Introducing a zinc stannate, ZnSnO3 (ZTO), layer on hydrothermally grown 3D-zinc oxide (ZnO) nanosheet thin films has been proven to have a quenching effect on the photoluminescence emissions, indicating very slow recombination of photoinduced electron–hole pairs in photoelectrochemical water splitting (PEC) reactions. Motivated by this, the ZnO/ZTO bilayer system has been used as the electron transport layer for copper indium gallium sulfide (CIGS)-based photoelectrodes in PEC applications. Furthermore, the poor photoresistivity of CIGS has been improved via indium sulfide (In2S3) deposition. Consequently, the photoelectrode obtained from the inverted configuration, ZnO/ZTO/CIGS/In2S3, has generated a photocurrent density of 6.4 mA cm–2 at 0.4 V (vs Ag/AgCl), exceeding the performance of ZnO NS/CIGS/In2S3 photoelectrodes by three folds. The highest ABPE and IPCE efficiencies have been calculated as 4.2% and 57%, respectively. More importantly, two cost-effective nonvacuum techniques for large-scale thin film fabrications such as chemical bath deposition (CBD) and ultrasonic spray pyrolysis (USP) methods have been adopted to acquire photoelectrodes with inverted configurations providing an advantageous approach for low-cost photoelectrode design for sustainable energy production.

The utilization of indium sulfide (In 2 S 3 ) photoelectrodes in an all-vanadium photoelectrochemical redox flow battery system has been investigated. The In 2 S 3 -based photoelectrodes have been prepared via the ultrasonic spray pyrolysis (USP) method. The thickness of the In 2 S 3 photoelectrodes has been altered via increasing the pass number of the USP nozzle from 25 to 75 passes. Each pass delivers 6 μL•cm −2 of the precursor solution. Within the scope of the photoelectrochemical oxidation on the In 2 S 3 , the vanadium couples of VO 2+ /V 3+ have been proven to be promising redox species. The maximum charge separation and quantum efficiencies of 46% and 20% have been calculated, respectively.

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