Antireflective design of Si-based photovoltaics via biomimicking structures on black butterfly scales

Abstract The naturally evolved sunlight harvesters are not limited to foliage. Animals also harvest sunlight for light-heat conversion. A typical antireflective and light-trapping scheme has been well demonstrated on thin butterfly scales where solar energy is converted to heat besides being diffracted for surface coloration. Biomimicking scale structures offers a unique route to enhance light harvesting efficiencies happening on manmade solar cells. Herein, we performed a computational investigation of using microstructures on black butterflies for solar cell efficiency enhancement. Scale microstructures were obtained from nine species of black butterflies and employed as coating structures in numerical models built on Si-slabs. Introducing butterfly wing structures not only reduces the light reflection and transmittance but also increases the light absorption within Si-slabs. Surface reflection was decreased down to 10%, and the short-circuit current was increased by 66% correspondingly. An antireflection design strategy is given and hoped to benefit light harvesting in Si-based solar cells eventually

Dimethylammonium iodide stabilized bismuth halide perovskite photocatalyst for hydrogen evolution

Abstract Metal halide perovskites have emerged as novel and promising photocatalysts for hydrogen generation. Currently, their stability in water is a vital and urgent research question. In this paper a novel approach to stabilize a bismuth halide perovskite [(CH₃)₂NH₂]₃[BiI₆] (DA₃BiI₆) in water using dimethylammonium iodide (DAI) without the assistance of acids or coatings is reported. The DA₃BiI6 powder exhibits good stability in DAI solutions for at least two weeks. The concentration of DAI is found as a critical parameter, where the I- ions play the key role in the stabilization. The stability of DA₃BiI6 in water is realized via a surface dissolution–recrystallization process. Stabilized DA₃BiI₆ demonstrates constant photocatalytic properties for visible light-induced photo-oxidation of I⁻ ions and with PtCl₄ as a co-catalyst (Pt-DA₃BiI₆), photocatalytic H₂ evolution with a rate of 5.7 μmol⋅h-1 from HI in DAI solution, obtaining an apparent quantum efficiency of 0.83% at 535 nm. This study provides new insights on the stabilization of metal halide perovskites for photocatalysis in aqueous solution

Synergistic effect of Ni–Ag–rutile TiO₂ ternary nanocomposite for efficient visible-light-driven photocatalytic activity

Abstract P25 comprising of mixed anatase and rutile phases is known to be highly photocatalytically active compared to the individual phases. Using a facile wet chemical method, we demonstrate a ternary nanocomposite consisting of Ni and Ag nanoparticles, decorated on the surface of XTiO₂ (X: P25, rutile (R)) as an efficient visible-light-driven photocatalyst. Contrary to the current perspective, RTiO₂-based Ni–Ag–RTiO₂ shows the highest activity with the H₂ evolution rate of ∼86 μmol g⁻¹ W⁻¹ h⁻¹@535 nm. Together with quantitative assessment of active Ni, Ag and XTiO₂ in these ternary systems using high energy synchrotron X-ray diffraction, transmission electron microscopy coupled energy dispersive spectroscopy mapping evidences the metal to semiconductor contact via Ag. The robust photocatalytic activity is attributed to the improved visible light absorption, as noted by the observed band edge of ∼2.67 eV corroborating well with the occurrence of Ti³⁺ in Ti 2p XPS. The effective charge separation due to intimate contact between Ni and RTiO₂ via Ag is further evidenced by the plasmon loss peak in Ag 3d XPS. Moreover, density functional theory calculations revealed enhanced adsorption of H₂ on Ti₈O₁₆ clusters when both Ag and Ni are simultaneously present, owing to the hybridization of the metal atoms with d orbitals of Ti and p orbitals of O leading to enhanced bonding characteristics, as substantiated by the density of states. Additionally, the variation in the electronegativity in Bader charge analysis indicates the possibility of hydrogen evolution at the Ni sites, in agreement with the experimental observations