•Living creatures use micro- and nano-scale structures to manipulate light (e.g., for antireflection, maximal reflection, iridescent coloration, and efficient photosynthesis).•Optical simulations can ...help explore the frontier of micro- and nano-scale biodiversity, gain insights into colorful signals and sexual selection, identify evolutionary innovations across environments, and guide the design of new technologies inspired by natural structures.•The finite-difference time-domain (FDTD) method is a powerful numerical modeling technique to study how light interacts with materials, allowing researchers to obtain reflection, transmission, diffraction, absorption, and more.•FDTD is a good choice of method for researchers who wish to simulate a naturalistic broadband light source, study complicated structures that cannot easily be analyzed through analytical optical theory alone, conduct parameter sweeps over structures of interest, and test potential bio-inspired applications.•FDTD is often used in conjunction with experimental techniques to probe how organisms’ structures produce a variety of optical effects, and the workflow is accessible to researchers from many different backgrounds.
Light influences most ecosystems on earth, from sun-dappled forests to bioluminescent creatures in the ocean deep. Biologists have long studied nano- and micro-scale organismal adaptations to manipulate light using ever-more sophisticated microscopy, spectroscopy, and other analytical equipment. In combination with experimental tools, simulations of light interacting with objects can help researchers determine the impact of observed structures and explore how variations affect optical function. In particular, the finite-difference time-domain (FDTD) method is widely used throughout the nanophotonics community to efficiently simulate light interacting with a variety of materials and optical devices. More recently, FDTD has been used to characterize optical adaptations in nature, such as camouflage in fish and other organisms, colors in sexually-selected birds and spiders, and photosynthetic efficiency in plants. FDTD is also common in bioengineering, as the design of biologically-inspired engineered structures can be guided and optimized through FDTD simulations. Parameter sweeps are a particularly useful application of FDTD, which allows researchers to explore a range of variables and modifications in natural and synthetic systems (e.g., to investigate the optical effects of changing the sizes, shape, or refractive indices of a structure). Here, we review the use of FDTD simulations in biology and present a brief methods primer tailored for life scientists, with a focus on the commercially available software Lumerical FDTD. We give special attention to whether FDTD is the right tool to use, how experimental techniques are used to acquire and import the structures of interest, and how their optical properties such as refractive index and absorption are obtained. This primer is intended to help researchers understand FDTD, implement the method to model optical effects, and learn about the benefits and limitations of this tool. Altogether, FDTD is well-suited to (i) characterize optical adaptations and (ii) provide mechanistic explanations; by doing so, it helps (iii) make conclusions about evolutionary theory and (iv) inspire new technologies based on natural structures.
A novel Mo/ZrSiN/ZrSiON/SiO2 solar selective absorbing coating has been investigated, which was prepared by magnetron sputtering on stainless steel substrate. A high solar absorptance of 0.94 and a ...low thermal emittance of 0.06 at 25°C were achieved. By proportionally decreasing the thicknesses of the ZrSiN, ZrSiON and SiO2 layers, the thermal emittance at 500°C was decreased significantly from 0.19 to 0.12 (Δε=0.07) while keeping the solar absorptance unchanged. The coating also showed high thermal stability at 500°C in vacuum, implying that it is a promising candidate for high temperature concentrated solar power (CSP) applications.
•A novel Mo/ZrSiN/ZrSiON/SiO2 coating was simulated and prepared.•Absorptance of 0.94 and emittance (500°C) of 0.12 were obtained.•The coating is thermally stable up to 500°C for 500h in vacuum.
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•A compound parabolic concentrator enhanced radiative cooling (CPC-RC) is studied.•CPC can facilitate directional concentration of emitted thermal radiation in RC.•CPC can also help ...to shield the adverse incoming radiation in RC.•The performance of the CPC-RC module is 30% higher than that of a flat-RC module.•The CPC-RC can reduce the requirement on the emitter property for the daytime RC.
