Effect of substrate temperature on the structural optical and electrical properties of new Cu2Cd0.8Mn0.2SnS4 photo-absorber layer for solar cells

We report for the first time the effect of substrate temperature on the structural, optical, and electrical properties of Cu2Cd0.8Mn0.2SnS4 new photovoltaic absorber layer. Cu2Cd0.8Mn0.2SnS4 thin films were deposited on soda lime glass (SLG) substrates by the spray pyrolysis method at different substrate temperatures. X-ray diffraction measurement revealed the formation of cernyite structure by Cu2Cd0.8Mn0.2SnS4 thin film. Also, an increase in crystal size from 7.23 to 14.35 nm and crystallinity improvement of Cu2Cd0.8Mn0.2SnS4 thin film with an increase in substrate temperature were achieved. The atomic force microscopy indicated an increase in surface roughness with substrate temperature. The elemental composition of the Cu2Cd0.8Mn0.2SnS4 thin films showed Cu-poor, S-poor, and Sn-poor conditions. The optical characterization showed that the absorption coefficient of Cu2Cd0.8Mn0.2SnS4 is in the order of 104 cm-1 and the bandgap decreased from 1.89 to 1.87 eV with an increase in substrate temperature. The refractive index dispersion parameters were discussed in terms of the Wemple-Didomenico and Sellmeier equations. Hall effect measurement indicated that the Cu2Cd0.8Mn0.2SnS4 films exhibit P-type conductivity. High hole mobility and the highest conductivity of 2.77 x104 cm2/Vs and 5.60 (Ω.cm)-1 respectively, were achieved at 400 °C substrate temperature. The Cu2Cd0.8Mn0.2SnS4 deposited at 400 °C is a potential candidate for use as a top absorber layer in the tandem solar cell.