CeO-CuInS2 nanocomposite as an efficient absorber layer for high-performance thin film solar cells: structural, optical, and photovoltaic investigation

The relatively low photovoltaic efficiency of CuInS 2 absorber layers, caused by severe charge-carrier recombination and inefficient interfacial charge transport, remains a major challenge for thin-film solar cells. In this work, a CeO–CuInS 2 heterostructure absorber was synthesized via a hydrothermal approach to enhance charge separation and carrier transport. X-ray diffraction confirmed the coexistence of tetragonal CuInS 2 and cubic CeO phases with high crystallinity and an average crystallite size of 34.8 nm. Raman spectroscopy verified structural integrity through characteristic A 1 and F 2 g vibrational modes, while SEM revealed a porous cauliflower-like morphology favorable for light harvesting. HR-TEM analysis demonstrated well-defined lattice fringes with an interplanar spacing of 3.217 Å, indicating excellent crystallinity. Optical investigations showed a red-shifted absorption edge and a reduced bandgap from 2.22 to 2.09 eV, enhancing visible-light absorption. Photoluminescence measurements evidenced suppressed electron–hole recombination owing to efficient interfacial charge separation. The fabricated FTO/TiO 2 /CeO–CuInS 2 /Spiro-OMeTAD/Au device achieved a V oc of 0.733 V, J sc of 13.82 mA cm −2 , FF of 0.62, and PCE of 6.29%, outperforming pristine CuInS 2 . EIS and EQE analyses further confirmed reduced charge-transfer resistance, suppressed recombination, and enhanced carrier collection efficiency. These findings demonstrate that CeO incorporation is an effective strategy for improving CuInS 2 -based absorber layers for high-performance thin-film solar cells.