Halide perovskite stabilized in a photoelectrochemical environment by impermeable single crystal TiO2 for semi-artificial photosynthesis

Abstract

A photoelectrochemical (PEC) device induces electrochemical reactions on the surfaces of light-absorbing semiconductors to harness sunlight for producing valuable chemicals. The most critical issue in PEC devices is the poor stability of semiconductors in electrochemical environments. The stability can be enhanced by applying a transparent and conductive protection layer, which is usually prepared by an oxide thin film with tens of nanometers, on the semiconductor. Nevertheless, ensuring complete impermeability to an electrolyte remains a significant challenge because even a single pinhole in the thin film can lead to the dissolution of the entire underlying semiconductor layer. In this study, we present a facile and reliable protection method applicable to various semiconductors using a thick (200–500 μm) single crystal of TiO₂. The impermeability is ensured by the exceptionally high thickness, without compromising the device performance. We applied the protection layer on a halide perovskite semiconductor well-known for moisture instability, and inductively coupled plasma mass spectrometry rigorously confirmed that there was no dissolution of elements from the halide perovskite film. The robust protection layer also enabled the safe integration of the halide perovskite PEC device and a biocatalyst without concerns about Pb or halide toxicity. An old yellow enzyme from Thermus scotoductus (TsOYE) coupled with the PEC device enabled the trans-hydrogenation of the CC bonds, demonstrating the expanded applicability and economic potential of PEC systems for producing fine chemicals and pharmaceutical intermediates.