Thin films of p-SnS and n-Sn2S3 for solar cells produced by thermal processing of chemically deposited SnS

Abstract

Post-deposition heat treatments of chemically deposited SnS-orthorhombic thin films at 450 °C in a controlled ambient greatly influence their structural, morphological, compositional, optical and electrical properties. Heating of the film with a tin chloride layer (90 nm in thickness) produced by thermal evaporation led to an increased crystalline grain diameter (23 nm) in the film, with characteristics suitable for solar cell application: a bandgap (Eg) of 1.2 eV (indirect), p-type electrical conductivity of 10–3 Ω–1 cm–1, hole concentration of 1015 cm–3 and hole mobility of 2.4 cm2/(V s). However, heating the SnS film in a controlled S-vapour ambient converted it to Sn2S3 with a crystalline grain diameter of 24 nm, Eg of 1.2 eV (direct), n-type electrical conductivity of 3.4 × 10–3 Ω–1 cm–1, and an electron concentration of 1016 cm–3. Optical absorption spectra of these materials suggest a photo-generated current density (JL) of 32 mA/cm2 under air mass 1.5 Global (1000 W/m2) solar radiation for either material for a thickness of 600 nm, which is attractive for solar cells.