Photoelectrochemical Water-Splitting Device Based on a Halide Perovskite Solar Cell Protected by a Single Crystal TiO₂

Photoelectrochemical (PEC) water splitting is a renewable way to produce hydrogen by introducing electrocatalysts on the surface of photovoltaic materials. Compared to a system electrically connecting separate photovoltaic and electrochemical devices, PEC has a simpler structure because it can remove peripheral components (e.g. Ag metal grid or power electronics) and it may lead to a significant reduction in system cost and efficiency loss. However, one of the greatest challenges in PEC is that light-absorbing materials are in contact with (or in the vicinity of) electrolytes, and it would cause severe damage to the light-absorbing materials. This issue becomes more serious when it comes to a halide perovskite light absorber. The halide perovskite solar cell is an emerging photovoltaic material with great potential, however, because of its instability when in contact with water or oxygen, PEC devices forming a solid-liquid junction between halide perovskites and electrolytes have been showing poor stabilities. A typical approach to protect a PEC device is depositing a protection layer with a tens or hundreds nanometer thickness over the light-absorbing materials, however, a protection layer completely impermeable to an electrolyte has not been demonstrated yet. Furthermore, processing for protection layer deposition often requires a high temperature, which is not applicable to thermally vulnerable halide perovskite materials. For these reasons, PEC devices based on halide perovskites have been showing only several hours of device lifetime.<br/>In this study, we improve the stability of a perovskite PEC device by transferring a single crystal TiO₂ wafer (1cmX1cm) onto a halide perovskite cell. In order to form an ohmic contact on a TiO₂ wafer, indium tin oxide (ITO) was deposited on one side, while the other side was decorated with Pt for catalyzing hydrogen evolution reaction. The TiO₂ wafer was transferred onto a halide perovskite solar cell by bridging the perovskite cell and ITO contact with a transparent conductive adhesive, which is prepared by embedding Ag particles into paraffin. The PEC device showed an open circuit potential of ~1.1 V and short-circuit current density of ~14 mA/cm², and was able to operate for ~2 days without degradation in current density.