Incorporation of Perovskite Quantum Dot Passivated by Ultrathin SiO2 on WO3 for Boosting Solar Water Splitting
Authors: Hong Won Tae , Baeck Unbeom , Kim Jung Kyu 
Published: August 2024

Photoelectrochemical (PEC) water splitting stands as a promising strategy for sustainable hydrogen (H2) production, driven by renewable solar energy conversion. However, the lack of highly efficient photoanodes has constrained high-performance PEC water splitting due to poor light absorption, charge transportation, and sluggish catalytic kinetics of the oxygen evolution reaction (OER). Extensive efforts have focused on developing transition metal oxide (TMO)-based semiconductors as highly efficient photoanodes, owing to their favorable band structure, eco-friendliness, abundance on Earth, and good stability in aqueous environments. However, TMO-based materials encounter challenges such as undesired rapid charge recombination, insufficient surficial reaction kinetics, and low light absorption coefficients. To address these limitations, a systematic design of heterostructured TMO-based photoanodes has been considered a potential strategy. On the other hand, lead halide perovskite quantum dots (PQDs), including all-inorganic CsPbX3 (where X represents one of the halogens), have been extensively investigated for optical energy conversion systems due to their high absorption coefficient, defect tolerance, moderate carrier mobility, and cost-effective preparation. However, the significant instability of PQDs against polar solvents, even under anodic reaction conditions, leading to critical self-oxidation and deformation, has hindered their practical application in solar water splitting. To overcome these restrictions, numerous investigations have explored methods such as encapsulation, ligand modification, and surface engineering to prevent PQD decomposition and modulate charge dynamics based on interfacial characteristics. Constructing a core-shell structure for PQDs with an oxide-based passivation layer has been proposed as an efficient approach to protect PQDs from water molecules and tune the dynamics of photogenerated charges. However, charge extraction from PQDs could be hindered by the high dielectric properties of the oxide-based passivation layer. Thus, a conformal and sub-nanometer scale introduction of the passivation layer can facilitate successful PQD incorporation on TMO-based photoanodes. In this study, we propose a rational heterostructured photoanode for boosting solar water splitting, and we report for the first time that PQDs exposed to an aqueous electrolyte demonstrate excellent stability even under oxidation reaction conditions. We demonstrate a core-shell structured CsPbBr3 PQDs with an ultrathin SiO2 passivation layer (CS-PQDs), less than 1 nm thick, incorporated on a WO3 nanoflake photoanode (CS-PQD/WO3). The SiO2 passivation prevents undesirable recombination of CsPbBr3, and the extraction of photogenerated charges is prominently promoted, indicating not only improved stability of CsPbBr3 PQDs but also manipulated charge dynamics of the CS-PQD/WO3 photoanode. The heterostructured photoanode achieves a 2.2-fold improvement in photocurrent density at 1.23 V versus the reversible hydrogen electrode (RHE) under 1 sun illumination, attributed to enhanced interfacial catalytic kinetics with improved light harvesting and efficient charge migration facilitated by the built-in electric field. Additionally, the CS-PQD/WO3 exhibits moderate durability over 12 hours and excellent Faraday efficiency for H2 production through solar water splitting. This study provides insight into the rational heterostructure of PQDs and TMO, in the presence of an ultrathin oxide passivating layer, raising the potential of perovskite-based nanomaterials as a facilitator for manipulating photogenerated charge dynamics for solar energy conversion in aqueous media.