No abstract

The performance of plasmonic Au nanostructure/metal oxide heterointerface shows great promise in enhancing photoactivity, due to its ability to confine light to the small volume inside the semiconductor and modify the interfacial electronic band structure. While the shape control of Au nanoparticles (NPs) is crucial for moderate bandgap semiconductors, because plasmonic resonance by interband excitations overlaps above the absorption edge of semiconductors, its critical role in water splitting is still not fully understood. Here, first, the plasmonic effects of shape-controlled Au NPs on bismuth vanadate (BiVO ) are studied, and a largely enhanced photoactivity of BiVO is reported by introducing the octahedral Au NPs. The octahedral Au NP/BiVO achieves 2.4 mA cm at the 1.23 V versus reversible hydrogen electrode, which is the threefold enhancement compared to BiVO . It is the highest value among the previously reported plasmonic Au NPs/BiVO . Improved photoactivity is attributed to the localized surface plasmon resonance; direct electron transfer (DET), plasmonic resonant energy transfer (PRET). The PRET can be stressed over DET when considering the moderate bandgap semiconductor. Enhanced water oxidation induced by the shape-controlled Au NPs is applicable to moderate semiconductors, and shows a systematic study to explore new efficient plasmonic solar water splitting cells.

Transparent optoelectronics can enable a new class of applications such as transparent displays, smart windows, and invisible sensors. Here, we demonstrate all-transparent NO 2 gas sensors based on aluminum-doped zinc oxide (AZO) freestanding hollow nanofibers. Freestanding AZO nanofibers are fabricated by sputtering AZO on template polyvinylpyrrolidone (PVP) nanofibers, which are electrospun on a glass frame with indium zinc oxide (IZO) transparent electrodes, followed by a heat treatment to remove the PVP template nanofibers. Not only the gas-sensing active material but also other components such as the substrate and electrodes are all transparent in the visible region. The optical transparency of the nanofibers is controlled by changing the AZO nanofibers density without compromising the sensitivity. The gassensing measurements of the transparent sensor depict n-type response behavior with full recovery even at low NO 2 concentrations (0.5 ppm). The high sensitivity of the transparent sensors is attributed to the higher surface area of the hollow nanofibers and the high impact frequency of trapped NO 2 gas inside the hollow compared to solid counterpart nanofibers. The unique combination of transparency and high sensitivity can potentially have applications in advanced sensor systems that can be attached to windows integrated with the Internet of Things.

Well-ordered nanostructure arrays with controlled densities can potentially improve material properties; however, their fabrication typically involves the use of complicated processing techniques. In this work, we demonstrate a uniaxial alignment procedure for fabricating poly(vinylidene fluoride) (PVDF) electrospun nanofibers (NFs) by introducing collectors with additional steps. The mechanism of the observed NF alignment, which occurs due to the concentration of lateral electric field lines around collector steps, has been elucidated via finite-difference time-domain simulations. The membranes composed of well-aligned PVDF NFs are characterized by a higher content of the PVDF β-phase, as compared to those manufactured from randomly orientated fibers. The piezoelectric energy harvester, which was fabricated by transferring well-aligned PVDF NFs onto flexible substrates with Ag electrodes attached to both sides, exhibited a 2-fold increase in the output voltage and a 3-fold increase in the output current as compared to the corresponding values obtained for the device manufactured from randomly oriented NFs. The enhanced piezoresponse observed for the aligned PVDF NFs is due to their higher β-phase content, denser structure, smaller effective radius of curvature during bending, greater applied strain, and higher fraction of contributing NFs.

Transparent solar cells (TSCs) are emerging devices that combine the advantages of visible transparency and light-to-electricity conversion. Currently, existing TSCs are based predominantly on organics, dyes, and perovskites; however, the rigidity and color-tinted transparent nature of those devices strongly limit the utility of the resulting TSCs for real-world applications. Here, we demonstrate a flexible, color-neutral, and high-efficiency TSC based on a freestanding form of n-silicon microwires (SiMWs). Flat-tip SiMWs with controllable spacing are fabricated via deep-reactive ion etching and embedded in a freestanding transparent polymer matrix. The light transmittance can be tuned from ~10 to 55% by adjusting the spacing between the microwires. For TSCs, a heterojunction is formed with a p-type polymer in the top portion of the n-type flat-tip SiMWs. Ohmic contact with an indium-doped ZnO film occurs at the bottom, and the side surface has an Al2O3 passivation layer. Furthermore, slanted-tip SiMWs are developed by a novel solvent-assisted wet etching method to manipulate light absorption. Finite-difference time-domain simulation revealed that the reflected light from slanted-tip SiMWs helps light-matter interactions in adjacent microwires. The TSC based on the slanted-tip SiMWs demonstrates 8% efficiency at a visible transparency of 10% with flexibility. This efficiency is the highest among Si-based TSCs and comparable with that of state-of-the-art neutral-color TSCs based on organic–inorganic hybrid perovskite and organics. Moreover, unlike others, the stretchable and transparent platform in this study is promising for future TSCs.