Radiative sky cooling (RC) is a promising solution for meeting the growing cooling demands by passively dissipating waste heat into frigid outer space. However, current RC systems suffer from low cooling power density and limited installation flexibility, impeding their effective application as building cooling strategies. To overcome these challenges, a novel concentrated RC system coupled with a compound parabolic concentrator (CPC) is proposed and experimentally studied. The objective is to investigate the effectiveness of the CPC in enhancing the cooling capability of the RC system and the feasibility of achieving all-day RC in unfavorable working conditions when integrated with building roofs. During nighttime experiments in the humid Nottingham region, the CPC-RC system exhibited an average emitter temperature that was 5.83 °C lower than the ambient temperature, representing a 30 % and 13.6 % improvement in RC performance compared to the flat-RC system and trapezoidal-concentrated RC system, respectively. The Photopia optical software simulation indicates that when the modules are tilted to the north, the CPC functions as a solar shield, effectively limiting solar radiation reaching the emitter surface, which is advantageous for conducting daytime RC experiments. In the daytime experiment, the emitter temperature of the CPC-RC module in anti-sunward group was still 1.59 °C lower than the ambient temperature and 5.49 °C lower than that of flat-RC module. At night, the CPC-RC module of the three placement groups all showed the highest RC effect in the same group. The average emitter temperature of the CPC-RC module in the horizontal placement group is 0.6 °C lower than that of the flat RC module. This novel CPC-RC scheme presents a new energy-saving strategy for buildings and showcases its potential for achieving 24-hour RC when integrated into anti-sunward roofs.
A high-performance monolithic perovskite/organic tandem solar cell based on the integration of a large bandgap CsPbI2Br inorganic perovskite front cell with a narrow bandgap PM6:Y6-based or ...PTB7-Th:O6T-4F-based bulk-heterojunction organic rear cell is demonstrated. Large bandgap inorganic perovskites are well suited candidates for the front cell due to their excellent optoelectronic properties and broad absorption for visible light, they also possess smaller voltage loss (Eloss) and higher external quantum efficiency (EQE) response when compare to their organic counterparts with approximate bandgap. Low bandgap organic solar cells offer potentially better stability and absorption tunability compared with the Sn-based perovskite counterparts, making them be good candidates for the rear cell of the tandem cells. As a result, the best power conversion efficiency (PCE) of the perovskite/organic tandem cell presented in this work reaches over 18%. In addition, based on the photovoltaic performance parameters (EQE, fill factor (FF), Eloss) that have already been achieved in state-of-the-art organic and perovskite solar cells, we further evaluate the potential PCE of the perovskite/organic tandem cells, showing a maximum calculated PCE of over 31% when the bandgaps of the subcells are optimized. This work paves the way for the development of hybrid tandem solar cells with promising performance.
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•A high-performance perovskite/organic monolithic tandem solar cell with power conversion efficiency over 18% is demonstrated.•This type of tandem cell can be potentially produced by all-solution process to realize low cost and high-performance devices.•Semi-empirical analysis suggests that potential PCE of over 31% can be achieved by the perovskite/organic tandem cell.
The article commences with a review focusing on three critical aspects of the perovskite/Si tandem technology: the evolution of efficiencies to date, comparisons of Si subcell choices, and the ...interconnection design strategies. Building on this review, a clear route is provided for minimizing optical losses aided by optical simulations of a recently reported high‐efficiency perovskite/Si tandem system, optimizations which result in tandem current densities of ≈20 mAcm−2 with front‐side texture. The primary focus is on electrical modeling on the Si‐subcell, in order to understand the efficiency potential of this cell under filtered light in a tandem configuration. The possibility of increasing the Si subcell efficiency by 1% absolute is offered through joint improvements to the bulk lifetime, which exceeds 4 ms, and improves surface passivation quality to saturation current densities below 10 fA cm−2. Polycrystalline‐Si/SiOx passivating contacts are proposed as a promising alternative to partial‐area rear contacts, with the potential for further simplifying cell fabrication and improving device performance. A combination of optical modeling of the complete tandem structure alongside electrical modeling of the Si‐subcell, both with state‐of‐the‐art modeling tools, provides the first complete picture of the practical efficiency potential of perovskite/Si tandems.
Perovskite/Si tandem solar cells offer a feasible and promising approach to further reduce solar electricity costs by promising higher efficiency than their single‐junction counterparts. Prospects for achieving over 30% efficient monolithic perovskite/Si tandems in the near term using a combination of literature review with original results from numerical optoelectronic simulations are presented in this progress report.
Many research groups work on overcoming the 30% power conversion efficiency (PCE) level for perovskite/silicon tandem solar cells with various approaches. The most common tandem architectures employ ...a transparent conductive oxide (TCO) front electrode. Due to its fast deposition and up-scalability, sputter deposition is the preferred method for TCO deposition. The sensitive layers of perovskite solar cells are protected from sputter damage by a thermal atomic layer (ALD) deposited tin oxide (SnO2) buffer layer, which induces parasitic absorption. Here, we propose a method to reveal the impact of sputter damage on SnO2 buffer layer-free devices. By performing light intensity-dependent current density-voltage (J-V) measurements and thereby reconstructing the single-junction solar cell pseudo J-V characteristics, we could associate sputter damage with trap-assisted non-radiative recombination losses. Additionally, we demonstrate a simple method to minimize sputter damage to the perovskite solar cell to the point where a protective SnO2 buffer layer is no longer required. By lowering the sputter power density during the TCO deposition, we regained ∼13 mV open-circuit voltage and ∼3% fill factor of the devices, improving the efficiency from 13.55 to 14.17%. We show that these improvements are linked to a reduction of transport and non-radiative recombination losses. Finally, we fabricated optically superior and sputter damage-free monolithic perovskite/silicon tandem devices without needing a protective SnO2 buffer layer. By doing so, we increased the tandem device current density by 0.52 mA/cm2, representing a crucial step toward further optimizing the optical performance of tandem devices.
