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impaginato corretto fullone_Layout 1 13/10/15 12.08 Pagina 37 Department of Engineering, ICT and Technologies for Energy and Transport Patent Title Title Method for producing thin-film multilayer solar Method for producing thin film multilayer solar cells. cells. Ref. CNR 10000 Ref. CNR 10000 Assignee(s): CNR CNR Institute: IMEM Main Inventor: Edmondo Gilioli Countries: IT Priority date: 21/11/2008 Abstract Abstract The present invention refers to a method for the fabrication of thin film multilayer solar cells by Pulsed The present invention refers to a method for the fabrication of thin film multilayer solar cells by Pulsed Electron Deposition (PED). This method allows to deposit in a single step the absorber layer of the cell, Electron Deposition (PED). This method allows to deposit in a single step the absorber layer of the cell, Cu(InGa)Se2 or CIGS, with the desired chemical composition, without needing further stages for cation Cu(InGa)Se2 or CIGS, with the desired chemical composition, without needing further stages for cation ratio adjustment or selenization treatments. Moreover all the layer of the cell (buffer layer, transparent ratio adjustment or selenization treatments. Moreover all the layer of the cell (buffer layer, transparent conducting oxide) can be grown by PED in the same vacuum system, by rotating a multi-target carrousel. conducting oxide) can be grown by PED in the same vacuum system, by rotating a multi target carrousel. Thanks to this technique, CIGS solar cells with a photovoltaic efficiency larger than 17% have been Thanks to this technique, CIGS solar cells with a photovoltaic efficiency larger than 17% have been fabricated. fabricated. Background Background Nowadays , CIGS-based solar cells represent a strong alternative to the silicon-based technology, since only Nowadays , CIGS based solar cells represent a strong alternative to the silicon based technology, since only 1/100 of the raw materials is needed to absorb the same solar light quantity as the Si cells ant to convert it 1/100 of the raw materials is needed to absorb the same solar light quantity as the Si cells ant to convert it into electrical current. Such a huge material saving mainly means reduced electricity costs: the electrical into electrical current. Such a huge material saving mainly means reduced electricity costs: the electrical power produced by thin-film solar cells already raised lower values than 0.50$/Wp, while the costs related power produced by thin film solar cells already raised lower values than 0.50$/Wp, while the costs related to the traditional Si-based technology hinders to decrease them under 0.70$/Wp. to the traditional Si based technology hinders to decrease them under 0.70$/Wp. Technology Technology PED technology is based on the interaction between a pulsed high-power e-beam and a bulk target of the PED technology is based on the interaction between a pulsed high power e beam and a bulk target of the material to be deposited as thin film (i.e. CIGS). The energy exchange between e-beam and target leads to material to be deposited as thin film (i.e. CIGS). The energy exchange between e beam and target leads to an immediate ablation of the latter, which evaporates as high-energy plasma and condensates on a an immediate ablation of the latter, which evaporates as high energy plasma and condensates on a substrate faced in front of it. This evaporation occurs out of thermodynamic equilibrium, thus preserving substrate faced in front of it. This evaporation occurs out of thermodynamic equilibrium, thus preserving the target stoichiometry on the thin film. the target stoichiometry on the thin film. Advantages and Applicatons Advantages and Applications While the traditional approaches to CIGS deposition (thermal co-evaporation or sputtering) are based on While the traditional approaches to CIGS deposition (thermal co evaporation or sputtering) are based on complicated and subsequent multi-step treatments, CIGS films are grown by PED in a single stage, thus complicated and subsequent multi step treatments, CIGS films are grown by PED in a single stage, thus enhancing the production rate of the solar cells. Moreover the possibility to fabricate the whole cell by PED enhancing the production rate of the solar cells. Moreover the possibility to fabricate the whole cell by PED can reduce the dead-time and the atmospheric contamination risks. can reduce the dead time and the atmospheric contamination risks. Development stage Development stage 17%-efficient solar cells with a CIGS absorber grown by PED have been recently obtained. This result is 17% efficient solar cells with a CIGS absorber grown by PED have been recently obtained. This result is very close to the world record efficiency achieved on CIGS cells by thermal co-evaporation (20%). Solar very closetothe worldrecord efficiencyachievedonCIGScells by thermalco evaporation (20%). Solar cells entirely fabricated by PED (absorber, buffer and transparent oxides) exhibit efficiencies larger than 37 cells entirely fabricated by PED (absorber, buffer and transparent oxides) exhibit efficiencies larger than 6%. 5%-efficient cells have been fabricated onto unusual substrates, as tile or plastic. 6%. 5% efficient cells have been fabricated onto unusual substrates, as tile or plastic.