Recently, many research efforts have been dedicated to improving light coupling into solar cells and reducing optical losses. Promising candidates regarding scalability include direct nano-structuring of the absorber layer, anti-reflective (AR) coatings, or combining both, e.g., pyramidal textures with a conformal coating. However, many of these methods are either insufficient or infeasible for application in thin solar cells. Moreover, approaches based on directly texturing the silicon interface simultaneously strongly increase surface recombination, thus degrading the electronic properties of the solar cell. To circumvent these issues, conformal graded-index metasurfaces with a correlated positional disorder for light trapping in solar cells are proposed and experimentally demonstrated in this contribution. When considered as a part of a prototypical solar cell geometry, a broadband reduction in reflection is observed that results in photocurrent enhancement. The combined consideration of disorder and conformal graded-index layers outperforms structures containing only one of these components. The computational guidance toward optimized designs promises to adjust the framework to other settings. The possibility for large-scale fabrication of the samples paves the way toward a future generation of supporting photonic structures in solar cells. This work demonstrates the use of gradient-index metasurface with correlated disorder for light management in solar cells. Such a metasurface is created via self-assembly nanofabrication and atomic layer deposition techniques on macroscopically large wafers. The results unequivocally demonstrate the significant improvement in light trapping and anti-reflective performance for a standard solar cell compared to bare nanostructures and a linear gradient anti-reflection coating. image

A major loss mechanism in organic light emitting diodes (OLEDs) is the coupling of the emitter molecule light field to waveguide modes in the OLED thin film stack. In this work, a disordered 2D array of TiO2 nanodisk scatterers is integrated into the OLED substrate to enable efficient light extraction from these waveguide modes. Fabrication of the nanodisks is based on a bottom‐up, colloidal lithography technique and subsequent pattern transfer into high refractive index TiO2 via reactive ion etching. The substrates are completed by spin‐coating a polymer planarization layer before applying the OLED thin film stack. This ensures reproducible optoelectronic properties of the OLED through leaving the electrically active layers planar. Simultaneously, the nanodisks in close vicinity to the thin film stack ensure efficient out‐of‐plane scattering of waveguide modes. In a monochromatic OLED (center wavelength λ0 = 520 nm), a 44.2%rel increase in external quantum efficiency is achieved in comparison to a device without scattering structure. An in‐depth numerical analysis reveals that this significant enhancement is only partly due to the out‐coupling of waveguide modes. Additional enhancement is suspected to result from out‐coupling of substrate modes through scattering by the nanodisks. Further improvements to the scattering structure are numerically evaluated.

While hyperuniform‐disordered patterns have been researched from a theoretical perspective for two decades, large scale experimental realizations remain scarce. In this work, as a potential route to overcome this issue, 2D patterns are evaluated that form through sedimentation of charged particles from a colloidal dispersion at an electrically conductive substrate. The particles are given a sufficient amount of time to form various morphologies and then locked in place irreversibly by setting attractive particle‐substrate potentials. The system can be interpreted as a 2D, however, comparisons to previous numerical works remain qualitative, as the latter do not consider the constant exchange of particles with the 3D bulk of the dispersion. For monodisperse colloids, depending on particle density, random sequential adsorption‐like, fluid, and crystalline phases are obtained, of which the fluid phase most effectively suppresses density fluctuations, or in terms of the hyperuniformity metric H S ≈ 8.7 × 10 −3 . For bidisperse colloids, the particle sizes tend to segregate at high density thereby reducing the ability of the system to suppress density fluctuations, which are explained within the framework of a eutectic system. The latter also provides hints that the degree of hyperuniformity can be increased by tuning the size distribution to the eutectic point.

High-index nanodisk metasurfaces with correlated disorder are promising as an anti-reflective metasurface for several optoelectronic devices. However, their computational analysis remains a major challenge since capturing the long-range scattering response of these disordered nanostructures requires a sufficiently large simulation domain, inhibiting simulation studies due to high computational costs. To overcome this challenge, we investigate the collective coordinate method (CCM) to identify smaller and optimal super-cells feasible for computational analysis that still represent the spatial correlation characteristics of the larger system. Our focus lies in determining the reliability of the optical response obtained from such optimized samples compared to ensemble-averaged unoptimized samples and large-scale samples that include long-range information. Our results in the context of solar cells indicate that CCM offers a robust solution across all scatterer parameters and domain sizes to accurately simulate the response of a large-scale system with hyperuniform disorder. Our work unlocks a use of such a reciprocal-space optimization scheme to reliably simulate metasurfaces with tailored disorder.

