duration between full charges. The objective is to arrive at a technology that is small, but at the same time is able to convert energy efficiently. DSCs will likely be the prime candidate that will achieve both of these ends in the future.

Third-generation thin-film-based technologies offer a significant advantage over conventional silicon and over other standard thin-film technologies, in that they do not lose power dramatically under shaded or variable light conditions, but rather continue to collect energy even in low-light situations, making them an excellent source for lighting applications. Several developers are working to take advantage of DSCs’ ability to power various non-grid-based lighting applications. Sony has demonstrated elegant Japanese-style lanterns, as a proof of concept design for using DSCs as power source. A variety of low-power consumer applications are beginning to emerge on the market.

 

Solar for outdoor recreational applications: Increasingly efficient levels of performance and associated lower costs

Picture: Konarka's mobile solar charger, supplied by Power Plastic. Courtesy: Konarka Technologies, Inc.
Picture: Konarka's mobile solar charger, supplied by Power Plastic. Courtesy: Konarka Technologies, Inc.

Conventional solar panels have been used in a variety of outdoor recreational settings for some time, especially in cars, but also in boats. Given the world market’s increasing demand for “green” energy, this market offers a significant opportunity, but will require more efficient and cost effective materials.

The principal problems with such energy systems arise from the relatively small amounts of energy being generated, often at disproportionately high costs. The advent of third-generation thin-film solar technologies is set to change this, given the increasingly efficient levels of performance that are now being obtained, especially with DSC and OPV devices and their associated lower costs.

 

BIPV

With the renewed interest in solar energy that is developing across the board, BIPV technology has progressed to third-generation systems, whereby solar modules are being fully integrated into the building envelope and are therefore able to replace conventional building materials. It is this generation from which the largest opportunities will likely emerge, because these products can be applied to a variety of settings including roofs (roof-integrated photovoltaics or RIPV), walls, facades, and windows. Corus is developing products for use in RIPV applications using Dyesol’s DSC materials, and will be one of the first companies to commercialize its metal-based RIPV products, with early models appearing by 2011.

Corus believes that many industrial buildings, which are typically covered with steel sheets, will be generating solar electricity using its solar paint, especially given that there are in excess of one billion square meters of coated steel roofs erected each year around the world. Solar windows and skylights present an exciting market opportunity given the huge window areas available to collect solar energy and the aesthetically appealing nature of these products. The transparency of these windows does change, which may be beneficial to workers’ or residential dwellers’ comfort, and could reduce glare and heat at the sunniest times of the day.

 

Left: Dye solar cells by Dyesol. Right: Power Plastic by Konarka. Courtesy: Dyesol Limited; Konarka Technologies, Inc.
Left: Dye solar cells by Dyesol. Right: Power Plastic by Konarka. Courtesy: Dyesol Limited; Konarka Technologies, Inc.

Konarka Technologies is collaborating with Arch Aluminum & Glass to develop solar materials to replace conventional building materials for integration into semi-transparent glass for various commercial BIPV applications. These materials are more flexible, lightweight and transparent, making them more aesthetically suitable for BIPV applications.

Other active developers include Fraunhofer ISE/ColorSol Consortium, New Energy Technologies, and Solarmer. Konarka’s PowerPlastic for rooftop applications is expected to be competitive in terms of both cost and efficiency by 2010. Another of Konarka’s partners in BIPV is SKYShades, which itself views the installation of integrated ‘solar OPV membranes’ over existing sheet metal roofing systems as a substantial growth opportunity. ‘Roofs’ have historically been non-income earners for property owners, and now they are able to offer an installation which can generate ‘clean, green’ power to augment electricity needs – and in the case of larger roof areas – to feed into the grid. In either case, there will be a cost savings redirected to the property owner. The company has been working with Konarka for the past few years and is currently demonstrating its novel structures at a factory in Brisbane, Australia, where it has installed a 200m2 solar membrane structure on the rooftop. It plans for wide-scale commercialization by the end of 2009 or early 2010.

 

Power Generation

Flexible OPV cell manufactured by Fraunhofer ISE , (Germany). Courtesy: Fraunhofer-Institut für solare Energiesysteme (ISE)
Flexible OPV cell manufactured by Fraunhofer ISE , (Germany). Courtesy: Fraunhofer-Institut für solare Energiesysteme (ISE)

Harvesting energy directly from sunlight using DSC and OPV technologies is a way to address global energy needs, while at the same time minimizing detrimental effects on the environment by reducing atmospheric emissions, especially CO2. DSC and OPV devices are easier to manufacture than current silicon-based PV technology, and if efficiency and costs can be improved, then they show great potential as a source for both on-grid power generation, as well as off-grid systems.

