The direct conversion of solar energy into hydrogen represents an attractive but challenging alternative for photo-voltaic solar cells. Several metal oxide semiconductors are able to split water into hydrogen and oxygen upon illumination, but the efficiencies are still (too) low. The operating principles of photo-electrochemical devices for water splitting, their main bottlenecks, and the various device concepts will be reviewed. Materials properties play a key role, and the advantages and pitfalls of the use of interfacial layers and dopants will be discussed. Special attention will be given to recent progress made in the synthesis of nanostructured metal oxides with high aspect ratios, such as nanowire arrays, which offers new opportunities to develop efficient photo-active materials for solar water splitting.

BiVO4 has received much recent interest as a promising photocatalyst for oxygen evolution from water, but little is known about the factors that limit its performance as a photoanode. In this article, we report on highly efficient and reproducible BiVO4 photoanodes prepared by a new spray pyrolysis recipe. For undoped films deposited on a transparent conducting substrate (F-doped SnO2, FTO), electron transport and charge collection at the back-contact were found to limit the photoresponse. Electron transport could be greatly enhanced by donor-doping with 1% W, while the charge collection problem has been solved by introducing a thin (∼10 nm) interfacial layer of SnO2 in between the FTO and the BiVO4. This layer presumably acts as a hole mirror that prevents recombination via FTO-related defect states at the FTO/BiVO4 interface. By addressing these two issues, the external quantum efficiency (IPCE) of spray-deposited BiVO4 films was improved by a factor of ∼7, leading to an unprecedented IPCE of 46% (at 450 nm) at 1.63 VRHE for 1% W-doped BiVO4 films deposited on FTO/SnO2.

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Understanding interfacial loss and the ways to improving interfacial property is critical to fabricate highly efficient and reproducible perovskite solar cells (PSCs). In SnO2‐based PSCs, nonradiative recombination sites at the SnO2–perovskite interface lead to a large potential loss and performance variation in the resulting photovoltaic devices. Here, a novel SnO2‐in‐polymer matrix (i.e., polyethylene glycol) is devised as the electron transporting layer to improve the film quality of the SnO2 electron transporting layer. The SnO2‐in‐polymer matrix is fabricated through spin‐coating a polymer‐incorporated SnO2 colloidal ink. The polymer is uniformly dispersed in SnO2 colloidal ink and promotes the nanoparticle disaggregation in the ink. Owing to polymer incorporation, the compactness and wetting property of SnO2 layer is significantly ameliorated. Finally, photovoltaic devices based on Cs0.05FA0.81MA0.14PbI2.55Br0.45 perovskite sandwiched between SnO2 and Spiro‐OMeTAD layer are fabricated. Compared with the averaging power conversion efficiency of 16.2% with 1.2% deviation for control devices, the optimized devices exhibit an improved averaging efficiency of 19.5% with 0.25% deviation. The conception of polymer incorporation in the electron transporting layer paves a way to further increase the performance of planar perovskite solar cells.

In spite of great progress in the surface modification of semiconductor photoelectrodes, the role of the metal oxide cocatalyst on photoelectrochemical (PEC) performance is still not well understood. In this study, ferrihydrite (Fh) as a novel cocatalyst was decorated on a wormlike nanoporous BiVO4 photoanode. A surface kinetics study of Fh/BiVO4 by intensity-modulated photocurrent spectroscopy (IMPS) evidences the primary role of Fh on PEC performance enhancement, varying with the loading of Fh. It was found that dispersed Fh nanoparticles accelerate hole transfer for water oxidation, but the resulting photoanode suffers from poor stability. The thick layers of Fh address the stability of the electrode by suppressing surface charge recombination but result in reduced hole transfer rates. Modification of a BiVO4 film with optimally thick layers of discrete nanoflakes effectively reduces charge recombination without compromising stability, leading to a high AM 1.5 G photocurrent of 4.78 mA/cm2 at 1.23 V versus the reversible hydrogen electrode and an applied bias photon to current efficiency of 1.81% at 0.61 V. These values are comparable to the best results reported for undoped BiVO4.

By combining supercritical drying technique with AAO template-assisted electrodeposition, noncollapsed, vertically aligned, and free-standing nanowire arrays on a conductive Au film have been fabricated. We also demonstrate that these free-standing nanowire arrays can be feasibly used for fabricating nanowire-based electrically driven devices.

Alloyed ternary CdS(1-x)Se(x) nanowires were synthesized by template-assisted electrodeposition, in which the ratio of S to Se in the nanowires was controlled by adjusting the relative amounts of the starting materials. Higher-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) showed that the alloyed ternary CdS(1-x)Se(x) nanowires are highly crystalline, and no phase-separated Cd was observed in these nanowires. Optical measurements indicated that the band-gap engineering can be realized in these CdS(1-x)Se(x) nanowires through modulating the composition of S and Se. With broadly tunable optical and electrical properties, these alloyed nanowires could be used in color-tuned nanolasers, biological labels, and nanoelectronics.

Indium (In)-based halide perovskites are desirable for next-generation phosphors and emitting devices, due to their broad emission, nontoxicity, and oxidization avoidance capabilities. However, the In-based perovskites always exhibit low external photoluminescence quantum efficiency (PLQE) as a result of their weak light absorption near the corresponding excitation region, and thus, are limited in extended applications. Herein, we have developed an antimony (Sb)-doping strategy to improve the absorption ability of Cs 2 InCl 5 •H 2 O in the ultraviolet region. Excitingly, we obtained a warm-light phosphor with ultrahigh external (internal) PLQE of 72.8% (86.7%). Typically, upon 1.5% Sb doping, the single-crystalline Cs 2 InCl 5 •H 2 O perovskite displayed a stronger warm-light emission at ∼ 610 nm with a large Stokes shift of 295 nm and full width at half maximum (FWHM) of 164 nm. Density functional theory (DFT) calculations revealed that the Sb-doping induced an impurity level in the bandgap, increasing the density of state (DOS), and promoted more carriers into the conduction band maximum. Furthermore, external PLQE from 18% to 59% could be realized in other zero-dimensional In-based perovskites through the same doping strategy.