Structure and optical band gap of ZnO1−xSx thin films synthesized by chemical spray pyrolysis for application in solar cells

Highly crystalline c-axis oriented and homogeneous ZnO1−xSx films with sulfur composition 0.05 ≤ x ≤ 0.9 without phase separation were deposited using spray pyrolysis of aqueous precursors. A mechanism of film growth is proposed which envisages a slower kinetics of ZnO precursor decomposition and its specific by-products combined with S-precursor decomposition which enables homogeneous ZnO1−xSx phase formation over a wide S-composition range 0.05 ≤ x ≤ 0.9. This is achieved by controlling the substrate temperature to ≤ 300 °C and the spray rate at ∼ 3 ml/min. The ZnO1−xSx films primarily form by S2− substitution at the O2− lattice sites which is confirmed by detailed analysis of the Zn2p, S2p and O1s x-ray photoelectron spectroscopy peaks. With the increasing of S-content, a structural transformation is observed in ZnO1−xSx films; for x