Visible light active CZTS sensitized CdS/TiO2 tandem photoanode for highly efficient photoelectrochemical hydrogen generation

A tandem photoanode consisting of Cu2ZnSnS4 (CZTS) nanoparticles layer over CdS/TiO2 heterostructure thin film on FTO substrate has been fabricated for photoelectrochemical hydrogen generation. CdS thin film has been deposited by chemical bath deposition over the spin-coated TiO2 thin film, which is followed by the deposition of CZTS nanoparticles layer by spray coating technique resulting in a CZTS/CdS/TiO2/FTO photoanode. The coating of CZTS nanoparticles layer over CdS/TiO2 films resulted in the tandem structure of different band level positions, which enhances the optical absorption in the visible region and also leads to higher separation of the photogenerated charge carriers. A substantial enhancement (39 times) in the PEC activity has been demonstrated for the CZTS/CdS/TiO2/FTO photoanode as compared to TiO2/FTO photoanode, which is due to cascade band gap from 3.2 eV to 1.7 eV and formation of heterojunction at interfaces. The enhancement in the charge transport properties of CZTS/CdS/TiO2/FFO photoanode has been confirmed from the electrochemical impedance spectroscopy (EIS) measurement. The EIS results confirm that the CZTS/CdS/TiO2/FTO photoanode exhibited lowest charge transfer resistance (R-ct = 302 Omega/cm(2)) as compared to CdS/TiO2 (R-ct = 615 Omega/cm(2)) and TiO2 (R-ct = 1700 Omega/cm(2)) photoanode. A mechanism depicting the enhanced the performance of photoelectrochemical (PEC) CZTS/CdS/TiO2/FTO photoanode has been proposed.