Observation of Transparency of Erbium-doped Silicon nitride in photonic crystal nanobeam cavities

One-dimensional nanobeam photonic crystal cavities are fabricated in an Er-doped amorphous silicon nitride layer. Photoluminescence from the cavities around 1.54 um is studied at cryogenic and room temperatures at different optical pump powers. The resonators demonstrate Purcell enhanced absorption and emission rates, also confirmed by time-resolved measurements. Resonances exhibit linewidth narrowing with pump power, signifying absorption bleaching and the onset of stimulated emission in the material at both 5.5 K and room temperature. We estimate from the cavity linewidths that Er has been pumped to transparency at the cavity resonance wavelength.Comment: 10 pages, 7 figure

Solar steam generation by heat localization

Currently, steam generation using solar energy is based on heating bulk liquid to high temperatures. This approach requires either costly high optical concentrations leading to heat loss by the hot bulk liquid and heated surfaces or vacuum. New solar receiver concepts such as porous volumetric receivers or nanofluids have been proposed to decrease these losses. Here we report development of an approach and corresponding material structure for solar steam generation while maintaining low optical concentration and keeping the bulk liquid at low temperature with no vacuum. We achieve solar thermal efficiency up to 85% at only 10 kW m[superscript −2]. This high performance results from four structure characteristics: absorbing in the solar spectrum, thermally insulating, hydrophilic and interconnected pores. The structure concentrates thermal energy and fluid flow where needed for phase change and minimizes dissipated energy. This new structure provides a novel approach to harvesting solar energy for a broad range of phase-change applications.United States. Dept. of Energy. Office of Basic Energy Sciences (Energy Frontiers Research Center. Award DE-SC0001299)United States. Dept. of Energy. Office of Basic Energy Sciences (Energy Frontiers Research Center. Award DE-FG02-09ER46577))United States. Air Force Office of Scientific Research (FA9550-11-1-0174)Masdar Institute of Science & Technology - MIT Technology & Development ProgramNatural Sciences and Engineering Research Council of Canad

Efficient and Stable Inverted Wide-Bandgap Perovskite Solar Cells and Modules Enabled by Hybrid Evaporation-Solution Method

Wide-bandgap perovskite solar cells (WBG-PSCs), when partnered with Si bottom cells in tandem configuration, can provide efficiencies up to 44%; yet, the development of stable, efficient, and scalable WBG-PSCs is required. Here, the utility of the hybrid evaporation-solution method (HESM) is investigated to meet these demanding requirements via its unique advantages including ease of control and reproducibility. A PbI2/CsBr layer is co-evaporated followed by coating of organic-halide solutions in a green solvent. Bandgaps between 1.55–1.67 eV are systematically screened by varying CsBr and MABr content. Champion efficiencies of 21.06% and 20.35% in cells and 19.83% and 18.73% in mini-modules (16 cm2) for perovskites with 1.64 and 1.67 eV bandgaps are achieved, respectively. Additionally, 18.51%-efficient semi-transparent WBG-PSCs are implemented in 4T perovskite/bifacial silicon configuration, reaching a projected power output of 30.61 mW cm−2 based on PD IEC TS 60904-1-2 (BiFi200) protocol. Despite similar bandgaps achieved by incorporating Br via MABr solution and/or CsBr evaporation, PSCs having a perovskite layer without MABr addition show significantly higher thermal and moisture stability. This study proves scalable, high-performance, and stable WBG-PSCs are enabled by HESM, hence their use in tandems and in emerging applications such as indoor photovoltaics are now within reach.</p

Absorption bleaching by stimulated emission in erbium-doped silicon-rich silicon nitride waveguides

Stimulated emission from sensitized erbium ions in silicon-rich silicon nitride is demonstrated by pump-probe measurements carried out in waveguides. A decrease in the photoinduced absorption of the probe at the wavelength of erbium emission is observed and is attributed to stimulated emission from erbium excited indirectly via localized states in the silicon nitride matrix. (C) 2010 Optical Society of Americ

Efficient Light Trapping in Inverted Nanopyramid Thin Crystalline Silicon Membranes for Solar Cell Applications

