The science behind innovation
There is no better place to start looking for innovation than at the scientific level with research that is not commercially vested in promoting any single product or technology. Argonne National Laboratory, Center for Nanoscale Materials (Argonne, IL) is one such centre. Argonne is a resource available to any company which wants to take advantage of leading edge technology.
Dr. Seth B. Darling, assistant scientist for Argonne says that there are a number of advances that look very promising in reducing the cost of solar cells, including novel desensitised solar cells using atomic layer deposition (ALD). “ALD allows three dimensional structures to be very thinly conformally coated. This reduces the distance that charges within the device have to travel”.
Another is advanced luminescence concentrators. Conventional solar concentrators are large devices that track the sun.
“This type of concentrator is stationary and it operates efficiently under diffuse light, which is what you need in low sun areas. We have developed a model to optimise parameters associated with this type of concentrator and we are using that to direct the development of some materials that are based on quantum dots. These are nanocrystals of inorganic semiconductor materials. It provides high luminescence efficiency and the nature of quantum dots allows tune-ability. You can tune their band gap, or tune the amount of energy they absorb. It also allows you to capture the very broad light spectrum, even into the near infrared part of the spectrum. There’s a lot of the energy that other solar technologies are not capturing,” he says.
“Argonne sits at the interface between the long-term research academia and industry. This is an important place to be. You need that unbiased bridge between the two worlds,” Darling says. “Ultimately of course, we are not a company, so our goal is to hand off our findings to a partner.”
Intermolecular, (San Jose, CA) is a different type of research resource. It focuses on combinatorial R&D i.e. performing multiple levels of similar research simultaneously.
“Our equipment looks like a semiconductor processing tool, but it is specifically built for high volume R&D. You can process many experiments very quickly in the same chamber in parallel as opposed to doing them one at a time using an entire solar substrate,” J. Craig Hunter, Vice President and GM solar and energy technologies, says.
Whether crystalline or thin-film, Hunter notes that even minor changes in processing will have an impact on the final solar product. Before making the investment to move into full production it is critical to understand exactly what your process windows are and exactly what the tolerances are for each of the individual process parameters.
“We offer a very IP secure way of doing that on a one-on-one basis with our customers,” Hunter says. “We can process a thousand unique solar cells per week, each with a different variation on critical things that affect the performance of that device. We also have software and metrology systems that quickly and fully characterise all solar cells and store it so the data can be accurately compared and analysed.”
Helping support innovation
Components, equipment and materials also fall into innovations that help solar PV manufacturers enhance both products and processes.
Components
BioSolar (Santa Clarita, CA) is on a mission to replace components used within solar photovoltaic (PV) modules with something 'greener'. This may sound like an oxymoron, but in truth, while solar is helping us move toward a renewable energy source, many solar PV component are not necessarily green. For example, the main material in backsheets is typically petroleum. BioSolar’s alternative is called the BioBacksheet.
“There are several different types of backsheets, but all are petroleum based. 90% of crystalline and certain amorphous silicon thin-film use one type. More modern thin-films, CIGS and Cadmium telluride also use a backsheet but they have more stringent requirements. They need an absolute moisture barrier,” David Lee, CEO says.
BioBacksheet uses a formulation based on cotton and a form of nylon resin made from castor bean oil. Lee says that it provides a perfect moisture barrier environment as well electric insulation.
The company is just gearing up to go into limited production. Samples will be available for all solar PV manufacturers to test by early 2010.
Equipment
Tyco Thermal Controls based in Menlo Park, CA came to the TFPV via semiconductors and then through flat screen TVs. “We had the big flat heaters that are needed to heat the flat screens and it was just a step to taking that up to the large-scale heating needed for thin-film vacuum deposition and for final thin-film lamination. One type of heater provides radiant heat for vacuum deposition and the other conductive heat for the lamination process.” Chris Mayes, Director of Product Marketing says.
“We make a very even heating substrate. Then we put a cable into the back. We allow for the edge effect where edges can get cooler and we put more cable into them. We’ve gone from a typical two foot by two foot to a six foot by six foot rough average. That, plus the change from the traditional heated oil media to the heated coil, makes the process more stable and requires much less maintenance,” Mayes says. “We see ourselves as an enabling technology,”
Materials
Heraeus Photovoltaic business unit was originally part of the Thick Film Division of WC Heraeus, the precious metals and technology group, headquartered in Hanau Germany. This past January it spun off into its own business unit and is growing fast with divisions in Germany, China, the USA and one soon to open in Taiwan.
The unit has developed a new front-side silver paste that offers higher efficiencies along with superior contact quality and aspect ratios on both mono and multi-crystalline wafers and a wide range of sheet resistance emitters.
