Recycling of CIGS solar cell waste materials
Doctoral thesis, 2014
The increased interest in solar power over the last few decades has led to a constant development of existing and new types of solar cells. One type of solar cell that is making advances on the global market is copper indium gallium diselenide (CIGS) thin film solar cells. The advantage of thin film solar cells is that they require less semiconductor material than conventional silicon solar cells and as a result are more cost effective. However, the CIGS material contains the valuable and rare elements indium and gallium, which makes recycling of CIGS materials necessary in order to ensure a future supply and keep production costs down. In the future there will be a need to recycle all solar cells currently being installed, but at present the biggest issue is the large amounts of waste material that are generated from the solar cell production.
The use of recycled CIGS materials in new solar cells requires separation and purification (up to 99.999 %) of the elements. The goal of the work presented in this thesis was therefore to develop a recycling process for CIGS in which the elements are separated from each other, preferably with high enough purity to allow direct use in new solar cells without further purification.
In this work a new, innovative recycling process for CIGS material was developed. Firstly, the separation of selenium, as selenium dioxide, was achieved by oxidation of the CIGS material at elevated temperatures. The method resulted in a selenium recovery above 99 %. After reduction of the selenium dioxide the recovered selenium had a purity of 99.999 wt% with respect to scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and zinc, which are the elements that might decrease the solar cell efficiency.
Next the separation of the remaining elements was achieved with selective electrodeposition. Electrodeposition of copper and indium, using different potentials, resulted in an almost complete separation of the elements. High-temperature chlorination and solvent extraction was also tested for separation of copper, indium and gallium. However, electrochemical separation and was determined to be the promising separation method for future process development.