Role of the substrates in the ribbon orientation of Sb2Se3 films grown by Low-Temperature Pulsed Electron Deposition

Antimony selenide (Sb2Se3) is a p-type semiconductor, considered as an excellent photovoltaic absorber for its high absorption coefficient in the visible region and a nearly optimal band-gap for singlejunction solar cells. The simple binary composition, together with non-toxic and earth-abundant constituents make this material very promising toward industrial production of low-cost thin-film solar cells. Theoretical calculations and experimental data have confirmed that Sb2Se3 exhibits strong anisotropic optoelectronic properties, due to the presence of infinite covalent (Sb4Se6)(n) ribbons along the (001) direction, whereas weak van der Waals interactions occur between ribbons. In such anisotropic materials, electronic transport is strongly affected by crystal structure: when ribbons are aligned perpendicularly to the solar cell surface, a better collection of photogenerated current occurs, leading to larger photovoltaic conversion efficiencies. In order to understand the alignment mechanisms of ribbons, Sb2Se3 thin films were grown by LowTemperature Pulsed Electron Deposition (LT-PED) technique at different temperatures (from 200 degrees C to 400 degrees C) on a variety of substrates, such as glass, molybdenum, CdS, Fluorine-doped Tin Oxide (FTO) and nano structured ZnO. The structural and morphological characterization of the Sb2Se3 films, performed by out-of-plane and in-plane X-Ray Diffraction and micro-Raman spectroscopy, demonstrated that ribbon alignment along the surface normal is strongly dependent on the used substrate. The comparison between solar cells grown in substrate configuration on Mo and FTO, clearly demonstrates the influence of ribbon orientation on short-circuit current.