Monolithically Integrated BiVO_4/Si Tandem Devices Enabling Unbiased Photoelectrochemical Water Splitting

摘要

A photoelectrochemical (PEC) water splitting device based on a dual-junctionmonolithic tandem cell that utilizes NiOOH/FeOOH/BiVO_4/SnO_2/Ta:SnO_2(TTO)/tunnel oxide passivated contact (TOPCon) Si is reported. The PECdevice achieves a maximum photocurrent density of 1.4 mA cm~(?2) (equal to asolar-to-hydrogen conversion efficiency of 1.72) in 1.0 m potassium boratesolution (pH 9) when illuminated with air mass 1.5 G simulated solarirradiation, which is the highest value among dual-junction monolithicphotoelectrochemical cells except for Ⅲ–Ⅴ materials. The TOPCon Si not onlyworks as an appropriate bottom photoelectrode for subsequenthigh-temperature BiVO4 processing but also offers a high photovoltage of590 mV. Transparent and conductive TTO grown by pulsed laser depositionserves as a recombination layer to achieve effective integration. In addition,the TTO provides chemical and physical protection, allowing the surface ofthe TOPCon Si to exhibit 24 h of tandem cell stability under weak baseelectrolyte conditions. The SnO_2 hole-blocking layer inserted between TTOand BiVO4 enhances the charge separation of BiVO4, allowing the device toachieve high efficiency. Artificial leaf-type monolithic tandem cells consistingof NiFe/BiVO_4/SnO_2/TTO/TOPCon Si/Ag/Ti/Pt with a solar-to-hydrogenefficiency of 0.44 are also demonstrated.