Silicon-based spectrally selective emitters with good high-temperature stability on stepped metasurfaces.

Solar thermophotovoltaic (STPV) systems have attracted increasing attention due to their great prospects for breaking the Shockley-Queisser limit. As a critical component of high-performance STPV systems, fabrication of a spectrally selective emitter with good stability at high temperature is one of the main research challenges. In this study, we developed a hybrid silicon-based metasurface emitter with spectral selectivity and high temperature stability using a simple fabrication process by introducing a controlled silicon nitride (SiNx) layer on a silicon stepped nanopillar substrate coated with molybdenum (Mo). Owing to the cooperative effect of cavity mode resonance and the interference effect of the SiNx dielectric layer, our proposed silicon-based metasurface emitter achieves a broadband optical absorption of ∼95% in the wavelength range of 220-2000 nm, while effectively suppressing the heat radiation to ∼19% in the long wavelength range (>5 µm). Moreover, polarization-independence and angle-insensitivity behaviors are demonstrated in the emitters. Additionally, due to the presence of a SiNx protection layer, this silicon-based metasurface emitter is experimentally proved to sustain its excellent spectral properties after ultra-high temperature treatments, including annealing at 1273 K under an Ar atmosphere for 6 h, even at 1073 K in air for 1 h, which makes it an alternative candidate for application in actual STPV systems.

Enhanced photoluminescence of CsPbBr3-xIx nanocrystals via plasmonic Au nanoarrays.

Large scale ordered Au nanoarrays are fabricated by nanosphere lithography technique. The photoluminescence improvement of CsPbBr3-xIx nanocrystals by more than three times is realized in the CsPbBr3-xIx nanocrystal/Au nanoarray/Si structure. Time-resolved photoluminescence decay curves indicate that the lifetime is decreased by introducing the Au nanoarrays, which results in a increasing radiation recombination rate. The reflection spectra with two major valleys (the dip in the curve) located at ∼325 nm and 545 nm of Au nanoarray/Si structure, which illustrates two plasmonic resonance absorption peaks of the Au nanoarrays. The enhancement of photoluminescence is ascribed to a well match between the excitation/emission of CsPbBr3-xIx nanocrystals and localized surface plasmon/gap plasmon resonance absorption of the ordered Au nanoarrays, as also revealed from the finite-difference time-domain simulation analysis. Our work offers an effective strategy to improve the fluorescence of perovskite nanocrystals and provide the potential for further applications.

Multiple channels to enhance near-infrared emission from SiO2-SnO2:Er3+ films by Ba2+ ion doping.

Ba2+ ions co-doped SiO2-SnO2:Er3+ thin films are prepared using a sol-gel method combined with a spin-coating technique and post-annealing treatment. The influence of Ba2+ ion doping on the photoluminescence properties of thin films is carefully investigated. The enhancement of near-infrared (NIR) emission of Er3+ ions by as much as 12 times is obtained via co-doping with Ba2+ ions. To illustrate the relevant mechanisms, X-ray diffraction, X-ray photoelectron spectroscopy and comprehensive spectroscopic measurements are carried out. The enhanced NIR emission induced by Ba2+ co-doping can be explained by more oxygen vacancies, improved crystallinity and strong cross-relaxation processes between Er3+ ions. The incorporation of Ba2+ ions into SiO2-SnO2:Er3+ thin films results in a considerable enhancement in the NIR emission, making the thin films more suitable for Si-based optical lasers and amplifiers.

Tunable Narrowband Silicon-Based Thermal Emitter with Excellent High-Temperature Stability Fabricated by Lithography-Free Methods.

Thermal emitters with properties of wavelength-selective and narrowband have been highly sought after for a variety of potential applications due to their high energy efficiency in the mid-infrared spectral range. In this study, we theoretically and experimentally demonstrate the tunable narrowband thermal emitter based on fully planar Si-W-SiN/SiNO multilayer, which is realized by the excitation of Tamm plasmon polaritons between a W layer and a SiN/SiNO-distributed Bragg reflector. In conjunction with electromagnetic simulations by the FDTD method, the optimum structure design of the emitter is implemented by 2.5 periods of DBR structure, and the corresponding emitter exhibits the nearly perfect narrowband absorption performance at the resonance wavelength and suppressed absorption performance in long wave range. Additionally, the narrowband absorption peak is insensitive to polarization mode and has a considerable angular tolerance of incident light. Furthermore, the actual high-quality Si-W-SiN/SiNO emitters are fabricated through lithography-free methods including magnetron sputtering and PECVD technology. The experimental absorption spectra of optimized emitters are found to be in good agreement with the simulated absorption spectra, showing the tunable narrowband absorption with all peak values of over 95%. Remarkably, the fabricated Si-W-SiN/SiNO emitter presents excellent high-temperature stability for several heating/cooling cycles confirmed up to 1200 K in Ar ambient. This easy-to-fabricate and tunable narrowband refractory emitter paves the way for practical designs in various photonic and thermal applications, such as thermophotovoltaic and IR radiative heaters.

High efficiency organic-Si hybrid solar cells with a one-dimensional CdS interlayer.

