Spray-pyrolysed zinc oxy-sulphide Zn(O,S) has been doped with varying concentrations of indium (In) toimprove its electrical and optical properties for possible application as buffer layer in thin film solar cells. The In-dopingin Zn(O,S) is found to change the electron carrier concentration from 10$^{19}$ to 10$^{18}$ cm$^{−3}$ and a subsequent annealing in argon atmosphere is found to improve its electrical conductivity. Moreover, annealing in air atmosphere reduces the carrier concentration to a range of 10$^{13}$–10$^{15}$ cm$^{−3}$ making it useful as a buffer layer. The reduction in degeneracy of In-doped Zn(O,S) is desirable for its application as buffer material, whereas annealing in argon makes it suitable as electron membrane (window layer) in thin film solar cell.