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A comprehensive algorithm for calculating the energy yield (EY) is used as the most important figure-of-merit in determining the capabilities of PV devices in realistic operation. The model is based on advanced optical modeling and extensive opto-thermo-electrical characterization. It takes the realistic environmental and device installation data fully into account, as well as the complete set of device specifications including all relevant temperature-induced variations. A detailed analysis and optimization of two-terminal perovskite-silicon tandem devices are done in terms of long-term electrical energy production at different geographical locations from distinct Köppen–Geiger–Photovoltaic climate zones (KGPV). It is shown that the optimal perovskite bandgap (E$_{G,PK}$) in a tandem device operating under realistic conditions is in all cases higher than the one optimized under STC, yet does not differ significantly from location to location, which is beneficial from the manufacturing point of view. The optimal E$_{G,PK}$ is influenced primarily by the spectral distribution of incident irradiance, and not so much by the operating temperature conditions. Moreover, a clear linear dependency between the optimal E$_{G,PK}$ and the weighted average photon energy of the incident irradiance is demonstrated, which presents an important rule for rapid tandem design.

We demonstrate a monolithic perovskite CIGS tandem solar cell with a certified power conversion efficiency PCE of 24.2 . The tandem solar cell still exhibits photocurrent mismatch between the subcells; thus optical simulations are used to determine the optimal device stack. Results reveal a high optical potential with the optimized device reaching a short circuit current density of 19.9 mA cm 2 and 32 PCE based on semiempirical material properties. To evaluate its energy yield, we first determine the CIGS temperature coefficient, which is at amp; 8722;0.38 K 1 notably higher than the one from the perovskite subcell amp; 8722;0.22 K 1 , favoring perovskite in the field operation at elevated cell temperatures. Both single junction cells, however, are significantly outperformed by the combined tandem device. The enhancement in energy output is more than 50 in the case of CIGS single junction device. The results demonstrate the high potential of perovskite CIGS tandem solar cells, for which we describe optical guidelines toward 30 PCE

A development and calibration of a detailed 3D coupled ray-wave optical model for accurate simulations of laterally varying photovoltaic structures is presented and applied for the analysis of interdigitated back contact cells. Four key aspects, which predominantly contribute to the accuracy of optical simulations are highlighted through the validation of the model. The applicability of the model is demonstrated through an example of electroluminescence simulations.

In the past decades MOS based digital integrated logic circuits have undergone a successful process of miniaturisation eventually leading to dimensions of a few nanometres. With the dimensions in the range of a few atomic radii the end of conventional MOS technology is approaching. Amongst the prospective candidates for sub 10nm logic are integrated logic circuits based on single-electron devices. In our contribution we present the use of MOSES (Monte-Carlo Single-Electronics Simulator) as a method for simulation of complementary single-electron logic circuits based on the orthodox theory. Simulations of single-electron devices including a single-electron box, a single-electron transistor and a complementary single-electron inverter were carried out. Their characteristics were evaluated at different temperatures and compared to measurement results obtained at other institutions. The potential for room-temperature operation was also assessed.

Efficient light management in monolithic perovskite/silicon tandem solar cells is one of the prerequisites for achieving high power conversion efficiencies (PCEs). Textured silicon wafers can be utilized for light management, however, this is typically not compatible with perovskite solution processing. Here, we instead employ a textured light management (LM) foil on the front-side of a tandem solar cell processed on a wafer with a planar front-side and textured back-side. This way the PCE of monolithic, 2-terminal perovskite/silicon-heterojunction tandem solar cells is significantly improved from 23.4% to 25.5%. Furthermore, we validate an advanced numerical model for our fabricated device and use it to optically optimize a number of device designs with textures at different interfaces with respect to the PCE and energy yield. These simulations predict a slightly lower optimal bandgap of the perovskite top cell in a textured device as compared to a flat one and demonstrate strong interdependency between the bandgap and the texture position in the monolithic stack. We estimate the PCE potential for the best performing both-side textured device to be 32.5% for a perovskite bandgap of 1.66 eV. Furthermore, the results show that under perpendicular illumination conditions, for optimized designs, the LM foil on top of the cell performs only slightly better than a flat anti-reflective coating. However, under diffuse illumination, the benefits of the LM foil are much greater. Finally, we calculate the energy yield for the different device designs, based on true weather data for three different locations throughout the year, taking direct as well as diffuse illumination fully into account. The results further confirm the benefits of front-side texture, even more for BIPV applications. Overall, devices built on a both-side textured silicon wafer perform best. However, we show that devices with textured LM foils on the cell's front-side are a highly efficient alternative.

Inorganic-organic perovskites like methylammonium-lead-iodide have proven to be an effective class of 17 materials for fabricating efficient solar cells. To improve their performance, light management techniques using textured surfaces, similar to those used in established solar cell technologies, should be considered. Here, we apply a light management foil created by UV nanoimprint lithography on the glass side of an inverted (p-i-n) perovskite solar cell with 16.3% efficiency. The obtained 1 mA cm(-2) increase in the short-circuit current density translates to a relative improvement in cell performance of 5%, which results in a power conversion efficiency of 17.1%. Optical 3D simulations based on experimentally obtained parameters were used to support the experimental findings. A good match between the simulated and experimental data was obtained, validating the model. Optical simulations reveal that the main improvement in device performance is due to a reduction in total reflection and that relative improvement in the short-circuit current density of up to 10% is possible for large-area devices. Therefore, our results present the potential of light management foils for improving the device performance of perovskite solar cells and pave the way for further use of optical simulations in the field of perovskite solar cells.

Hierarchical textures (combining 2D periodic large and small micro textures) as an external outcoupling solution for OLEDs have been researched, both experimentally and by optical simulations. For the case of a red bottom emitting OLED, different hierarchical textures were fabricated using laser-based methods and a replication step and applied to the OLED substrate, resulting in an increased light outcoupling. Laboratory-size OLED devices with applied textured foils show a smaller increase in efficiency compared to the final large area devices. The results show that the full exploitation of textured foils in laboratory-size samples is mainly limited by the lateral size of the thin film stack area and by limited light collection area of the measuring equipment. Modeling and simulations are used to further evaluate the full prospective of hierarchical textures in large area OLED devices. Optimization of hierarchical textures is done by simultaneously changing the aspect ratios of the small and large textures and a potential of 57% improvement in EQE compared to devices without applied textures is predicted by simulations. Optimized hierarchical textures show similar outcoupling efficiencies compared to optimized single textures, while on the other hand hierarchical textures require less pronounced features, lower aspect ratios, compared to single textures to achieve the same efficiencies. Hierarchical textures also help in eliminating flat parts that limit outcoupling efficiency. