Chemical bath deposition of SnS thin films on ZnS and CdS substrates

We illustrate that Tin sulfide (SnS) thin films of 110-500 nm in thickness may be deposited on ZnS and CdS substrates to simulate the requirement in developing window-buffer/SnS solar cells in the superstrate configuration. In the chemical bath deposition reported here, tin chloride and thiosulfate are the major constituents and the deposition is made at 25 A degrees C. In a single deposition, film thickness of 110-170 nm is achieved and in two more successive depositions, the film thickness is 450-500 nm. The thicker films are composed of vertically stacked flakes, 100 nm across and 10-20 nm in thickness. The Sn/S elemental ratio is similar to 1 for the films 110-170 nm in thickness, but it slightly increases for thicker films. The crystalline structure is orthorhombic, similar to the mineral herzenbergite, and with crystallite diameters 13 nm (110-170 films) and 16 nm (450-500 nm films). The Raman bands at 94, 172 and 218 cm(-1) further confirm the SnS composition of the films. The optical band gap of SnS is 1.4-1.5 eV for the thinner films, but is 1.28-1.39 eV for the thicker films, the decrease being ascribed to the increase in the crystallite diameter. Uniform pin-hole free SnS thin films were successfully grown on two different substrates and can be applied in solar cell structures.