NREL has stated that DSC technology has the potential to produce electricity that is “grid competitive,” meaning, at the same cost to the consumer as electricity supplied from fossil fuel power stations.

On a practical level, researchers at Risø’s DTU have been working with Mekoprint A/S and Gaia Solar A/S, and connected their OPV solar cells to the grid at Risø, at a cost of €15/W in March 2009 and less than €5/W by the end of 2009.

About 1.6 million people live without electricity in the world, so there is a real need to provide electricity for off-grid applications, especially in Africa and India. The “Lighting Africa” program is addressing the need to develop cheap and efficient lighting and energy solutions for those live without access to the electricity grid. As part of this program, G24i and Lemnis are developing off-grid lighting devices that use light emitting diodes (LEDs) and DSCs.

 

Evolution of third-generation thin-film solar materials and technologies

Foto: SKYShades
Foto: SKYShades

One of the greatest appeals of third-generation thin-film solar cells is that they can be manufactured using solution-based, low-temperature roll-to-roll manufacturing methods, incorporating conventional printing techniques on flexible substrates, which presents the opportunity for a more economical alternative for solar cells within the next few years. Such new low-cost third-generation solar cells will offer larger surface areas with enhanced performance (see Table I-1 at the end of this report).

Joe McKenna SKYShades Executive Vice President on left and Barry Maranta President SKYShades (4th from left) explain to Lake Highlands College Principal, Staff and selected students how the Power Plastic is applied to SKYShades umbrellas.

However, to enable long-term use of DSC and OPV in conventional electricity generation, e.g., in grid-connected or stand-alone rooftop applications, significant progress in cell efficiency, stability, and lifetime are needed. With respect to lifetime, there is much discussion going on as to whether the technologies need to have the same lifetime as silicon-based PV (20+ years) for economical rooftop use, or whether shorter lifetimes of around 5 years, especially for very low-cost modules, could be deemed acceptable (this is, in fact, the direction that Konarka and SKYShades are taking). However, there is some evidence to suggest that for mass production for top grid-connected and building-integrated solar cells, optimal lifetime duration should be at least 20 years, since investors are less likely to support a technology with low efficiency and lifetime.

 

DSC

Picture: BIPV panel by Dyesol. Courtesy: Dyesol Ltd.
Picture: BIPV panel by Dyesol. Courtesy: Dyesol Ltd.

Early DSC prototypes were laminated between two sheets of glass, but more recently, flexible materials are being used to give higher cell efficiencies and lifetimes. Professor Michael Gratzel at EPFL in Switzerland first demonstrated the technology in 1991. Just 16 years later, in 2007, there was a major investment in the first DSC manufacturing plant with annual production capacity of 20 MW in the U.K. by G24i (using technology licensed by Konarka Technologies), with an additional 25 MW capacity to become operational by the end of 2009. G24i plans for mass production into several markets by 2011, including consumer electronics and BIPV.

The best device efficiencies for the solid-state DSCs currently rate at approximately 8 percent; otherwise, DSCs exhibit the highest efficiencies of any third-generation thin-film solar technology; laboratory cell and tandem cell efficiencies of up to 12 percent have been reported. Some important drivers of innovation in the realm of DSC technology are summarized in Table I-2. at the end of the report (DSC TECHNOLOGY CHAMPIONS)

In order to enhance the performance and lifetime of DSCs, several advances in material development are being sought. Commonly used dye sensitizers in commercial cells are fabricated from costly inorganic ruthenium-based dyes (from Dyesol and Solaronix), including N-3 and N-719 dyes. Copper-based dyes, however, may become the next generation of inorganic dyes, given their lower cost and increasingly efficient performance. By combining different colored dyes in a tandem DSC design, the range of light absorption has been extended and is yet another way to enhance cell efficiency and stability, as demonstrated by projects undertaken by Panasonic Works, Sony, Kyushu Institute of Technology, and KIST.

