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Rapporto RSE 17001376

Cu2MnSn4 and Cu2FeSnS4: new chalcogenide thin films for large-scale BIPV

Photovoltaic (PV) is the most promising renewable energy source that can meet the global energy demand while keeping low concentrations of CO2 in the atmosphere. To become a major energy source, improving the control of the energy demand, module costs should be reduced significantly and/or their energy conversion efficiencies should be increased. In particular, to reduce the module cost, thin film solar cells are a viable option due to their lower material usage, implementation on flexible substrates and inexpensive manufacturing potential. However, current materials for thin film (TF) solar cells (e.g CdTe and CIGS) suffer from concerns over resource scarcity (e.g. Te and In) and toxicity (e.g. Cd) respectively and are therefore limited to sub-terawatts deployment. To push up the market of TF solar cell on TW-scale, we are investigating the PV potential of two earth-abundant compounds belonging to the chalcogenides Cu2M(II)M(IV)S4 (with M(II) = Mn, Fe, Co, Ni, Cd, Hg; M(IV) = Si, Ge, Sn). We have focused our activity on Cu¬2MnSnS4 (CMTS) and Cu¬2FeSnS4 (CFTS) TF grown. For the first time, the deposition of these materials have been carried out via a vacuum two-step approach: a stack of metal precursors deposited by physical vapor depositions (PVD) on Mo-coated soda lime glasses was annealed in sulfur vapors. Two different PVD processes have been compared: thermal evaporation for CMTS and sputtering for CFTS. The control (reproducibility) and the effects of the most critical growth parameters have been further investigated and correlated with the TFs quality (homoge...

Photovoltaic (PV) is the most promising renewable energy source that can meet the global energy demand while producing low emissions of CO2 in the atmosphere. To become a major energy source, module costs should be reduced significantly and abundant materials should be employed. In particular, to reduce the module cost, thin film solar cells are a viable option due to their lower material usage, implementation on flexible substrates and inexpensive manufacturing implementation. These aspects are fundamental to assure the development of a large scale built-in PV production. However, current materials for thin film (TF) solar cells (e.g CdTe and CIGS) suffer from concerns over resource scarcity (e.g. Te and In) and toxicity (e.g. Cd) respectively, and are therefore limited to sub-terawatts deployment. To push up the market of TF solar cell on TW-scale, we started to study the PV properties of two earth-abundant compounds belonging to the chalcogenides family Cu2M(II)M(IV)S4 (with M(II) = Mn, Fe, Co, Ni, Cd, Hg; M(IV) = Si, Ge, Sn). We have focused our activity on Cu2MnSnS4 (CMTS) and Cu2FeSnS4 (CFTS) TFs. For the first time, the deposition of these materials have been carried out via a vacuum two-step approach: a stack of metal precursors deposited by physical vapor deposition(PVD) on Mo-coated soda lime glasses was annealed in sulfur vapors. Two different PVD processes have been compared: electron beam evaporation (EB-PVD) for CMTS and sputtering for CFTS.

The control (reproducibility) and the effects of the most critical growth parameters have been further investigated and correlated with the TFs quality (homogeneity, stoichiometry and possible secondary phases). The growth processes were optimized through the study of the structural, morphological and optical properties of the TFs. Prototypal CMTS solar cells has been finalized and post-process thermal treatments have been tested to increase our best efficiency value up to 0.83% (Voc: 354 mV, Isc: 5.8 mA/cm2, FF: 40%). At the moment, this value is the world record efficiency for the CMTS based PV devices.