A carrier-selective passivating contact is one of the main factors for the preparation of high-efficiency solar cells. In this work, a one-dimensional nanostructured CdS material combined with quasi-metallic TiN exhibits excellent contact performance with n-Si. In addition, the introduction of the CdS nanowire interlayer is more conducive to the extraction and transmission of electrons, which is attributed to a more suitable energy level alignment between the rear contact and the n-Si absorption layer. As a result, the power conversion efficiency of organic/Si solar cells based on the CdS NW/TiN/Al electron selective passivating contact exceeds 14.0%. This shows a promising technique to achieve high-performance and low-cost photovoltaic devices.

Enhanced Broadband Plasmonic Absorbers with Tunable Light Management on Flexible Tapered Metasurface.

The growing attention in solar energy has motivated the development of highly efficient solar absorbers, and a metasurface absorber with broadband optical absorption is one of the main research interests. In this study, we developed an efficient metasurface absorber on a flexible film with a simple fabrication process. It consists of a polyimide nanocone substrate coated with gold and tungsten layers, exhibiting over 96% optical absorption in the visible range and a tunable absorption performance in the long wave range. From the analysis of experiment and simulation, the enhanced optical absorption is attributed to the synergistic effects of localized nanoparticle plasmon resonance and cavity plasmon resonance, and tunable light management comes from the strong infrared reflection of a gold layer and intrinsic absorption of variable tungsten layers. Meanwhile, the polarization-independent and omnidirectional optical absorption properties are demonstrated in the fabricated absorbers. Furthermore, this absorber shows the robustness against bending, maintaining the stable and excellent absorption performance after hundreds of bending tests. Our work offers a low-cost and straightforward tactic to design and fabricate flexible solar absorbers, and this metasurface absorber is a promising candidate for many exciting applications, such as emissivity control and flexible energy-related devices.

Room-temperature valleytronic transistor.

Valleytronics, based on the valley degree of freedom rather than charge, is a promising candidate for next-generation information devices beyond complementary metal-oxide-semiconductor (CMOS) technology1-4. Although many intriguing valleytronic properties have been explored based on excitonic injection or the non-local response of transverse current schemes at low temperature4-7, demonstrations of valleytronic building blocks similar to transistors in electronics, especially at room temperature, remain elusive. Here, we report a solid-state device that enables a full sequence of generating, propagating, detecting and manipulating valley information at room temperature. Chiral nanocrescent plasmonic antennae8 are used to selectively generate valley-polarized carriers in MoS2 through hot-electron injection under linearly polarized infrared excitation. These long-lived valley-polarized free carriers can be detected in a valley Hall configuration9-11 even without charge current, and can propagate over 18 µm by means of drift. In addition, electrostatic gating allows us to modulate the magnitude of the valley Hall voltage. The electrical valley Hall output could drive the valley manipulation of a cascaded stage, rendering the device able to serve as a transistor free of charge current with pure valleytronic input/output. Our results demonstrate the possibility of encoding and processing information by valley degree of freedom, and provide a universal strategy to study the Berry curvature dipole in quantum materials.

Low power consumption light emitting device containing TiO2:Er3+ thin film prepared by sol-gel method.

Er3+ ions doped titanium dioxide (TiO2) thin films have been prepared by sol-gel method. The photoluminescence both in visible light range (510-580 nm and 640-690 nm) and near infrared light range (1400-1700nm) have been observed. The photoluminescence excitation spectra demonstrate that energy transfer from wide band-gap TiO2 to Er3+ ions causes the infrared light emission. It is also found that the post annealing temperature can influence the luminescence intensity significantly. Based on sol-gel prepared TiO2:Er3+ thin films, we fabricate light emitting device containing ITO/TiO2:Er3+/SiO2/n+-Si/Al structure. Both the visible and near infrared electroluminescence (EL) can be detected under the operation voltage as low as 5.6 V and the working current of 0.66 mA, which shows the lower power consumption compared with the conventional EL devices.

High-temperature stable plasmonic and cavity resonances in metal nanoparticle-decorated silicon nanopillars for strong broadband absorption in photothermal applications.

Plasmonic metal nanoparticles in conjunction with the cavity mode resonance in crystalline silicon (c-Si) nanopillars (NPs) can help achieve strongly enhanced broadband light absorption far beyond the limit of bulk c-Si. However, a major concern arises from the stability of metal nanoparticles, particularly at a high temperature, as the diffusion and conglomeration of the nanoparticles will undermine the very basis for the advantageous plasmonic effect. We here carried out a systematic investigation of the thermal stability of different metal nanoparticles coated on 3D Si-based NPs and found that simple Al2O3 encapsulation could help stabilize the gold (Au) particles coated on Si NPs even when subjected to annealing at >1073 K while accomplishing excellent broadband optical absorption (∼95%) from 200 nm to 2500 nm. This could be assigned mainly to the excellent dispersion retention capability of the Al2O3-encapsulated Au nanoparticles and the beneficial plasmon resonance absorption among the Au nanoparticles and Si NPs, as also revealed from the FDTD simulation analysis. Finally, a rapid vapor generation application was demonstrated based on the optimized Au/Si NPs, where salt water drops could be directly injected onto the high-temperature photo-heated Au/Si NPs and could vaporize/bounce off quickly without leaving any salt precipitation on the surface. This new strategy can also pave the way for high-performance Si-based photothermal applications.