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impaginato corretto fullone_Layout 1 13/10/15 12.08 Pagina 39 Department of Engineering, ICT and Technologies for Energy and Transport Patent Title Title Method for fabricating thin-film solar cells. Method for fabricating thin film solar cells. Ref. CNR 10335 Ref. CNR 10335 Assignee(s): CNR CNR Institute: IMEM Main Inventor: Stefano Rampino Countries: IT Priority date: 26/05/2014 Abstract Abstract The invention allows to grow thin film solar cells by means of Pulsed Electron Deposition process (PED). The invention allows to grow thin film solar cells by means of Pulsed Electron Deposition process (PED). This technique permits the realization of solar cells with a net reduction of the costs thanks to lower This technique permits the realization of solar cells with a net reduction of the costs thanks to lower temperatures and excellent stoichiometric transfer of the material from the target to the substrate. temperatures and excellent stoichiometric transfer of the material from the target to the substrate. These ideas are suitable for this process and provide a solution of two critical issues: the uniformity of These ideas are suitable for this process and provide a solution of two critical issues: the uniformity of the deposition over large areas and the increase of the PED stability of the process over time. The first the deposition over large areas and the increase of the PED stability of the process over time. The first one is resolved through the optimization of an array of PED sources arranged below a substrate moved one is resolved through the optimization of an array of PED sources arranged below a substrate moved convenientely. The second one can be overtaken by directly heating the substrate via the Joule effect convenientely. The second one can be overtaken by directly heating the substrate via the Joule effect (limiting dispersions and massive elements that usually reaches very high temperatures in the chamber (limiting dispersions and massive elements that usually reaches very high temperatures in the chamber heating all the walls and the device located inside). heating all the walls and the device located inside). Background Background The CuInGaSe (CIGS) is reaching a great interest as material for photovoltaic application. Thanks to its high The CuInGaSe (CIGS) is reaching a great interest as material for photovoltaic application. Thanks to its high 2 2 optical absorption coefficient, CIGS can absorb the totality of the solar light in a few microns thickness optical absorption coefficient, CIGS can absorb the totality of the solar light in a few microns thickness allowing to realize photovoltaic cells with efficiency values above 20%. However, the techniques used so far allowing to realize photovoltaic cells with efficiency values above 20%. However, the techniques used so far (co-evaporation and sputtering) require high substrate temperatures (500-600°C) and cause high waste of (co evaporation and sputtering) require high substrate temperatures (500 600°C) and cause high waste of material on the walls of the deposition chamber. material on the walls of the deposition chamber. Technology Technology Thanks to the typical features of the PED technique, the growth of the CIGS layer occurs preserving Thanks to the typical features of the PED technique, the growth of the CIGS layer occurs preserving completely the stoichiometry of the target material even at low temperatures (300°C). However, the completely the stoichiometry of the target material even at low temperatures (300°C). However, the temperatures involved lead to a degradation of the performance of the source if maintained for long time temperatures involved lead to a degradation of the performance of the source if maintained for long time and the deposition from a single gun does not guarantee a high yield for the industrial production. and the deposition from a single gun does not guarantee a high yield for the industrial production. Advantages and Applicatons Advantages and Applications The ideas developed in this patent arise from the need to insert the technique PED inside a continuous The ideas developed in this patent arise from the need to insert the technique PED inside a continuous production line of photovoltaic modules and allow both to maintain performance of the other sources for production line of photovoltaic modules and allow both to maintain performance of the other sources for long periods thanks to the heating of the substrate only through Joule effect both grow mini-modules long periods thanks to the heating of the substrate only through Joule effect both grow mini modules 2 2 16x16cm thanks to a suitable arrangement of an array of sources PED. 16x16cm thanks to a suitable arrangement of an array of sources PED. Development stage Development stage Several solar cells have been grown by PED with efficiency higher than 15% using a metal-coated soda-lime Several solar cells have been grown by PED with efficiency higher than 15% using a metal coated soda lime glass substrate heated by joule effect. It is still in the completion phase a vacuum chamber for the glass substrate heated by joule effect. It is still in the completion phase a vacuum chamber for the development of a pre-industrial production system for CIGS solar cell based on the PED technique where development of a pre industrial production system for CIGS solar cell based on the PED technique where the sources have been positioned taking in account the results obtained thanks to the simulations 39 the sources have been positioned taking in account the results obtained thanks to the simulations presented in these studies. presented in these studies.