Preliminary results reveal an overall increase in efficiency by up to 50 percent and stabilities up to 85°C for 12 years, levels that could even allow for usage in BIPV applications. It seems likely that organic dyes, such as those based on carbazoles, indolenes, and porphyrins, will become increasingly important, as they are widely available and are less expensive than are their inorganic counterparts. Until recently, the electrolyte system used in DSCs was based on organic liquid solvents, but since these are heat-sensitive and prone to leakage, other more stable alternatives are being investigated.

 

OPV

Picture: Computerised tomography of a polymer metal oxide solar cell. Courtesy: Universität Ulm
Picture: Computerised tomography of a polymer metal oxide solar cell. Courtesy: Universität Ulm

Research into OPV was initiated in the 1950s, but it was not until 1986 that Ching Tang’s research team at Kodak achieved a breakthrough discovery, finding that by combining donor and acceptor materials in one solar cell, cell efficiencies could be increased significantly, up to one percent. From 1986 to 2007, pioneering researchers in the field included Serdar Sariciftci (Johannes Kepler University), Alan Heeger (UCSanta Barbara), Kwanghee Lee (GIST, South Korea) and David Carroll (Wake Forest University).

Recent research result giving new insights on the function of polymer solar cells that can be produced rapidly and simple – even in a roll-to-roll process.

Taken together, these researchers' efforts’ are primarily responsible for enhancing the performance of the model P3HT: PCBM bulk heterojunction device to five percent efficiency and stability of one year. Materials development is now being focused on novel polymers and small molecules, as well as electrode and encapsulation materials. The establishment of viable supply chains to provide these materials with the required purity is essential. A vital factor restricting the efficiency of OPV devices is their inability to absorb a large enough fraction of the solar spectrum, since the commonly used organic materials are limited to the visible part of the spectrum, whereas much of the sun energy is in the neighboring infrared region. Typical materials employed in OPVs absorb relatively little of the incoming light, resulting in poor efficiencies. As such, researchers are working to overcome this limitation by developing high efficiency OPV cells that are developed by stacking and connecting individual cells in series, as well as using lower-band gap materials with absorption in the infrared, thereby optimizing the absorption of incident light. This has been well illustrated by the on-going work of researchers at UCSB, GIST, and the University of Laval (which is one development partner of Konarka).

 

DSC Suppliers and OPV Suppliers

Product variations of Konarkas "Power Plastic". Courtesy: Konarka Technologies, Inc.
Product variations of Konarkas "Power Plastic". Courtesy: Konarka Technologies, Inc.

Despite the fact that DSC technology was discovered several years after OPV technology, it is the first to offer commercial products, due to the development efforts of EPFL and a host of R&D organizations, in addition to global economic and environmental drivers. Dyesol and Solaronix are the main material developers supplying G24i (battery chargers for Africa in 2009) and Corus (metal solar roof panels in 2011). Other developers likely to follow in the next few years include 3G Solar, Fraunhofer ISE/ColorSol, Fujikura, and Pecell Technologies. In addition, there are many DSC developments going on at the corporate and SME levels in Japan, but to date, there has been little publicity covering these developments.

As NREL’s roadmap for OPV points out, the main challenges holding back the large-scale commercialization of this technology are low cell efficiency (which needs to be improved to achieve a rate of least 10 percent), and short lifetime (which must be extended to at least three years). Along with these improvements should come lower cost electricity generation, with a target rate of $1 per watt considered a viable reality for 2010.

OPV cells are expected to become commercially available in 2010 from principal developers and suppliers including Heliatek, Konarka Technologies, Mitsubishi, Plextronics, and Solarmer Energy.

 

The Author:

Philip Drachman is a Research Analyst at GTM Research. He has authored research reports on topics including thin-film photovoltaics, printed photovoltaics, building integrated photovoltaics and printed electronics since 2006. Drachman began his career as a Research Scientist working for Exxon Chemical in 1988, and subsequently gained valuable experience and insights in technical and marketing roles in the energy and associated industries. His academic background is as a materials scientist and he holds a Master of Science degree in Organometallic Chemistry from Queen’s University, Canada.

Further information and purchasing: http://www.gtmresearch.com/report/third-generation-thin-film-solar-technologies

1. Comparison of third generation thin film solar photovoltaic technologies

Quelle: GTM Research
Quelle: GTM Research

2. DSC TECHNOLOGY CHAMPIONS

Quelle: GTM Research
Quelle: GTM Research

3. OPV TECHNOLOGY CHAMPIONS

Quelle: GTM Research
Quelle: GTM Research