Renewable energy sources, in particular, photovoltaic solar cells and hydrogen fuel, are expected to be the pillars of a sustainable society. Chalcopyrite CuGaSe2 (CGSe) has potential for using in such applications. This article presents efficient solar cells suitable as top cells for tandem devices and highly active photocathodes for solar hydrogen evolution using CGSe photoabsorber layers with modified p–n heterointerfaces. Rb‐doping during the last stage of CGSe film growth effectively improves the photovoltaic performance, and solar cell efficiency of >10% with a high fill factor (FF) of 74.6% is obtained. The half‐cell solar‐to‐hydrogen conversion efficiency reaches 8% with the use of a photocathode composed of a CGSe film grown in an identical growth batch. Interface modification with i) a Cu‐deficient layer, ii) alkali‐metal doping, and iii) an n‐type buffer layer formed on the CGSe film surface is found to a be key to control the energy conversion device parameters, such as the FF and open circuit voltage of solar cells and the onset potential of photoelectrochemical cells, due to the suppression of interface recombination.

Photoelectrochemical activity for water reduction (H2 liberation) over a co-evaporated CuGaSe2 compact thin film modified with a CdS layer and Pt deposits under simulated sunlight (AM 1.5G) radiation was evaluated, specifically focusing on the impact of a Cu-deficient layer (CDL) loaded on the top part of the CuGaSe2 film. It was found that the intentional loading of the CDL with an appropriate thickness was effective for achieving a large current flow and relatively positive photocurrent onset. The half-cell solar-to-hydrogen efficiency reached 6.6% over the best photocathode used. Moreover, the highest photocurrent onset potential of more than 0.9 V vs reversible hydrogen electrode was achieved over the photocathode based on the CuGaSe2 film having an extremely thick CDL (200 nm) with a relatively thick CdS layer (90 nm) due to efficient spatial separation of photogenerated carriers.

Monoclinic BiVO4 is a promising material for realizing low-cost visible-light water splitting. Here, we report the incorporation mechanism of Zr into solution-processed BiVO4. Characterization of the crystal structure confirmed the incorporation of Zr into the BiVO4 lattice and the formation of single-phase monoclinic crystals at lower Zr concentrations. Characterization of the electronic stucture suggested that Zr acts as a shallow donor indicated that Zr acts as a shallow donor. The Zr-doped sample showed higher electrical conductivity than the undoped one and significantly enhanced photocatalytic activity at an optimum doping level of 0.1 mol %. Characterization of the local structure around Zr by X-ray absorption spectroscopy revealed a Zr4+ center in an 8-coordinated dodecahedral environment, indicating incorporation of Zr as a substitute on Bi site in the BiVO4 host. However, we have found that ZrBi substitution generates local lattice distortion, which, in turn, may cause the formation of more oxygen vacancies (VO) along with ZrBi–VO defect complexes, thus leading to lower Zr donor efficiency and increased nonradiative recombination. High Zr doping provokes the formation of mixed-phase BiVO4 crystals, resulting in low photocatalytic activity. The incomplete self-compensation of Zr in BiVO4 below the solubility limit suggests a potential for substitutional n-type doping of BiVO4 by group IV elements, paving the way for developing efficient BiVO4 based-photocatalytic materials.

We previously reported on a polyhistidine peptide, His16 peptide, as a new cell-penetrating peptide. This peptide is anticipated to be a new carrier for drug delivery systems (DDSs) for targeting intracellular lysosomes because it can transport macromolecules (e.g., liposomes) into these organelles. In the present study, we examined the application of His16 peptide as a DDS carrier against lysosomal storage disease (LSD) cells. LSDs are metabolic disorders caused by loss of specific lysosomal enzymes. For the treatment of LSD cells, we devised a system designated organelle replacement therapy (ORT). ORT is a strategy for transporting exogenous lysosomes containing all kinds of lysosomal enzymes from normal cells into endogenous lysosomes in LSD cells using His16 peptide. To develop the ORT system, we prepared His16 peptide-modified healthy lysosomes (His16-Lyso) by insertion of a stearyl-His16 peptide into a hydrophobic region in the lysosomal membrane. His16-Lyso showed cellular uptake and localization to endogenous lysosomes in LSD cells. His16-Lyso also restored the proliferation of LSD cells, which otherwise showed slower proliferation than normal cells. These results suggested that His16-Lyso replenished deficient lysosomal enzymes in LSD cells. The results further suggest that His16-Lyso are promising candidates as a treatment tool for LSD cells and to establish a foundation for ORT.

Sunlight-induced photoelectrochemical H2 evolution was achived by using a photocathode based on a chalcopyrite CuGaSe2 single crystal.