•In perovskite solar cells sputter damage leads to non-radiative recombination losses.•Sputter damage-induced losses are quantified by light intensity-dependent analysis.•The effect of sputter damage can be reduced by reducing the sputter power.•Tin oxide buffer layer-free tandem devices are optically superior.
•Processing defects of multi-focus cutting of transparent materials is disclosed.•Spherical aberration is concluded the main factor limiting the cutting thickness.•The aberration is dependent on the ...refractivity and the effective numerical aperture.•The aberration is compensated by redistributing multiple foci to cut 2-mm sapphire.
Laser multi-focus separation technology is an effective way to cut thick, transparent and hard materials. In this paper, factors affecting the quality of multi-focus cutting sapphire were investigated. Optical simulations analysis was performed based on experimental results to analyze multi-focal laser beam propagation from air into sapphire. The results show that the focus interval is linearly dependent on refractive index. Spherical aberration due to refractive-index mismatch disperses the laser foci, leading to a reduction in laser power density which has a significant influence on the cutting quality. The aberration is strongly dependent on the refractivity of the material and the effective numerical aperture (NA). By redesigning the distribution of multiple foci to correct spherical aberration, sapphire with a thickness of 2 mm was cut successfully at a scanning speed of 4 mm/s. The roughness of the cutting section was ∼2.5 μm, without obvious observed micro-cracks.
•A method for the optimization of the geometry of a Fresnel collector is presented.•Nonuniformly spaced mirrors with variable size and variable focal are considered.•Different optimization levels are ...presented and compared.•Cost optimization shows a gain of almost 5% w.r.t. a simple uniform optimization.•Application of the method to real systems is discussed.
Methods and results concerning the optical optimization of a linear Fresnel collector are presented. The variables considered in the optimization are the positions, widths and focal lengths of the mirrors; the mirrors can be of variable size and focal length, and they can be nonuniformly spaced. The target function to be optimized is the plant cost divided by the collected solar radiation in a year. The computation of the collected radiation and of its average on the year, and the optimization of the cost/radiation function are carried out via suitable mathematical methods and the choice of a plausible cost function. Four different levels of optimization (uniformly spaced identical mirrors; nonuniformly spaced identical mirrors; mirrors of the same width with uniform spacing and variable focal lengths; and finally a full optimization) are presented, with a discussion of the resulting gain on the target function (i.e. the reduction of the ratio between the plant cost and the collected radiation). The results show that the application of suitable optimization strategies can lead to an estimated gain around 12% with respect to the initial configuration (all mirrors identical and adjacent), and that a full optimization leads to a gain of 4.5% over a simple uniform optimization. This gain is due in large part to the possibility of regulating the focal lengths (the optimization of focals leads to a 2.8% gain over the uniform case), while only a minor improvement (less than 0.4%) is obtained with nonuniformly spaced identical mirrors.
An organic light‐emitting diode (OLED) with the blue emitter CC2TA showing thermally activated delayed fluorescence (TADF) is presented exhibiting an external quantum efficiency (ηEQE) of 11% ± 1%, ...which clearly exceeds the classical limit for fluorescent OLEDs. The analysis of the emission layer by angular dependent photoluminescence (PL) measurements shows a very high degree of 92% horizontally oriented transition dipole moments. Excited states lifetime measurements of the prompt fluorescent component under PL excitation yield a radiative quantum efficiency of 55% of the emitting species. Thus, the radiative exciton fraction has to be significantly higher than 25% due to TADF. Performing a simulation based efficiency analysis for the OLED under investigation allows for a quantification of individual contributions to the efficiency increase originating from horizontal emitter orientation and TADF. Remarkably, the strong horizontal emitter orientation leads to a light‐outcoupling efficiency of more than 30%.
The thermally activated delayed fluorescence (TADF) emitter CC2TA shows a high degree of horizontal orientation. Using excited states lifetime measurements of the prompt fluorescence, its radiative quantum efficiency can be determined. This is the basis for a comprehensive analysis of the efficiency boost of organic light‐emitting diodes beyond the classical limit due to emitter orientation and TADF.
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