Synthesis of Cu(In,Ga)S2 nanoparticles via hot-injection method and incorporation with 3D-ZnO/In2S3 heterojunction photoanode for enhanced optical and photoelectrochemical properties

•Chalcopyrite Cu(In,Ga)S2 (CIGS) nanoparticles have been synthesized.•3D-ZnO has been used as the base material for In2S3 and CIGS sensitization.•3D-ZnO/In2S3 photoelectrode generated ~1.1 mA.cm−2 of photocurrent density.•Optical properties have been enhanced with CIGS-Np in between 3D-ZnO and In2S3.•Introducing CIGS-Np between 3D-ZnO NS and In2S3 increased IPCE from 35% to 53.2%. Copper-based ternary Cu(In,Ga)S2 (CIGS) nanoparticles (Np) in chalcopyrite crystal phase have been synthesized via hot-injection method to be used as colloidal Np ink for 3D-ZnO nanosheet thin film sensitization for the enhancement of light absorption in the visible region due to its suitable bandgap. Additionally, an indium sulfide (In2S3) layer has been deposited on the 3D-ZnO/CIGS thin-film for surface modification of CIGS layer to protect against photocorrosion, and bare 3D-ZnO for constructing suitable band alignment in photoelectrochemical water splitting (PEC) applications for hydrogen production. The 3D-ZnO/In2S3 photoelectrode generated the photocurrent density (J) of ~ 1.1 mA.cm−2 (at 1.2 V vs. RHE) and an incident photon to-current efficiency (IPCE) of 35.0% at 382 nm. On the other hand, after incorporation of CIGS-Np between 3D-ZnO NS and In2S3 layers, 2.2 mA.cm−2 of J (at 1.2 V vs. RHE) and 53.2% IPCE at 382 nm have been observed.