A large variety of different strategies has been proposed as alternatives to random textures to improve light coupling into solar cells. While the understanding of dedicated nanophotonic systems deepens continuously, only a few of the proposed designs are industrially accepted due to a lack of scalability. In this Article, a tailored disordered arrangement of high-index dielectric submicron-sized titanium dioxide (TiO2) disks is experimentally exploited as an antireflective Huygens' metasurface for standard heterojunction silicon solar cells. The disordered array is fabricated using a scalable bottom-up technique based on colloidal self-assembly that is applicable virtually irrespective of material or surface morphology of the device. We observe a broadband reduction of reflectance resulting in a relative improvement of a short-circuit current by 5.1% compared to a reference cell with an optimized flat antireflective indium tin oxide (ITO) layer. A theoretical model based on Born's first approximation is proposed that links the current increase in the arrangement of disks expressed in terms of the structure factor S(q) of the disk array. Additionally, we discuss the optical performance of the metasurface within the framework of helicity preservation, which can be achieved at specific wavelengths for an isolated disk for illumination along the symmetry axis by tuning its dimensions. By comparison to a simulated periodic metasurface, we show that this framework is applicable in the case of the structure factor approaching zero and the disks' arrangement becoming stealthy hyperuniform.

A broadband nanodisk-based anti-reflection coating is experimentally shown to increase the short circuit current of industrial type solar cells with several square centimeter area by 5.1 % compared to an optimized flat coating.

Arrays of nanoparticles exploited in light scattering applications commonly only feature either a periodic or a rather random arrangement of its constituents. For the periodic case, light scattering is mostly governed by the strong spatial correlations of the arrangement, expressed by the structure factor. For the random case, structural correlations cancel each other out and light scattering is mostly governed by the scattering properties of the individual scatterer, expressed by the form factor. In contrast to these extreme cases, it is shown here that hyperuniform disorder in self-organized large-area arrays of high refractive index nanodisks enables both structure and form factor to impact the resulting scattering pattern, offering novel means to tailor light scattering. The scattering response from the authors' nearly hyperuniform interfaces can be exploited in a large variety of applications and constitutes a novel class of advanced optical materials.

Light management in photovoltaics continues to be an important ingredient when working towards high efficiency devices. Various approaches have been perceived. Besides spectral modification, e.g. based on up- or down-conversion, the spatial and angular redistribution of light is important. For the latter aspect, on which we concentrate here, various supporting photonic structures were suggested, e.g. photonic crystals, metallic nanostructures, or textured interfaces. From a higher executive perspective we can categorize most structures as being either periodic or random. The emergence of such material classes is explained by the fabrication means. The Fourier spectrum, i.e. the angular distribution with which photonic modes can be excited from such structures beyond specific near-field effects is either discrete and wavelength sensitive or unspecific and spectrally flat. Both combinations are far from optimum when integrating them into photovoltaic devices.

A method is presented to fabricate large-scale 2D colloidal patterns of correlated disorder for photonic applications. Easy-to-access parameters allow to tune the structure factor and thus tailor light scattering of the disordered structures on demand.

The availability of optimum textures for the purpose of light trapping in solar cells is at stake. Here, we discuss how they can be obtained with a large-area scalable bottom-up approach that utilizes as a template monolayers of densely packed nanospheres from a colloidal solution with tailored size distribution. Theoretically, we show that the surface textures' geometry can be predicted and tuned from a colloidal solution with given nanosphere sizes and relative occurrence probability. With only simple monolayers comprised of two nanosphere size species, we show that one can already obtain a useful scattering pattern relevant for rear scattering light trapping textures. We proceeded to study the application of such textures in thin-film crystalline silicon (c-Si) solar cells. Such monolayers can be tuned to provide diffraction patterns, which form an annulus in Fourier space such that stronger scattering occurs at oblique angles. For such two species nanosphere monolayers, the nanosphere sizes dominantly influence the diffraction efficiency and minimum and maximum scattering angles. The relative occurrence probability of each nanopshere species influences the amount of diffraction states accessible, which translates to how broad the annulus region in Fourier space can be. The simplicity of the monolayer and the behavior of the scattering response allows to easily estimate nanosphere size ranges of interest by considering the radiation condition in c-Si and in air. In optimizing the monolayer parameters to obtain optimum rear scattering light trapping textures, we inspect approaches that avoid the severe computational costs, which typically follow the modeling of random scattering geometries. In particular, we investigate the applicability of utilizing the surface texture's Power Spectral Density (PSD) and alternatively rigorous diffraction calculations in a semi-infinite c-Si superstrate to deduce net short-circuit current enhancement dependence on the monolayer parameters. The widely used PSD based prediction is shown to significantly deviate in important parameter ranges, where an optimal response can be obtained. This is related to the limitation of the PSD to be used as a predictor for the scattering response at textures with a notable height modulation. In the regime where the PSD fails to be predictive, an excellent prediction on the short-circuit current enhancement can be obtained with minimal computational costs by only examining the diffraction efficiencies in a selected wavelength range where light trapping has its largest impact. We show that the integrated diffraction in the directions of interest at the wavelength of 700 nm is sufficiently representative for the considered 1 μm thin-film c-Si cell and light trapping scheme. Fullwave simulations reveal that the integrated diffraction at 700 nm and the short-circuit current have coinciding trends in their dependency on the nanosphere size distribution. We furthermore explore the usage of the nanosphere monolayer template to obtain front surface textures, which provide mainly anti-reflection properties. This is done by considering an inverse pattern of the template to make use of the needle-like structures that emerge from the inverted nanosphere monolayer. The conditions needed for the monolayer parameters in order to ensure broadband suppression of reflection are discussed.

