Low-dimensional antimony-chalcogenide materials have received an outstanding interest for photovoltaic (PV) devices in the last years. They show high stability, low environmental impact, low cost, low carbon footprint and high technological flexibility. Currently, efficiencies above 10% have already been achieved for Sb2(S,Se)3-based solar cells [1]. On the other hand, Sb-Ge chalcogenide material is well studied as phase change material for different applications, especially when using Te as chalcogen [2]. However, up to our knowledge, the combinations of Sb-Ge chalcogenide semiconductors have not been integrated in solar cell devices. In this work, Sb-(Ge)-Se thin films are grown by selenization of co-evaporated Sb-(Ge) films on Mo/SLG and SLG substrates. The properties of Sb-Ge-Se layers are compared with those of Sb2Se3 thin films. The effect of the selenization process on the structural, morphological, compositional and optical properties of the Sb-(Ge)-Se compounds is investigated. Different growth parameters, such as the maximum selenization temperature and Se added during the thermal treatment, have been investigated in these devices. Independently from the used growth parameters, all Sb2Se3 absorbers show an orthorhombic structure with [hk1] preferred orientation, and a compact structure free of pinholes, while the Sb-Ge-Se active layers show the co-existence of Sb2Se3 and GeSe2 phases. The co-existence of these two phases is corroborated by Fourier-transform infrared spectroscopy (FTIR). Sb-Ge-Se thin films´ band gap energy Eg varies from 1.4 to 1.8 eV depending on the Ge content, as determined by ellipsometry spectroscopy. First efficient Sb-Ge-Se thin-film solar cells have been fabricated using these new absorbers and device efficiencies of 5.4 % and 1.3 % are achieved for Sb2Se3 and Sb26Ge6Se68-based films respectively. C-V and DLCP measurements performed in both type of solar cells, indicate a high defects concentration when introducing Ge in the absorber layer, in agreement with the device performance. This is an indication that the (GeSe2)x(Sb2Se3)1-x system is more defective than the Sb2Se3 material. TEM investigation of Sb-Ge-Se and Sb2Se3 solar cells reveal a different CdS/Sb-(Ge)-Se heterojunction that can explain the limitation of the PV devices when Ge is incorporated in the structure.
More investigations are carried out to understand performance limitation in the solar cells based on these new thin-film absorbers. Finally, we will discuss the possible
improvements of the current devices and the potential of these promising and sustainable chalcogenide material for outdoor/indoor/thin film PV applications