Why Thin-Film CIGS Solar Cells Are Poised for Big Growth

Investment in thin-film CIGS-(Copper, Indium, Gallium, and Selenium) based solar cell manufacturers has been very robust, with companies such as MiaSole, Global Solar, NanoSolar, Solyndra and others receiving significant funding to support their growth. This indicates confidence in thin-film CIGS technology.

Thin film is a process where material from a target source is coated onto a substrate via a plasma field. These thin films are minuscule — angstroms to microns thick — and therefore use a very small amount of material to achieve most coating thickness goals. Silicon solar cells use a wafer of Silicon (Si) — a 10 story building in thickness compared to thin films that are just microns thick.

The benefit to using a CIGS process is that it has the potential to dramatically reduce the cost of manufacturing with a high production yield. That means that when the CIGS thin-film process is perfected, the cost of CIGS solar cells will likely come down. [Nanosolar has announced their CIGS cells at an eye popping $.99 /Watt. They have thrown down the financial gauntlet to all other solar cell manufacturers.]

Solar cell production cost is dependent on the cost of the raw materials and the recent silicon shortage is driving material costs up for silicon-based solar cells. The shortage is compounded by the ever increasing demand for silicon in semiconductor industries. This shortage is providing additional incentive for investment in alternative thin-film solar cell technologies. In an attempt to determine some actual costs, I discovered that all solar thin-film companies view their costs as a closely guarded secret. They felt that revealing costs would give competitors an understanding of price elasticity (margin) and therefore they didn't want to talk about it.

Thin-film solar companies must balance target material quality and cost to find the most advantageous combination. Generally, higher quality target material costs more, sometimes significantly higher depending on the material. Material cost is very important because it determines the price of the solar cell and manufacturer's profitability. The lower the production cost, the lower the price. And the lower the price of solar cells the more businesses and home owners can afford to purchase.

Of the companies developing CIGS solar cells, three categorical approaches have emerged so far: using evaporation, nano particles, and thin film targets. How these manufacturers develop their processes in their respective categories will be the greatest area of technical differentiation and in large determine CIGS cell efficiency and cost.

To date, CIGS solar cell production has only made it from the lab to the production floor with evaporation. Each process strategy has limitations in part governed by the material form factor. For example, material for evaporation (the material is heated up until it vaporizes) is easy to obtain and use, however, the process itself can be inefficient in material usage, slow to coat substrates and difficult to control. Soft metals such as Gallium and Indium can be expensive (and difficult) to powderize into nano form, or at least into a usable form for thin-film particle placement in correct stoichiometry.

But there is a process that can lower costs much more quickly and thrust CIGS to the forefront of the PV market. Physical Vapor Deposition (PVD) or "sputtering" is fast, and perhaps ideal for CIGS cell production, however, usable target materials have proven elusive in the past. Targets are made up of material (in this case CuInGaSe or CuInGa) that is attached to a reusable backplate installed in a PVD system.

High density CIG targets are necessary because they have the potential to enable faster development and production of CIGS cell lines. Lower density material will have microscopic voids in the material that can be filled with contaminates such as oxygen or other things that may be present in the manufacturing process.

After years of research and development, I am happy to say that casted CIG targets are now available. Casted targets are most dense targets currently available. High density targets are important because they enable thin-film technicians greater control the plasma field that determines the thickness and consistency of the film.

Obviously, CIGS cell manufacturers need to purchase raw materials at the best possible price and the company that is able to use material the most effectively will have a cost advantage. When target materials are used, the actual utilization can range anywhere from 25% to 75% depending on the target type and system design and operation. This means that only a percentage of the total material on a target is used, the remainder must be machined off and reclaimed (melted down to be re-used).

In our three years of research and development in CIG target casting technology we have found that once casted targets are spent, roughly 95% to 98% of the material can be reclaimed (depending on the target condition). In addition, material loss in the casting process is generally less than 3%. Using casted CIG material should yield upwards of 90% total material utilization when you consider the ability to remove CIG from spent targets and cast it again.

What all this means is that when a CIGS cell manufacturer's investment in raw material should yield 90% real total usage of material in the chamber. In this way a company that invests $100,000 in raw material (Cu, In, Ga) for casting targets can get $90,000+ of that material directly in process. The only difference is an additional casting fee on spent material. In other terms, every 4^th to 5^th target can be made from reclaimed material. This model of casting services and target consumption should enable more attractive CIGS solar cell prices in the future.

If production costs are key to enabling lower solar cell prices and wider adoption of solar power, then I believe CIGS has an advantage and PVD using casted CIG targets is going to be a very large player in the manufacture of solar cells.

Greg Howard is the Vice President of Sputtering Materials, Inc., a material science company that specializes in PVD materials and is based in Reno, NV. Mr. Howard has over 13 years of experience in high tech industries and has published market research studies, white papers, and other research as an industry analyst. As VP, he now oversees company operations and research and development.