BiVO/CsPtI Vacancy-Ordered Halide Perovskite Heterojunction for Panchromatic Light Harvesting and Enhanced Charge Separation in Photoelectrochemical Water Oxidation.

Photoelectrochemical water oxidation is a challenging reaction in solar water splitting due to the parasitic recombination process, sluggish catalytic activity, and electrode stability. Oxide semiconductors are stable in an aqueous medium but show huge charge carrier recombination. Creation of a heterojunction is found to be effective for extracting the photogenerated electrons/holes before they recombine to the ground state. In this work, we created a heterojunction of BiVO with vacancy-ordered halide perovskite CsPtI and used it as a photoanode in PEC water oxidation. CsPtI is the only halide perovskite that is found to be extremely stable even in strong acids and bases. We utilized the stability of this material and its panchromatic visible light absorption property and made the first unprotected heterojunction dual-absorber photoanode for PEC water oxidation. At 1.23 V (vs RHE), bare BiVO gave 0.6 mA cm photocurrent density, whereas the BiVO/CsPtI heterojunction shows 0.92 mA cm. With the addition of IrO cocatalyst, at 1.23 V (vs RHE), the heterojunction gave ∼2 mA cm. To obtain 2 mA cm photocurrent, pure BiVO requires 560 mV overpotential, whereas the heterojunction requires 250 mV. The increase in the photocurrent arises from the increase in the efficiency of charge separation from BiVO to CsPtI and the complementary absorption offered by the latter.