MgCl2 activation of CdS films: An alternative for CdCl2

•Environmental friendly, non-toxic Cl activation using MgCl2 on CdS thin films is reported.•MgCl2 treatment passivates grain boundaries and improves the carrier concentration and effective surface area of CdS.•Increasing duration of MgCl2 treatment leads to formation of large and densely packed grain surfaces.•PEC cell parameters; VOC and ISC of MgCl2 treated films were higher than untreated CdS films.