High-Performance <i>a</i>‑Si/c-Si Heterojunction Photoelectrodes for Photoelectrochemical Oxygen and Hydrogen Evolution

Amorphous Si (<i>a</i>-Si)/crystalline Si (c-Si) heterojunction (SiHJ) can serve as highly efficient and robust photoelectrodes for solar fuel generation. Low carrier recombination in the photoelectrodes leads to high photocurrents and photovoltages. The SiHJ was designed and fabricated into both photoanode and photocathode with high oxygen and hydrogen evolution efficiency, respectively, by simply coating of a thin layer of catalytic materials. The SiHJ photoanode with sol–gel NiO_<i>x</i> as the catalyst shows a current density of 21.48 mA/cm² at the equilibrium water oxidation potential. The SiHJ photocathode with 2 nm sputter-coated Pt catalyst displays excellent hydrogen evolution performance with an onset potential of 0.640 V and a solar to hydrogen conversion efficiency of 13.26%, which is the highest ever reported for Si-based photocathodes

Engineering Light Outcoupling in 2D Materials

When light is incident on 2D transition metal dichalcogenides (TMDCs), it engages in multiple reflections within underlying substrates, producing interferences that lead to enhancement or attenuation of the incoming and outgoing strength of light. Here, we report a simple method to engineer the light outcoupling in semiconducting TMDCs by modulating their dielectric surroundings. We show that by modulating the thicknesses of underlying substrates and capping layers, the interference caused by substrate can significantly enhance the light absorption and emission of WSe₂, resulting in a ∼11 times increase in Raman signal and a ∼30 times increase in the photoluminescence (PL) intensity of WSe₂. On the basis of the interference model, we also propose a strategy to control the photonic and optoelectronic properties of thin-layer WSe₂. This work demonstrates the utilization of outcoupling engineering in 2D materials and offers a new route toward the realization of novel optoelectronic devices, such as 2D LEDs and solar cells

Realizing High-Efficiency Omnidirectional n‑Type Si Solar Cells <i>via</i> the Hierarchical Architecture Concept with Radial Junctions

Hierarchical structures combining micropyramids and nanowires with appropriate control of surface carrier recombination represent a class of architectures for radial p-n junction solar cells that synergizes the advantageous features including excellent broad-band, omnidirectional light-harvesting and efficient separation/collection of photoexcited carriers. The heterojunction solar cells fabricated with hierarchical structures exhibit the efficiency of 15.14% using cost-effective as-cut Czochralski n-type Si substrates, which is the highest reported efficiency among all n-type Si nanostructured solar cells. We also demonstrate the omnidirectional solar cell that exhibits the daily generated power enhancement of 44.2% by using hierarchical structures, as compared to conventional micropyramid control cells. The concurrent improvement in optical and electrical properties for realizing high-efficiency omnidirectional solar cells using as-cut Czochralski n-type Si substrates demonstrated here makes a hierarchical architecture concept promising for large-area and cost-effective mass production