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Metal-organic decomposition is an easy way to fabricate BiVO 4 (BVO) photoanodes; however, it often experiences a reproducibility issue. Here, the aging duration of a vanadium precursor solution, vanadyl acetylacetonate in methanol, is identified as a factor that profoundly affects reproducibility. Substantial changes in structural, optical, and electrical properties of BVO films are observed upon varying aging time of vanadium precursor solutions, which subsequently impacts photoelectrochemical (PEC) water oxidation and sulfite oxidation reactions. With the optimum number of aging days (3 d), some deficiency of oxygen is observed, which is accompanied by an increase in carrier concentration and a reduced charge transfer resistance in the PEC device, which produces the highest PEC performance that is comparable to the state-of-the-art undoped BVO photoanodes. The findings point to the importance of understanding solution chemistry and demonstrate that utilization of the understanding of fine adjustment of the composition of BVO films can produce highly reproducible and efficient BiVO 4 photoanodes.

Sb2Se3, a quasi-1D structured binary chalcogenide, has great potential as a solar cell light absorber owing to its anisotropic carrier transport and benign grain boundaries when the absorber layer is...

A tandem photoelectrochemical (PEC) water-splitting device for solar hydrogen production consists of two light absorbers with different bandgaps. It is important to enhance the performance of both cells to achieve...

Cu 2 S is a promising solar energy conversion material due to its suitable optical properties, high elemental earth abundance, and nontoxicity. In addition to the challenge of multiple stable secondary phases, the short minority carrier diffusion length poses an obstacle to its practical application. This work addresses the issue by synthesizing nanostructured Cu 2 S thin films, which enables increased charge carrier collection. A simple solution-processing method involving the preparation of CuCl and CuCl 2 molecular inks in a thiol-amine solvent mixture followed by spin coating and low-temperature annealing was used to obtain phase-pure nanostructured (nanoplate and nanoparticle) Cu 2 S thin films. The photocathode based on the nanoplate Cu 2 S (FTO/Au/Cu 2 S/CdS/TiO 2 /RuO x ) reveals enhanced charge carrier collection and improved photoelectrochemical water-splitting performance compared to the photocathode based on the non-nanostructured Cu 2 S thin film reported previously. A photocurrent density of 3.0 mA cm −2 at −0.2 versus a reversible hydrogen electrode (V RHE ) with only 100 nm thickness of a nanoplate Cu 2 S layer and an onset potential of 0.43 V RHE were obtained. This work provides a simple, cost-effective, and high-throughput method to prepare phase-pure nanostructured Cu 2 S thin films for scalable solar hydrogen production.

A two-step synthesis method involving the electrodeposition of a Bi precursor and drop-casting of a V precursor is widely used to produce highly efficient BiVO 4 photoanodes. This method requires a final etching step to remove excess V 2 O 5 on top of BiVO 4 , and the use of chemical etching with aqueous NaOH solution is the most common. However, there is an issue with the uniformity and reproducibility of BiVO 4 because of local chemical damage to the surface of BiVO 4 during the etching step. Here, we present an electrochemical etching method for selective removal of excess V 2 O 5 without any damage on BiVO 4 , which is based on different stability windows (in terms of pH and bias) of V 2 O 5 and BiVO 4 . In contrast to the conventional chemical etching, continued etching over an optimal time causes no degradation of BiVO 4 films, eliminating the causes of local fluctuation of photoelectrochemical sulfite and water oxidation performance, improving both uniformity and reproducibility. Additionally, through comparative physical and chemical analysis of BiVO 4 prepared by the chemical and electrochemical etching methods, we identified loss of surface V from BiVO 4 as the reason for the performance degradation in excessive chemical etching.

Platinum hydrogen evolution reaction (HER) electrocatalysts in the form of nanocubes (NCs) were synthesized at 50 °C by aqueous‐based colloidal synthesis and were applied to electrochemical (EC) and photoelectrochemical (PEC) systems by a fast and simple drop‐casting method. A remarkable Pt mass activity of 1.77 A mg−1 at −100 mV was achieved in EC systems (fluorine‐doped tin oxide/Pt NC cathode) with neutral electrolyte while maintaining low overpotential and Tafel slope. In the Cu(In,Ga)(S,Se)2 (CIGS)‐based PEC system, a carefully chosen amount of Pt NC loading to achieve a compromise between the catalytic activity (more Pt NCs) and better light transmittance (fewer Pt NCs) led to a maximum onset potential of 0.678 V against the reference hydrogen electrode. The photoelectrodes with Pt NCs also exhibited good long‐term operational stability over 9.5 h with negligible degradation of the photocurrent. This study presents an effective strategy to greatly reduce the use of expensive Pt without compromising the catalytic performance because the drop‐casting of Pt NC solutions to form electrocatalysts is expected to waste less raw material than vacuum deposition.

A photoelectrochemical (PEC) water splitting device based on a dual‐junction monolithic tandem cell that utilizes NiOOH/FeOOH/BiVO4/SnO2/Ta:SnO2 (TTO)/tunnel oxide passivated contact (TOPCon) Si is reported. The PEC device achieves a maximum photocurrent density of 1.4 mA cm−2 (equal to a solar‐to‐hydrogen conversion efficiency of 1.72%) in 1.0 m potassium borate solution (pH 9) when illuminated with air mass 1.5 G simulated solar irradiation, which is the highest value among dual‐junction monolithic photoelectrochemical cells except for III–V materials. The TOPCon Si not only works as an appropriate bottom photoelectrode for subsequent high‐temperature BiVO4 processing but also offers a high photovoltage of 590 mV. Transparent and conductive TTO grown by pulsed laser deposition serves as a recombination layer to achieve effective integration. In addition, the TTO provides chemical and physical protection, allowing the surface of the TOPCon Si to exhibit 24 h of tandem cell stability under weak base electrolyte conditions. The SnO2 hole‐blocking layer inserted between TTO and BiVO4 enhances the charge separation of BiVO4, allowing the device to achieve high efficiency. Artificial leaf‐type monolithic tandem cells consisting of NiFe/BiVO4/SnO2/TTO/TOPCon Si/Ag/Ti/Pt with a solar‐to‐hydrogen efficiency of 0.44% are also demonstrated.