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

Antimony selenide (Sb 2 Se 3) 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 single-junction 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 Sb 2 Se 3 exhibits strong anisotropic optoelectronic properties, due to the presence of infinite covalent (Sb 4 Se 6) 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, Sb 2 Se 3 thin films were grown by Low-Temperature Pulsed Electron Deposition (LT-PED) technique at different temperatures (from 200 °C to 400 °C) on a variety of substrates, such as glass, molybdenum, CdS, Fluorine-doped Tin Oxide (FTO) and nanostructured ZnO. The structural and morphological characterization of the Sb 2 Se 3 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. Image 1 • Pulsed Electron Deposition allows fast deposition of stoichiometric Sb 2 Se 3. • No high temperature annealing nor selenization in toxic gas are needed for Sb 2 Se 3. • Sb2Se3 can be used as absorber layer for bifacial solar cells grown on FTO. • Molybdenum promotes high crystalline quality Sb2Se3 with (020) orientation. • Sb2Se3 Ribbon orientation greatly affect the charge collection of the devices. [ABSTRACT FROM AUTHOR]