Cu(In,Ga)Se2 (CIGS) thin film solar cells

The development of photovoltaic (PV) absorbers proper for thin films based devices has become fundamental in the last decades to increase the efficiency to cost ratio of solar energy and, mainly, to save raw materials. In fact, the amount of material required for the realization of thin film solar cells is at least two order of magnitude lower than in the case of first generation PV devices. Among these second generation thin film devices, the alloy Cu(In,Ga)Se2 (CIGS) is one of the most promising material since its conversion efficiency on glass substrates reached 22.8% at laboratory level. A further cost reduction could be achieved developing new easily scalable procedures not only on rigid but also on flexible substrates, this feature being really attractive for building integrated and product integrated PV systems.
At MIB-SOLAR Center, an innovative hybrid sputtering-evaporation system for the deposition of CIGS thin film absorbers has been tested in collaboration with Voltasolar srl (www.voltasolar.it), a small Italian company. Such a technique employs the sputtering process to deposit the metal precursors on suitable rotating transfer cylinders, from which they are subsequently evaporated onto the substrate in Se atmosphere, with total deposition time lower than 15 min. The cylindrical geometry of the deposition chamber can be exploited for a continuous process (i.e. roll-to-roll deposition) and different substrates can be used (11x14 cm2 soda lime glass, 120x14 cm2 stainless steel or 120x14 cm2 polyimide substrates). This procedure allows to combine features of both sputtering and evaporation techniques, enabling a fine tuning of the stoichiometry and an easy transfer to industrial processes.

Research team: Profs. Maurizio Acciarri e Simona Binetti (Associate Professors), PhD Alessia Le Donne (Research Technologist)

Selected publications