Monolithically Integrated BiVO4/Si Tandem Devices Enabling Unbiased Photoelectrochemical Water Splitting

A photoelectrochemical (PEC) water splitting device based on a dual-junction monolithic tandem cell that utilizes NiOOH/FeOOH/BiVO4/SnO2/Ta:SnO2 (TTO)/tunnel oxide passivated contact (TOPCon) Si is reported. The PEC device achieves a maximum photocurrent density of 1.4 mA cm(-2) (equal to a solar-to-hydrogen conversion efficiency of 1.72%) in 1.0 m potassium borate solution (pH 9) when illuminated with air mass 1.5 G simulated solar irradiation, which is the highest value among dual-junction monolithic photoelectrochemical cells except for III-V materials. The TOPCon Si not only works as an appropriate bottom photoelectrode for subsequent high-temperature BiVO4 processing but also offers a high photovoltage of 590 mV. Transparent and conductive TTO grown by pulsed laser deposition serves as a recombination layer to achieve effective integration. In addition, the TTO provides chemical and physical protection, allowing the surface of the TOPCon Si to exhibit 24 h of tandem cell stability under weak base electrolyte conditions. The SnO2 hole-blocking layer inserted between TTO and BiVO4 enhances the charge separation of BiVO4, allowing the device to achieve high efficiency. Artificial leaf-type monolithic tandem cells consisting of NiFe/BiVO4/SnO2/TTO/TOPCon Si/Ag/Ti/Pt with a solar-to-hydrogen efficiency of 0.44% are also demonstrated.

Automated summary

A photoelectrochemical water splitting device based on a dual-junction monolithic tandem cell with high performance was developed. The device achieved the highest photocurrent density and solar-to-hydrogen conversion efficiency among dual-junction monolithic photoelectrochemical cells, except for III-V materials. The use of TOPCon Si, TTO and SnO2 in the device contributed to its stability and high efficiency.