In the study of thickness variation of CdS, the thickness of PbS was kept at 1 SILAR cycle and 1–3 cycles of CdS were deposited on PbS by SILAR method. As shown in Fig. 2a, CdS absorbs mainly in the visible region up to 600 nm with an absorption threshold around 620 nm while PbS absorbs in the 400–800 nm region while extending its absorption to IR region (around 1200 nm which is not shown in Fig. 2a).