This work presents the development of a novel chalcogenisation process for the fabrication of CuZnSn(S,Se) (CZTSSe or kesterite) based solar cells that enables generating sharp graded anionic compositional profiles with high S content at the top and low S content at the bottom. This is achieved though the optimization of the annealing parameters including the study of several sulphur sources with different predicted reactivity (elemental S, thiourea, SnS and SeS). As a result, depending on the sulphur source employed, devices with superficially localized maximum sulphur content between 50-20 % within the charge depletion zone, and between 10-30 % towards the bulk material are obtained. This complex graded structure is confirmed and characterized by combining multi-wavelength depth-resolved Raman spectroscopy measurements together with in-depth Auger Electron Spectroscopy (AES) and X-Ray Fluorescence (XRF). In addition, the devices fabricated with such graded-band gap absorbers are shown to be fully functional with conversion efficiencies around 9 % and with improved V deficit values that correlate with the presence of a gradient. These results represent one step forward towards anionic band gap grading in kesterite solar cells.