the increase in absorption was observed only up to 600 nm and above 600 nm the absorption remains constant indicating that the observed optical changes in the 400–600 nm regions are mainly due only to CdS. As shown in Fig. 2b, an entirely opposite EQE response was noted where the EQE response below 600 nm remain constant while the EQE response above 600 nm increases with the increase of CdS cycles in the PbS/CdS anode for the study of CdS thickness variation while keeping the thickness of PbS at 1 SILAR cycle.