“The chemistry of our latest SOL9235H cadmium-free silver metallization paste enhances the etching of the anti-reflective coating and significantly improves the contact quality of the cell,” Andy London, Heraeus PV business unit manager says.
According to London, it gives c-Si solar PV manufacturers efficiency values that are 0.3-0.5% higher than other products.
“We intend to produce two to three new products per year. If we can help people improve efficiencies and get better output, that is our goal,” London says.
Integral Technologies (IT), Inc. (Bellingham, WA) has a technology that is more on the brink currently; a pellet created from a proprietary blend of conductive polymers.
Development actually began when the company was contracted to come up with a flat panel antenna system for satellite tracking, which also needed a plastic bottom side that could carry an electric charge. No major company had such a material available.
“Conducting our own experiments, we came up with a mixture that worked,” Bill Robinson, CEO says. “We developed a pellet that could be injection moulded into a three dimensional shape or be extruded. It was also ideal for the bottom plate of a solar panel.”
Robinson says that the material is right for both c-Si an TFPV. In the thin-film area when two plates of glass are used, this can effectively replace the bottom plate. For crystalline silicon, he sees the material replacing the aluminium used to put solar panels together. “ElectriPlast has efficiencies similar to current materials, but is far less expensive,” he says.
The company currently has the capacity to manufacture up to 50,000 lbs of material a month. Robinson says that they will soon be targeting solar PV, and want to get involved and work with customers hands-on.
Another company working on a new technology that will be rolling out early next year is Plextronics Inc. (Pittsburgh, PA). Their offering to the solar PV world is also a conductive polymer technology but in the form of an ink.
Plexcore OC ink, is a multi-functional, customisable, conductive material compatible with a wide range of printing techniques. It creates an absorption layer of only about 200 nanometres. Plextronics refers to it as 3rd generation thin-film.
“Conductive polymers go into the terawatt capacity,” James Dietz, Vice President of Business Development says. “The technology is still in the development stage, but we make demos here. We buy substrates, glass or plastic, then we print our active or photovoltaic layer onto this and finish it to a completed module. It’s quite simple and that is the appeal.”
“We have over 20 customers now for our ink and it is a diverse base. One is for indoor applications because the product shows a very high efficiency under fluorescent lighting. Another is for a solar panel manufacturer. We only launched the initial product late last year and we are already seeing a lot of potential.”
c-Si, TFPV and beyond
All innovation culminates in actual production. As manufacturers move steadily toward soalr cell improvement, they draw on both in-house and outside expertise.
Abound Solar (Loveland, CO) creates thin-film solar cells based on cadmium telluride (CdTe) technology. According to Dennis Csehi, Vice President of Engineering, this technology greatly streamlines manufacturing and holds down cost while delivering competitive solar cell power.
“It’s a very simple process. It is all done in a vacuum. The semiconductor layer is all done in one shot. From there we do our backend processing which is laser-scribing followed by module assembly. Unlike others in the thin-film market our assembly is not a lamination process. We have a proprietary process that we use for putting the backplate and the active plate together,” Csehi says.
The company is currently producing products and field testing solar arrays. They recently passed certification of their process.
“We recently announced two customers in Germany; Juwi and Wirsol. They have long term agreements to buy our products and use them in large scale installations,” Csehi says.
Michael Bartholomeusz, CEO of Applied Quantum Technology (AQT), headquartered in Santa Clara, CA says that AQT’s mission is to achieve the highest cost/performance ratio of any solar cell manufacturer. “Our patented, proprietary technology is based on the production of CIGS-type thin-film photovoltaic cells using the reactive sputtering process. Sputtering is the proven standard for producing other high volume cost sensitive products such as hard and optical discs. This approach includes single-step deposition, nano-engineering, device-enhancing source materials, and simplified cell interconnect design,” Bartholomeusz says.
AQT intends to focus on cost reduction and performance enhancement via nano-engineering. The company is embarking on pilot production (15 MW) and has a customer, LOI (for a 2 MW installation) in place.
Another TFPV player that is getting ready to roll out in volume is Ascent Solar Technologies Inc. Look for this to happen in January, 2010 from the company’s new 30 MW headquarters in Thornton, CO.
Ascent Solar uses CIGS thin-film technology but on a clear plastic substrate. Also, its cells are both extremely lightweight and flexible. The manufacturing process is done at the module level using roll-to-roll, monolithic integration. The only way to produce a product at a module level is through monolithic integration, and monolithic integration needs to use a transparent insulator. Light has to go through it.
The process uses thermal co-evaporation to deposit the four metals; copper, indium, gallium and selenium onto the moving polyvinyl, plastic substrate. This forms the ideal CIGS compound in the ideal thickness.
