Copper indium gallium diselenide (CIGS) is the favourite formulation in the CIS copper indium diselenide family of photovoltaic devices. It has very long life and some companies such as Nanosolar are printing it. Cadmium telluride thin film photovoltaics has gained market share from silicon because it is lower cost and easier to install - no heavy glass likely to shatter, no strengthening needed of the structure it is placed on. However, controlled disposal is usually required for cadmium containing compounds so the billions of dollars of orders now enjoyed by cadmium telluride photovoltaics suppliers are largely limited to large buildings and certainly not energy harvesting for small electrical and electronic devices. By contrast, CIS photovoltaics is on bags in Germany (See Odersun AG appoints new CFO) and planned for compact electric car recharging stations in Japan (See Quick charging system using solar panels and lithium ion batteries).
Although CIGS solar panels use less raw materials and are cheaper to manufacture than the more expensive crystalline silicon panels, manufacturing them on a commercial scale has proven more difficult. Researchers at the UCLA Henry Samueli School of Engineering and Applied Science are looking to change that with a new development that provides a low-cost solution processing method for CIGS-based solar cells.
Many new suppliers
Manufacturers all over the world are already gearing up for mass production, with companies like Solibro, Global Solar and Avancis already having produced their first solar cells in 2008. Centrotherm, a company that has been an active player in the arena of semiconductors, has redefined itself and is now a provider of CIGS turnkey solutions, a move that has led to a dramatic increase in its size (more than doubling its personnel since it entered the PV arena). Other interesting companies in the field include Solyndra and Nanosolar.
Solyndra produces CIGS solar cells for commercial rooftops but their solar cells are very different to the type of cells everyone is used to. The company employs cylindrical modules which capture sunlight across a 360-degree photovoltaic surface capable of converting direct, diffused and reflected sunlight into electricity. The panels are lightweight and allow wind to blow through them. The horizontal mounting and unique "air-flow" properties of Solyndra's solar panel design promise a substantially simplified installation process.
Solyndra claim to have an order catalogue of approximately $1 billion and that's one of the highly successful startups. Nanosolar on the other hand are trying their best to optimize their manufacturing process and achieve the high efficiencies that CIGS cells give in the lab on a mass production scale. That is unfortunately not as easy as it sounds and so, the company has had to face setbacks that have delayed their date of initiation of production repeatedly.
Similar issues were faced by Miasolé in California and Ascent Solar in Colorado, a company that has had substantial financial backing from the USAF. These companies are also trying to iron out the difficulties in their manufacturing processes and of course, the quicker that happens, the faster their product offerings will become available.
Low cost processing?
A team from the university may now have found a low-cost solution processing method with the potential for large-scale production for their CIGS solar cells.
Although efficiency levels of up to 20 percent have been achieved elsewhere, the processing method is expensive which makes manufacturing costs uncompetitive with current grid prices. With this new method, the scientists are able to reach the same efficiency levels whilst bringing the cost of manufacturing down significantly.
The copper-indium-diselenide thin-film solar cells developed by the team achieved 7.5 percent efficiency in the published study but have in a short amount of time already improved to 9.13 percent in the lab.
"We started this process 16 months ago from ground zero. We spent three to four months getting the material to reach 1 percent and today it's around 9 percent. That is about an average increase of 1 percent every two months," said Yang Yang, a professor in the school's Department of Materials Science and Engineering, and a member of the California NanoSystems Institute, where some of the work is being done.
Currently, most CIGS solar cells are produced using vacuum evaporation techniques called co-evaporation, which can be costly and time-consuming. The active elements - copper, indium, gallium and selenide - are heated and deposited onto a surface in a vacuum. Using vacuum processing to create CIGS films with uniform composition on a large scale has also been challenging.
The copper-indium-diselenide material created by Yang's team does not need to go through the vacuum evaporation process. Their material is simply dissolved into a liquid, applied and baked. To prepare the solution, they used hydrazine as the solvent to dissolve copper sulphide and indium selenide in order to form the constituents for the copper-indium-diselenide material. In solar cells, the "absorber layer" (either copper-indium-diselenide or CIGS) itself is the most critical to performance and the most difficult to control. Their copper-indium-diselenide layer, which is in solution form, can be easily painted or coated evenly onto a surface and baked. Advantages include a reduction in material waste and the potential for large-scale production of the solar cells using a roll-to-roll process - an important breakthrough in terms of cost.
They hope to reach an efficiency level of 15 to 20 percent, and full commercialization within the next 4 years. Ascent Solar Technologies, Inc a developer of state-of-the-art, flexible thin-film photovoltaic modules, announced that the company has manufactured a monolithically interconnected 5 meter long flexible light weight module on a polyimide substrate.
The lightweight design is expected to allow the module to be hand-carried if needed, as opposed to glass modules that have to be hoisted with a crane across rooftops. The module can produce 123 watts under standard test conditions with an aperture area efficiency of 9.1 percent. This length is a baseline for the company's development of large area flexible building integrated photovoltaic (BIPV) products with its strategic BIPV partners.
"This is the largest monolithically interconnected CIGS (copper indium gallium di-selenide) module on polyimide and may be the largest of any CIGS module regardless of construction," said Ascent's Prem Nath, senior vice president for product operations, in a news release. "The size and efficiency of this module make it a breakthrough for the emerging opportunities of flexible CIGS photovoltaic modules."
New advances at Ascent Solar
On 26th August 2009, Ascent Solar Technologies successfully tested its internal qualification of a packaging solution for its flexible monolithically integrated CIGS modules, suitable for energy harvesting on small devices. The packaging solution passed the standard, set out for the performance and long-term reliability thin solar modules, of 1,000 hours of damp heat testing.
Dr. Farhad Moghadam, CEO of Ascent Solar, commented that, "This is a breakthrough development not just for Ascent Solar but also for the advancement of flexible CIGS technology and the differentiating capabilities it brings to the market. We are very proud of this achievement which now sets the stage for certification of our products by external agencies. This is also well timed to meet the requirements of our initial production from the 30MW high volume manufacturing plant scheduled to commence at the beginning of 2010."
Earlier in 2009, Ascent Solar unveiled its new headquarters is to be located in Colorado USA. The new location will house the company's new 30MW capacity manufacturing lines that will produce solar modules that can power homes, commercial buildings and consumer devices. Ascent Solar has developed an integrated processing technique of CIGS production on high-temperature plastic substrate.
Ascent's Director of Investor Relations Brian Blackman said he knows of one other small European company working in this area that's still in the research and development phase. The CIGS based thin film material used in this module was manufactured using the company's unique 1.5 MW roll-to-roll manufacturing line. The module was encapsulated during the testing and qualification of equipment at the company's new 30 MW plant under construction in Thornton, Colo., Blackman said.
Production is expected to start at the more than $100 million facility at the beginning of 2010. The company's headquarters, also in Thornton, were purchased in 2008.
About Ascent Solar Technologies
Ascent Solar Technologies, Inc. is a developer of thin-film photovoltaic modules with substrate materials that can be more flexible and affordable than most traditional solar panels. These modules can be directly integrated into electronics, military and consumer portable power products, transportation systems, building elements, and space / near-space applications resulting in market differentiated solutions.
Top image: Odersun
For more attend: Energy Harvesting & Storage USA 2009