On the preparation of n-type SnS:Cu using chemical spray pyrolysis for photovoltaic application: Effect of annealing

Thin films of n-type copper doped tin sulfide (SnS:Cu) are deposited employing Chemical Spray Pyrolysis (CSP) technique and effect of post deposition annealing of the films in vacuum as well as in air is evaluated. Structural characterization through X-ray diffraction proved that annealing aided formation of polycrystalline films with orthorhombic structure and preferential orientation of grains along (111) plane, a direction greatly advantageous for PV applications. Raman spectrum of the films had two peaks (at 96 cm−1 and 224 cm−1) belonging only to that of SnS. The band gap of as-prepared films is around ~1.5 eV which changed slightly on annealing. Surface analysis of SnS:Cu films using atomic force microscopy showed the roughness of vacuum annealed samples to be much lower than that of air annealed samples and confirming all the films to be crack free and devoid of pinholes. Chemical analyses with X-ray photoelectron spectroscopy gives the binding energies of Sn3d5/2 at 485.5 eV and S2p3/2 at 161.1 eV, confirming the formation of SnS with Sn2+ and S−2 state. The hot probe measurements revealed their n-type nature, which was affirmed by Hall measurements too. Appreciable hike in conductivity is obtained through Cu-doping; however annealing could not produce any notable effect on conductivity.