Thin-film crystalline silicon (c-Si) solar cells with light-trapping structures can enhance light absorption within the semiconductor absorber layer and reduce material usage. Here we demonstrate that an inverted nanopyramid light-trapping scheme for c-Si thin films, fabricated at wafer scale via a low-cost wet etching process, significantly enhances absorption within the c-Si layer. A broadband enhancement in absorptance that approaches the Yablonovitch limit (Yablonovitch, E. J. Opt. Soc. Am.1987, 72, 899–907 ) is achieved with minimal angle dependence. We also show that c-Si films less than 10 μm in thickness can achieve absorptance values comparable to that of planar c-Si wafers thicker than 300 μm, amounting to an over 30-fold reduction in material usage. Furthermore the surface area increases by a factor of only 1.7, which limits surface recombination losses in comparison with other nanostructured light-trapping schemes. These structures will not only significantly curtail both the material and processing cost of solar cells but also allow the high efficiency required to enable viable c-Si thin-film solar cells in the future.United States. Dept. of Energy (Sunshot Project Award DEEE0005320)National Science Foundation (U.S.) (Nanoscale Science and Engineering Initiative Award CMMI-0751621)Massachusetts Institute of Technology. Laboratory for Energy and the Environmen

In‐Depth Compositional Analysis of the Carbon‐Rich Fine‐Grain Layer in Solution‐Processed CZTSSe Films Accessed by a Photonic Lift‐Off Process

Abstract The existence of a fine‐grain (FG) sub‐layer between the top large‐grain (LG) layer and the back contact is widely observed in kesterite absorbers prepared with organic solvents. In this paper, the distinguishing features of the lifted‐off carbon‐rich FG layer are investigated through direct analysis with a series of characterization techniques, including X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance, X‐ray diffraction, and scanning electron microscopy. To access the FG layer for direct probing, a scalable and repeatable photonic lift‐off method is developed for carrying out the separation of the kesterite absorber layer from the Mo‐coated glass substrate. A very high light intensity of 4 kW cm−2 for a short interval of 1 ms is optimized by COMSOL simulations, and successful implementation is demonstrated. The XPS analysis has revealed significant carbon content at the exposed FG surface, which explains the hindrance of grain growth due to carbon abundance. The variations in cations and anions concentrations from FG layer leading into LG region are explored through argon ions (Ar+) assisted XPS depth profiling. The observed significant differences between the composition of FG and LG regions are speculated to negatively impact the performance of solar cells

Strain Engineering of Germanium Nanobeams by Electrostatic Actuation

Abstract Germanium (Ge) is a promising material for the development of a light source compatible with the silicon microfabrication technology, even though it is an indirect-bandgap material in its bulk form. Among various techniques suggested to boost the light emission efficiency of Ge, the strain induction is capable of providing the wavelength tunability if the strain is applied via an external force. Here, we introduce a method to control the amount of the axial strain, and therefore the emission wavelength, on a suspended Ge nanobeam by an applied voltage. We demonstrate, based on mechanical and electrical simulations, that axial strains over 4% can be achieved without experiencing any mechanical and/or electrical failure. We also show that the non-uniform strain distribution on the Ge nanobeam as a result of the applied voltage enhances light emission over 6 folds as compared to a Ge nanobeam with a uniform strain distribution. We anticipate that electrostatic actuation of Ge nanobeams provides a suitable platform for the realization of the on-chip tunable-wavelength infrared light sources that can be monolithically integrated on Si chips

Correction: Engineering spin and antiferromagnetic resonances to realize an efficient direction-multiplexed visible meta-hologram

Correction for ‘Engineering spin and antiferromagnetic resonances to realize an efficient direction-multiplexed visible meta-hologram’ by Muhammad Afnan Ansari et al., Nanoscale Horiz., 2020, 5, 57–64. The authors regret that a funding source was omitted in the ‘Acknowledgements’ section of the original article. A revised version of the ‘Acknowledgements’ section, adding the funding received from the National Research Foundation of Korea under grant number NRF-2019R1A5A8080290, is provided below. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.11Ysciescopu