Seed Layer Optimisation for Ultra-Thin Sb(2)Se(3) Solar Cells on TiO(2) by Vapour Transport Deposition

Antimony selenide (Sb(2)Se(3)) material has drawn considerable attention as an Earth-abundant and non-toxic photovoltaic absorber. The power conversion efficiency of Sb(2)Se(3)-based solar cells increased from less than 2% to over 10% in a decade. Different deposition methods were implemented to synthesize Sb(2)Se(3) thin films, and various device structures were tested. In search of a more environmentally friendly device composition, the common CdS buffer layer is being replaced with oxides. It was identified that on oxide substrates such as TiO(2) using vacuum-based close-space deposition methods, an intermediate deposition step was required to produce high-quality thin films. However, little or no investigation was carried out using another very successful vacuum deposition approach in Sb(2)Se(3) technology called vapour transport deposition (VTD). In this work, we present optimized VTD process conditions to achieve compact, pinhole-free, ultra-thin (<400 nm) Sb(2)Se(3) absorber layers. Three process steps were designed to first deposit the seed layer, then anneal it and, at the final stage, deposit a complete Sb(2)Se(3) absorber. Fabricated solar cells using absorbers as thin as 400 nm generated a short-circuit current density over 30 mA/cm(2), which demonstrates both the very high absorption capabilities of Sb(2)Se(3) material and the prospects for ultra-thin solar cell application.