When it comes to power, everybody thinks about money and how we should make power-generating devices like solar cells become more efficient (read: more stuff for the same money and size). Thin film solar cells are yet another competitor to classic ones, and attract customers through the fact that they’re thin, flexible and cheap. And they’re also pretty inefficient (20% at most).
CIGS thin-film solar cells are made of a thin layer of copper, indium, gallium, selenium, and sulphur. A 30 percent efficiency is now possible to be obtained through the work of several researchers from Mainz University in Germany, headed by professor Dr. Claudia Felser. The scientists used high performance computers to simulate the characteristics of CIGS cells. They even calculated an optimum indium:gallium recipe: 70:30.
Indium and gallium atoms have been discovered not to be distributed equally throughout the CIGS material. Just below normal room temperature (25 degrees Celsius), the material passes through a phase in which the indium and gallium are completely separate. If the material is heated to above this demixing temperature, differently sized clusters of indium and gallium atoms do form. The higher the temperature, the more homogeneous the material becomes. It has now become apparent that gallium-rich CIGS is always less homogeneous than indium-rich CIGS.
The optoelectronic properties of the gallium-rich material are poorer because of this lack of homogeneity, making the CIGS cells less efficient. A way to manufacture efficient cells would thus be to produce the material at higher temperatures, when it becomes more homogeneous. Then, after sufficiently mixing the materials at higher temperatures, the cell has to be cooled down quickly to maintain the homogeneity.
The glass substrate that is used for solar cells also has a big role in manufacturing at higher temperatures to ensure the homogeneity. Schott AG from Germany has manufactured a special type of glass allows temperatures to be increased over 600 °C. Being more homogeneous, the CIGS cells are thus more efficient and have high chances to beat conventional solar cells, approaching a theoretical 30%.
Even at lower efficiency, CIGS solar modules produce more kWh per day when compared to crystalline silicon technology in hot climates and low light conditions. The hotter it gets the poorer any solar module will perform and Stion CIGS solar modules offer one of the best temperature coefficient rating at -0.26% which is far lower than the -0.44% to -0,50% temperature coefficient typically found mono crystalline solar cells. CIGS solar’s ability to produce power earlier in the morning and later in the afternoon makes them an ideal substitute for expensive silicon based technology. And when you consider the 92.92% PTC to STC ratio that beats many of SunPower
®’s solar module models, Stion CIGS solar modules http://vimeo.com/82425642 makes perfect sense at their much lower price.