“Producing at the modular level means we don’t have any external wiring. Everything is done internally just as in integrated circuit (IC) processing. That enables us to go to large modules and high voltage which is a big advantage,” Farhad Moghadam, President and CEO says.
The flex-cells produced by this technology can cut to order, from a module five meters long to the size of a credit card. The uniqueness of the product is that it remains flexible; not just the solar PV module but even after encapsulation. The modules achieve 11%+ efficiency.
“Our business model is focused on the BIPV, (Building Integrated PV) and EIPV (Electronic Integrated PV), not the utility market,” Moghadam says. “Our flex cells need no special framing or mounting. They can slip right into fabricated pockets and can be glued directly to metal or fabric surfaces.”
When talking about thin-film, Odersun is always on the leading edge of innovation. The most unique aspect of the Odersun solar cells is that they can be created in any size or dimension, as proven with the trapezoidal modules used to form concentric rings that powered the visitor centre buildings of the Olympic Park in Beijing in 2008.
Odersun has grown considerably since its pilot plant created the Beijing solution. It is now ramping up to full production, targeting both the BIPV and the custom consumer solar roofing markets.
“In Germany, many people have custom roofing designed. Because of this, roofing architects are seeking companies who can provide solar modules that can fit unique designs,” Dr. Hein Van der Zeeuw, CEO, says.
This flexibility of Odersun solar modules comes from the basic manufacturing methods. Cells are produced by creation of a Copper-Indium-disulphide semiconductor on long reels of Copper Tape (CISCuT). Being just 1 cm wide and 0.1 mm thick this copper tape is not only used to form the CIS semiconductor but also acts as the substrate and the carrier material for the solar cell. Using this patented “reel-to-reel” production process, the 0.001 mm thin active cell layer is created in only 3 stages.
Completed reels of solar cells are then cut into strips, slightly overlapped and interconnected using conductive glue to form SuperCells. The length of the individual solar cell strips determines the current that can be drawn, and the number of cells interconnected in series defines the voltage. The modules are composed of one or multiple SuperCells connected in parallel. They can be individually packaged in either a flexible film laminate or a rigid glass-film laminate. In this way the size, power and design of the modules can always be adjusted to suit each customer’s exact specifications.
In 2009 Odersun’s efforts went into building a 30 MW factory. Its next commercial project is for a railway station in Germany which will start construction in the first quarter of 2010. And there are three more 30 MW factories on the horizon for Odersun. These will be strategically placed globally for best market penetration.
Moving to crystalline (c-Si) technology, even with the relative maturity of this market, there is still a lot of ground-breaking going on. Much of it is in the area of developing better and leaner processes.
Applied Materials, Santa Clara, CA is at the forefront in this area. “As the world’s largest supplier of crystalline silicon (c-Si) production equipment, our systems are used in manufacturing the world’s most efficient commercially available solar cells,” Ken MacWilliams, Vice President of Technology and New Products for Applied’s crystalline silicon solar business, says.
One example is Applied Material’s project with Baccini Cell Systems (Baccini Esatto). Combining Baccini’s products and technologies with Applied’s expertise in processing technology, automation and R&D resources, results in world-class factory production tools for advanced c-Si solar cells.
The first of several applications of this collaboration is for double-printed metal line deposition. This has been shown to raise absolute cell efficiency by as much as 0.5%. “These systems’ high productivity, advanced ultra-thin wafer handling and extensive automation can drive significant cost reductions, resulting in lower cost per Watt,” MacWilliams says.
“Today, approximately 80% of PV solar panels produced are based on c-Si technology because it has shown excellent long-term reliability and performance over several decades of use. The cost of US$1/W will be demonstrated in a few years. Applied Materials will continuing to offer new and continuous improvement products (CIP) to fulfil current and next generation needs,” MacWilliams says.
Not all innovations are c-Si or TFPV. What about the best of both worlds? That’s how Sanyo (Tokyo, Japan) thinks. Its HIT (Heterojunction with Intrinsic Thin-layer) solar cell is an original technology. This hybrid combines a crystalline silicon substrate and amorphous silicon thin-film. To date, it offers the world’s best power generation level per unit of installation area, based on superior high energy conversion efficiency and temperature resistance.
“With crystalline silicon-type PV cells, the most important issue for reducing the cost of PV systems is the achievement of both energy conversion efficiency and a thin silicon wafer, which is the energy generation layer,” Robert Zerner, Business Development Executive, Solar Division says.
Sanyo’s most recent breakthrough HIT cell improvement was realised recently using a cell thickness of 98 micrometers, which is less than half previous solar cell thickness. This comes with a 22.8% cell energy conversion efficiency, which has been independently verified by the National Institute of Advanced Industrial Science and Technology.
