The current strategies in the development of Sb2Se3 thin film solar cells involve fabrication and optimization ofsuperstrate and substrate device architectures, with the preferable choice for TiO2 and CdS heterojunction layers.For CdS-based superstrate cells, several studies reported the necessity to apply CdCl2 or other metal halide-basedpost-deposition treatment (PDT), highlighting improvement of CdS/Sb2Se3 device efficiency. However, the need,effect, and mechanism of such PDT are very often not described. Additionally, the fact that many groups have notsucceeded in demonstrating its benefits suggests that this strategy is not straightforward, requiring a deeperunderstanding towards a more unified concept. The present study proposes an alternative approach to thechallenging CdCl2 PDT of CdS in CdS/Sb2Se3 device, involving controllable Cl incorporation in CdS films bysystematically varying the concentration of NH4Cl in the CBD precursor solution from 1 to 8 mM. Structural andelectrical characterizations are correlated with advanced measurements of Scanning Kelvin Probe, surfacephotovoltage, and atomic force microscopy to understand the impact of Cl incorporation on the properties of CdSfilms and CdS/Sb2Se3 devices. The validity of Cl incorporation in the CdS lattice and interdiffusion processes atthe CdS-Sb2Se3 interface is confirmed by secondary ion mass spectrometry analysis. It is demonstrated thatincorporation of 1 mM of NH4Cl, as a Cl source in CBD CdS, can boost the PCE of CdS/Sb2Se3 by ~20 %. With thisapproach, we offer new perspectives on the optimization methodology for Cl-based CdS/Sb2Se3 device processingand complementary understanding of the physiochemistry behind these processes.