Tom Veeken

Control over the concentration of light is of great importance for many optical systems. Light-emitting diodes (LEDs), lasers, and optical amplifiers necessitate control over the emission of light inside and out of the system. Optical sensors, detectors, and photovoltaic systems typically benefit from light trapping. To achieve enhanced light trapping in an optical waveguide, we demonstrate anisotropic luminophore emission in a luminescent solar concentrator (LSC) waveguide geometry. By embedding CdSe-CdZnS nanoplatelet emitters into high-index TiO2 nanocylinders, we alter their angular emission profile to increase emission into total internal reflection (TIR) angles. The emission direction can be controlled by optimizing Mie-like multipolar resonances in the individual nanocylinders and the interaction with the lattice. Angle-resolved photoluminescence measurements on the fabricated nanocylinder arrays corroborate this understanding. By optimizing the cylinder shape and lattice spacing, we show an increase in emission into TIR angles from 75% (isotropic emission) to 83.5%. This novel approach to the integration of nanoscale photonic structures and emitters paves the way for enhanced emission control in photovoltaic systems, as well as in solid-state lighting and smart displays.

We present an effective process sequence for the deposition of indium nanostructures using molecular beam epitaxy (MBE) on a silicon substrate. Using a template structure composed of inverted pyramids and V-grooves, we deposit indium nanostructures with various dimensions. Spatially resolved cathodoluminescence spectroscopy (CL) using an electron-beam energy of 30 keV electrons shows a localized surface plasmon (LSP) resonance in spherical particles with a peak wavelength at 300 nm and a full width at half-maximum of 70 nm for the smallest particles (diameter of 85 nm), showing high optical quality of the grown indium. V-groove template structures create indium nanowires for which CL spectroscopy reveals efficient propagation of surface plasmon polaritons (SPPs), and angle-resolved CL on the periodic inverted pyramids reveals optical lattice resonances arising from the array’s periodicity. The high optical quality of these nanostructures enables further applications of plasmonic nanostructures in the ultraviolet (UV) spectral range.

Two‐terminal fully textured perovskite silicon tandem solar cells have recently advanced significantly and are quickly moving toward scalable production. While µm‐sized texturing of the silicon solar cell enables minimizing reflection losses, and tuning of the perovskite layer thickness allows optimizing the photo‐generated current distribution between subcells, both approaches introduce challenges at the development stage. One of these challenges is the accurate optoelectronic assessment of perovskite films with photoluminescence (PL) spectroscopy. In this work, we study effects of optical self‐absorption on the PL of perovskite films conformally coated on industry‐compatible textured silicon with pyramid heights ranging from 6 µm. Our findings indicate that with increasing pyramid height, the PL peak energy shows a blueshift of 20–30 meV. Similarly, increasing the perovskite thickness on a fixed texture pattern induces a redshift. Three‐dimensional confocal laser scanning PL microscopy, combined with statistical ray optical simulations, reveals that photon reabsorption in the perovskite film plays an important role in the texture‐dependent and thickness‐dependent PL responses. This optical effect, besides previously reported changes in perovskite mechanical properties due to silicon texture, is crucial to consider for accurate assessment of PL, and for efficient optimization of perovskite silicon tandems with advanced optical designs.

Passive radiative cooling is a method to dissipate excess heat from a material by the spontaneous emission of infrared thermal radiation. For a solar cell, the challenge is to enhance PRC while retaining transparency for sunlight above the bandgap. Here, we design a hexagonal array of cylinders etched into the top surface of silica solar module glass to enhance passive radiative cooling. Multipolar Mie-like resonances in the cylinders are shown to cause antireflection effects in the infrared, which results in enhanced infrared emissivity. Using Fourier transform infrared spectrometry we measure the hemispherical reflectance of the fabricated structures and find the emissivity of the silica cylinder array in good correspondence with the simulated results. The microcylinder array increases the average emissivity between λ = 7.5-16 μm from 84.3% to 97.7%, without reducing visible light transmission.

Black silicon (BSi) is a branch of silicon material whose surface is specially processed to a micro/nanoscale structure, which can achieve ultra‐low reflectance or ultra‐high electrochemical reactivity. The diversity and complex surface structures of BSi make it challenging to commercialize BSi devices. Modeling and simulation are commonly used in the semiconductor industry to help in better understanding the material properties, predict the device performance, and provide guidelines for fabrication parameters’ optimization. The biggest challenge for BSi device modeling and simulation is obtaining accurate input surface morphological data. In this work, the 3D models of challenging BSi textures are compared as obtained by atomic force microscopy (AFM) and plasma focused ion beam (PFIB) tomography techniques. In previous work, the PFIB tomography workflow toward the application of surface topography is optimized. In this work, the 3D models obtained from both AFM and PFIB are comprehensively compared, by using the surface models as inputs for finite‐difference time‐domain‐based optical simulation. The results provide strong evidence that PFIB tomography is a better choice for characterizing highly roughened surface such as BSi and provides surface 3D models with better reliability and consistency.

We present a soft-stamping method to selectively print a homogenous layer of CdSeTe/ZnS core–shell quantum dots (QDs) on top of Si nanocylinders with Mie-type resonant modes. Depending on the cylinder shape, we direct the QD emission up or down.

The emergence of nanotextures in photovoltaics has resulted in challenges associated with optical modelling. Whilst rigorous methods exist to accurately solve these textures, the computational effort required limits the scope of modeling applications. The effective medium approximation (EMA) is a potential alternative to provide rapid modeling results which can be easily integrated with ray tracing of large complex structures. However, the validity of this technique is strongly dependent on the size of features relative to the wavelength of interest, making the application of EMA ambiguous for many situations. This paper aims to address this issue by comparing the simulated results between EMA and finite element methods for three randomly distributed silicon textures with and without a dielectric layer. Criteria for which the EMA approach is valid are proposed and generalized using ratios between root-mean-square roughness, correlation length and incident wavelength, making these limits broadly applicable, beyond that of just the nanotexture under specific solar spectrum regimes. The results in this work apply to random, isotropic textures under normally incident light. Based on the proposed criteria, the validity of different optical simulation techniques for a set of industrial photovoltaic textures is discussed. This analysis reveals a region within which neither geometric optics nor EMA are adequate for calculating the reflectivity of a textured surface, and hence FDTD or other new approaches are required.