While still confined to R&D and installation tests. Zerner says that this has a very promising future. “The key for Sanyo is achieving, We don’t do anything unless we can do it with 100% accuracy,” he adds.
Future Tech
Some innovations are well past the drawing board stage, but not quite ready to roll into full production. These are some that should be making the news within the coming year.
Shrink Nanotechnologies, Inc., Carlsbad, CA, produces a shrinkable plastic film. “One for this film is building PV solar cells, but not the type that are normally envisioned. Our technology involves solar concentrators,” Mark Baum, CEO says.
Ms. Sayantani Ghosh, PhD, assistant professor of Physics at UC Merced and consultant to Shrink Nanotechnologies explains that this technology is a completely unique process.
“In a solar cell you take sunlight, and convert it into electricity,” she says. “What we are doing is taking sunlight and converting it into light of a different colour. This different coloured light then falls onto existing silicon PV. The colour of the light is set to the PV’s preferred colour. It is like straining the sunlight into colours that will enhance the efficiency of the silicon.”
“Think about a window. Instead of glass, the surface of the pane would be a very thin solar concentrator between two layers of glass. The light of day will hit that solar concentrator. By using crystalline silicon around the edges of the pane, that silicon would absorb the photons coming off the quantum dots in the film. This would be absorbed into the system and ultimately be turned into electricity that could be used. This same technology can apply to home siding and roof shingles. It’s all about functionalising the surfaces of the buildings that people live and work in,” Baum says.
XsunX, Solar (Golden, CO), develops TFPV solar cell technologies and manufacturing processes. Intevac, Inc. provides magnetic media deposition equipment to the HDD industry. Put the two together in a joint business agreement and out comes a new level of equipment for manufacturing of CIGS thin-film solar cells.
“We came up with a way to integrate our thermal evaporation with their sputtering to create a new process that combined the best of both: high efficiency of thermal evaporation and the high throughput of sputtering,” Tom Djokovich, XsunX CEO says.
These systems take a 5” to 8” square thin-film and process it the same as it would a hard media disk. The HDD technology lays down the back contact and then the evaporation system deposits the CIGS layer. Then subsequent processes lead to the final application of the front contact layer. The systems are targeted to produce 600 to 1,000 cells per hour.
“Laboratories are working with small structures to test out CIGS PV cell samples; 4” x 4” or 6” x 6” to come up with new efficiencies. However, when scaling up to large format cells, it introduces variables. You have changed from what worked in the laboratory to something completely different. You look at CIGS and the contrast between what has been achieved in laboratories and what is seen in real production is almost 100% reduction in efficiency,” Djokovich says.
“The reality is that if you have something that technically works in a small structure, the goal should not be making it larger but to simply make it small but at a very high throughput – say 1000 per hour. That’s what we will do,” he adds.
Bringing it home
ABB is well known for automation and robots, but it also has a solar division that is dedicated to providing turnkey solar plants. While not a pure PV innovation, this is definitely where most of the innovations find a home.
“We produce everything that goes into that plant with the exception of the panels and the trackers,” Rick L Ulam, Business Development Manager says. “Even on the trackers though, we put in the automation and the motors,” he adds.
Based on the GPS location, ABB calculates the irradiance for that site and then designs and builds the optimum plant for the customer. It can do this because ABB is not tied to any one type of solar technology.
The unique integral automation system is able to turn inverters on earlier in the morning and shut them off later at night. Doing this over 20 years produces a lot more power. Even if a storm rolls in and panels are pulled in to a flat position the plant will still produce power. The automation system senses that and pulls in additional panels to compensate.
“We focus on the reliability of the plant from all aspects. Say an inverter goes down, it rearms automatically. Our automation system will sense what is going on in the plant and if it is not a fault condition will rearm itself. It is basically a ‘Smart Plant’,” Ulam says.
ABB currently has 9 projects in progress for concentrating solar power (CSP) and there are 6 for solar PV. “CSP is thermal power generation where a mirror trough works in the plant and focuses on a point. That heats up a working fluid. Then that working fluid goes through a heat exchanger and creates steam. That steam drives the turbines that generate the power. So we are involved in both CSP and straight PV,” Ulam explains. “ Right now the markets are dynamic and developers are hooking up with companies that can help them. That’s what we can do,” he adds.
Ending thoughts
Looking at the wide range of technologies that are either already in the field or that will be rolling out by mid 2010, it’s easy to see that nothing is yet a truly definitive leader.
It is an exciting time to be in the solar market and what we will be talking about by this time next year, may just be a gleam in the eye of an entrepreneurial solar PV engineer or scientist today.
About the author
Based in California, Joyce Laird has been writing for a wide range of industrial magazines for over a decade. Her extensive background in the semiconductor industry created a perfect transition to covering developments in photovoltaics.