Comparing methods to deposit Pd-In catalysts on hydrogen-permeable hollow-fiber membranes for nitrate reduction.

Catalytic hydrogenation of nitrate in water has been studied primarily using nanoparticle slurries with constant hydrogen-gas (H) bubbling. Such slurry reactors are impractical in full-scale water treatment applications because 1) unattached catalysts are difficult to be recycled/reused and 2) gas bubbling is inefficient for delivering H. Membrane Catalyst-film Reactors (MCfR) resolve these limitations by depositing nanocatalysts on the exterior of gas-permeable hollow-fiber membranes that deliver H directly to the catalyst-film.

Bifacial all-perovskite tandem solar cells.

The efficiency of all-perovskite tandem devices falls far below theoretical efficiency limits, mainly because a widening bandgap fails to increase open-circuit voltage. We report on a bifacial all-perovskite tandem structures with an equivalent efficiency of 29.3% under back-to-front irradiance ratio of 30.

Amorphous silicon carbide high contrast gratings as highly efficient spectrally selective visible reflectors.

We report spectrally selective visible wavelength reflectors using hydrogenated amorphous silicon carbide (a-SiC:H) as a high index contrast material. Beyond 610nm and through the near infrared spectrum, a-SiC:H exhibits very low loss and exhibits an wavelength averaged index of refraction of n = 3.1.

Resolving spatial and energetic distributions of trap states in metal halide perovskite solar cells.

We report the profiling of spatial and energetic distributions of trap states in metal halide perovskite single-crystalline and polycrystalline solar cells. The trap densities in single crystals varied by five orders of magnitude, with a lowest value of 2 × 10 per cubic centimeter and most of the deep traps located at crystal surfaces. The charge trap densities of all depths of the interfaces of the polycrystalline films were one to two orders of magnitude greater than that of the film interior, and the trap density at the film interior was still two to three orders of magnitude greater than that in high-quality single crystals.

Triple-halide wide-band gap perovskites with suppressed phase segregation for efficient tandems.

Wide-band gap metal halide perovskites are promising semiconductors to pair with silicon in tandem solar cells to pursue the goal of achieving power conversion efficiency (PCE) greater than 30% at low cost. However, wide-band gap perovskite solar cells have been fundamentally limited by photoinduced phase segregation and low open-circuit voltage. We report efficient 1.

Nature-inspired chiral metasurfaces for circular polarization detection and full-Stokes polarimetric measurements.

The manipulation and characterization of light polarization states are essential for many applications in quantum communication and computing, spectroscopy, bioinspired navigation, and imaging. Chiral metamaterials and metasurfaces facilitate ultracompact devices for circularly polarized light generation, manipulation, and detection. Herein, we report bioinspired chiral metasurfaces with both strong chiral optical effects and low insertion loss.

Optical modeling of wide-bandgap perovskite and perovskite/silicon tandem solar cells using complex refractive indices for arbitrary-bandgap perovskite absorbers.

Wide-bandgap perovskites are attractive top-cell materials for tandem photovoltaic applications. Comprehensive optical modeling is essential to minimize the optical losses of state-of-the-art perovskite/perovskite, perovskite/CIGS, and perovskite/silicon tandems. Such models require accurate optical constants of wide-bandgap perovskites.

Off-axis holographic lens spectrum-splitting photovoltaic system for direct and diffuse solar energy conversion.

This paper describes a high-efficiency, spectrum-splitting photovoltaic module that uses an off-axis volume holographic lens to focus and disperse incident solar illumination to a rectangular shaped high-bandgap indium gallium phosphide cell surrounded by strips of silicon cells. The holographic lens design allows efficient collection of both direct and diffuse illumination to maximize energy yield. We modeled the volume diffraction characteristics using rigorous coupled-wave analysis, and simulated system performance using nonsequential ray tracing and PV cell data from the literature.

An all-gas-phase approach for the fabrication of silicon nanocrystal light-emitting devices.

We present an all-gas-phase approach for the fabrication of nanocrystal-based light-emitting devices. In a single reactor, silicon nanocrystals are synthesized, surface-functionalized, and deposited onto substrates precoated with a transparent electrode. Devices are completed by evaporation of a top metal electrode.

Nanocrystal inks without ligands: stable colloids of bare germanium nanocrystals.

Colloidal semiconductor nanocrystals typically have ligands attached to their surfaces that afford solubility in common solvents but hinder charge transport in nanocrystal films. Here, an alternative route is explored in which bare germanium nanocrystals are solubilized by select solvents to form stable colloids without the use of ligands. A survey of candidate solvents shows that germanium nanocrystals are completely solubilized by benzonitrile, likely because of electrostatic stabilization.

Germanium and silicon nanocrystal thin-film field-effect transistors from solution.

Germanium and silicon have lagged behind more popular II-VI and IV-VI semiconductor materials in the emerging field of semiconductor nanocrystal thin film devices. We report germanium and silicon nanocrystal field-effect transistors fabricated by synthesizing nanocrystals in a plasma, transferring them into solution, and casting thin films. Germanium devices show n-type, ambipolar, or p-type behavior depending on annealing temperature with electron and hole mobilities as large as 0.

Solution-processed germanium nanocrystal thin films as materials for low-cost optical and electronic devices.

Solution-processed nanocrystal films have attracted significant interest as potential semiconductor materials with size-tunable optical and electronic properties that can be deposited with low-cost printing and coating techniques. Significant progress has been reported with groups II-VI and IV-VI nanocrystal films because the electrically insulating ligands that solubilize the nanocrystals can be easily exchanged or removed after film deposition. Although progress to date has been slow for group IV silicon and germanium nanocrystal films, this paper reports solution-processed germanium nanocrystal films with promising electrical conductivities.

Hybrid solar cells from P3HT and silicon nanocrystals.

We are reporting new hybrid solar cells based on blends of silicon nanocrystals (Si NCs) and poly-3(hexylthiophene) (P3HT) polymer in which a percolating network of the nanocrystals acts as the electron-conducting phase. The properties of composite Si NCs/P3HT devices made by spin-coating Si NCs and P3HT from a common solvent were studied as a function of Si NC size and Si NC/P3HT ratio. The open-circuit voltage and short-circuit current are observed to depend on the Si NC size due to changes in the bandgap and surface-area-to-volume ratio.