Quantum dot CdS coupled Cd2SnO4 photoanode with high photoelectrochemical water splitting efficiency

Quantum dot (QD) coupled wide band gap semiconductors such as TiO2 and ZnO have shown enhanced photoelectrochemical (in solar cells as well as water splitting) performance due to extended visible light absorption facilitated by QDs, compounded with favourable energetics for charge injection into the conduction band of the host semiconductor. In this work we investigate a new interesting system in this context, namely cadmium tin oxide (Cd2SnO4) coupled with CdS QDs. We find that the Cd2SnO4 photoanode, despite having a similar bandgap to that of CdS (2.2-2.5 eV), exhibits a very large (>40 fold) enhancement in the efficiency only when coupled to CdS QDs. By employing various microstructural, optoelectronic and photoelectrochemical characterization techniques we show that the favourable energetics and charge transport properties of Cd2SnO4 play the most crucial role in the enhancement of the photoelectrochemical performance. Our work suggests that it may be possible to design highly efficient photoelectrochemical systems by tailoring the constitution of nanocomposites based on the relatively less studied ternary oxide-sulphide heterosystems.