We study the light-trapping properties of surface textures generated by a bottom-up approach, which utilizes monolayers of densely deposited nanospheres as a template. We demonstrate that just allowing placement disorder in monolayers from identical nanospheres can already lead to a significant boost in light-trapping capabilities. Further absorption enhancement can be obtained by involving an additional nanosphere size species. We show that the Power Spectral Density provides limited correspondence to the diffraction pattern and in turn to the short-circuit current density enhancement for large texture modulations. However, in predicting the optimal nanosphere size distribution, we demonstrate that full-wave simulations of just a c-Si semi-infinite halfspace at a single wavelength in the range where light trapping is of main importance is sufficient to provide an excellent estimate. The envisioned bottom-up approach can thus reliably provide good light-trapping surface textures even with simple nanosphere monolayer templates defined by a limited number of control parameters: two nanosphere radii and their occurrence probability.

Mie resonances of high-refractive index nanostructures provide strong and spectrally broadband scattering. In this numerical work, we investigate the feasibility of amourphous silicon nanodisks at the planar rear side of crystalline silicon solar cells for light trapping.

In the efforts to enhance absorption in thin film solar cells, a plethora of scattering surface textures for enhancing light incoupling and light trapping has been explored. One consistent finding in many different studies is the fact that employing disorder can be beneficial by virtue of inducing a more broadband response. However, not all disordered structures are equivalent. Disorder may also enhance light scattering within the escape cone, which in turn result in less absorption. Obtaining the most out of introducing disorder therefore requires care, a challenge also encountered in other applications. Even more troubling, optimizing disordered light scattering textures is a major design challenge, especially due to the requirement to consider an extended spatial domain when modelling them. Here, we give an overview of our efforts in tackling these challenges. We present a semi-analytical perturbative method based on Green's function for cost efficient forward and inverse modelling of quasi-periodic and disordered surface textures. Our formalism side-steps typical shallow amplitude limitations by appropriate choice of the reference structure. We further present a bottom-up self assembled fabrication method for disordered interfaces, which allow indirect tuning of the scattering properties by controlling the building blocks' geometrical parameters.

Highly efficient anti‐reflection textures for solar cells that allow a fabrication using a two‐step bottom‐up approach are reported. Hereby, nanospheres of tailored sizes are deposited as a monolayer on a substrate and the resulting height profile is used as a template for structuring the silicon surface. By applying these textures to crystalline silicon solar cells, it is numerically shown that such interfaces provide excellent broadband suppression of reflection while also enhancing the effective path‐length through oblique‐angle scattering into the medium. Reflectance values around 5% can be reached and sustained for incident angles up to 40°. The short‐circuit current density obtained with the disordered texture and assuming two‐pass absorption in 10 µm thick crystalline silicon reaches 25.3 mA cm−2, which is close to the corresponding value achievable with a Lambertian texture (27.9 mA cm−2). Considering the simplicity and low cost of the approach, these textures may serve as a promising alternative to other often used anti‐reflection textures, especially for large‐scale devices.

We exploit two dimensional arrangements of nanoparticles that serve as templates to fabricate substrates for light-management in optoelectronic devices. Strategies to tailor substrate topographies through self-organization of particles are described.

Reactive atmospheric plasma jets containing halogenous compounds are employed as locally acting tools for surface figure shaping or surface modification in ultra-precision surface machining technologies. In the current study, the interaction between an atmospheric CCl4/O-2 containing plasma jet with silicon surface is investigated aiming at elucidating the chemical kinetics of surface reactions. Different process regimes are identified comprising material removal as well as polymeric and oxide layer formation, which depend on the ratio of the reactive components and substrate surface temperature. XPS and SEM measurements support the findings.

We numerically explore a bottom-up approach using a monolayer of nanospheres to define an optimum surface texture for light trapping. The impact of nanosphere size distributions on the defined surface’s scattering response is studied.

Photonic crystals provide new concepts for light management. Here, we fabricate 3DPCs via spray coating, which is a fast, cheap, and scalable technique, and apply them as backside structures in solar cells and solar modules.