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: Prof. Simona Binetti (Full Professor) and prof. Maurizio Acciarri (Associate Professor)

Selected publications

• Acciarri, M., Le Donne, A., Marchionna, S., Meschia, M., Parravicini, J., Gasparotto, A., Binetti, S. “CIGS thin films grown by hybrid sputtering-evaporation method: Properties and PV performance” Solar Energy 175, 16 (2018)
• Parravicini, J., Acciarri, M., Murabito, M., Le Donne, A., Gasparotto, A., Binetti, S. “In-depth photoluminescence spectra of pure CIGS thin films” Applied Optics, 57 (8), 1849 (2018)
• A. Le Donne, D. Cavalcoli, R.A. Mereu, M. Perani, L. Pagani, M. Acciarri and S. Binetti,“Study of the physical properties of ZnS thin films deposited by RF sputtering” Materials Science in Semiconductor Processing 71, 7-11 2017
• J. Parravicini, M. Acciarri, A. Lomuscio, M. Murabito, A. Le Donne, A. Gasparotto, S. Binetti ,“Gallium In-Depth Profile in Bromine-Etched Copper–Indium–Galium–(Di)selenide (CIGS) Thin Films inspected Using Raman Spectroscopy” Applied Spectroscopy 71(6), 1334-1339 2017
• S.Binetti, P. Garattini, R. Mereu, A. Le Donne, S. Marchionna, A. Gasparotto, M. Meschia, I. Pinus, M. Acciarri, “Fabricating Cu(In,Ga)Se2 solar cells on flexible substrates by a new roll-to-roll deposition system suitable for industrial applications ” Semicond. Sci . Technol. 30, 105006 2015
• R.A. Mereu, A. Le Donne, S. Trabattoni, M. Acciarri, S. Binetti “Comparative study on structural, morphological and optical properties of Zn2SnO4 thin films prepared by r.f. sputtering using Zn and Sn metal targets and ZnO–SnO2 ceramic target" Journal of Alloys and Compounds 626, 112-117 2015
• R.A. Mereu, S. Marchionna, A. Le Donne, L. Ciontea, S. Binetti, M. Acciarri “Optical and electrical studies of transparent conductive AZO and ITO sputtered thin films for CIGS photovoltaics" Phys. Status Solidi C 11(9), 1464–1467 2014
• R.A. Mereu, S. Marchionna, A. Le Donne, L. Ciontea, S. Binetti, M. Acciarri “ZnO:Al/i-ZnO bi-layers deposited on large substrates by pulsed D.C. magnetron sputtering for chalcogenide photovoltaics" Ceramics International 40, 14595–14599 2014
• M. Acciarri, A. Le Donne, M. Morgano, L. Caccamo, L. Miglio, S. Marchionna, R. Moneta, M. Meschia and S. Binetti Hybrid sputtering/evaporation deposition of Cu(In,Ga)Se2 thin film solar cells Energy Procedia, Volume 10, 138-14 2011
• M. Acciarri, S. Binetti, A. Le Donne, B. Lorenzi, L. Caccamo, L. Miglio, R. Moneta S. Marchionna and M. Meschia Development of a hybrid sputtering/evaporation process for Cu(In,Ga)Se2 thin film solar cells Cryst. Res. Technol. 46, No. 8, 871 – 876 2011