Two-dimensional (2D) halide perovskites have recently been recognized as a promising avenue in perovskite solar cells (PSCs) in terms of encouraging stability and defect passivation effect. However, the efficiency (less than 15%) of ultra-stable 2D Ruddlesden-Popper PSCs still lag far behind their traditional three-dimensional (3D) perovskite counterparts. Here, we report a rationally designed 2D-3D perovskite stacking-layered architecture by in-situ growing 2D PEA 2 PbI 4 capping layers on top of 3D perovskite film, which drastically improved the stability of PSCs without compromising their high performance. Such 2D perovskite capping layer induces larger Fermi-level splitting in the 2D-3D perovskite film under light illumination, resulting in an enhanced open-circuit voltage (V oc ) and thus a higher efficiency of 18.51% in the 2D-3D PSCs. The time-resolved photoluminescence (TRPL) decay measurements indicate the facilitated hole-extraction in the This article is protected by copyright. All rights reserved. 22D-3D stacking-layered perovskite films, which is ascribed to the optimized energy band alignment and reduced non-radiative recombination at the sub gap states. Benefiting from the high moisture resistivity as well as suppressed ion migration of the 2D perovskite, the 2D-3D PSCs show significantly improved long-term stability, retaining nearly 90% of the initial PCE after 1000 h exposure in the ambient conditions with a high relative humidity level of 60±10%.

Photoelectrochemical (PEC) water splitting is a promising approach for solar-driven hydrogen production with zero emissions, and it has been intensively studied over the past decades. However, the solar-to-hydrogen (STH) efficiencies of the current PEC systems are still far from the 10% target needed for practical application. The development of efficient photoelectrodes in PEC systems holds the key to achieving high STH efficiencies. In recent years, crystal facet engineering has emerged as an important strategy in designing efficient photoelectrodes for PEC water splitting, which has yet to be comprehensively reviewed and is the main focus of this article. After the Introduction, the second section of this review concisely introduces the mechanisms of crystal facet engineering. The subsequent section provides a snapshot of the unique facet-dependent properties of some semiconductor crystals including surface electronic structures, redox reaction sites, surface built-in electric fields, molecular adsorption, photoreaction activity, photocorrosion resistance, and electrical conductivity. Then, the methods for fabricating photoelectrodes with faceted semiconductor crystals are reviewed, with a focus on the preparation processes. In addition, the notable advantages of the crystal facet engineering of photoelectrodes in terms of light harvesting, charge separation and transfer, and surface reactions are critically discussed. This is followed by a systematic overview of the modification strategies of faceted photoelectrodes to further enhance the PEC performance. The last section summarizes the major challenges and some invigorating perspectives for future research on crystal facet engineered photoelectrodes, which are believed to play a vital role in promoting the development of this important research field.

Photocatalysis for solar-driven reactions promises a bright future in addressing energy and environmental challenges. The performance of photocatalysis is highly dependent on the design of photocatalysts, which can be rationally tailored to achieve efficient light harvesting, promoted charge separation and transport, and accelerated surface reactions. Due to its unique feature, semiconductors with hollow structure offer many advantages in photocatalyst design including improved light scattering and harvesting, reduced distance for charge migration and directed charge separation, and abundant surface reactive sites of the shells. Herein, the relationship between hollow nanostructures and their photocatalytic performance are discussed. The advantages of hollow nanostructures are summarized as: 1) enhancement in the light harvesting through light scattering and slow photon effects; 2) suppression of charge recombination by reducing charge transfer distance and directing separation of charge carriers; and 3) acceleration of the surface reactions by increasing accessible surface areas for separating the redox reactions spatially. Toward the end of the review, some insights into the key challenges and perspectives of hollow structured photocatalysts are also discussed, with a good hope to shed light on further promoting the rapid progress of this dynamic research field.

Bismuth vanadate (BiVO ) is a promising photoanode material for photoelectrochemical (PEC) water splitting. However, owing to the short carrier diffusion length, the trade-off between sufficient light absorption and efficient charge separation often leads to poor PEC performance. Herein, a new electrodeposition process is developed to prepare bismuth oxide precursor films, which can be converted to transparent BiVO films with well-controlled oxygen vacancies via a mild thermal treatment process. The optimized BiVO film exhibits an excellent back illumination charge separation efficiency mainly due to the presence of enriched oxygen vacancies which act as shallow donors. By loading FeOOH/NiOOH as the cocatalysts, the BiVO dual photoanodes exhibit a remarkable and highly stable photocurrent density of 5.87 mA cm at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination. An artificial leaf composed of the BiVO /FeOOH/NiOOH dual photoanodes and a single sealed perovskite solar cell delivers a solar-to-hydrogen conversion efficiency as high as 6.5% for unbiased water splitting.

BiVO 4 films with (040) facet grown vertically on fluorine doped SnO 2 (FTO) glass substrates are prepared by as eed-assisted hydrothermal method. As imple electrochemical treatment process drastically enhances the photocatalytic activity of BiVO 4 ,e xhibiting ar emarkable photocurrent density of 2.5 mA cm À2 at 1.23 Vv s. reversible hydrogen electrode (RHE) under AM 1.5 Gi llumination, which is approximately 10-fold higher than that of the pristine photoanode.Loading cobalt borate (CoBi)ascocatalyst, the photocurrent density of the BiVO 4 photoanode can be further improved to 3.2 mA cm À2 ,d elivering an applied bias photonto-current efficiency (ABPE) of 1.1 %. Systematic studies reveal that crystal facet orientation also synergistically boosts both charge separation and transfer efficiencies,r esulting in remarkably enhanced photocurrent densities.T hese findings provideafacile and effective approach for the development of efficient photoelectrodes for photoelectrochemical water splitting.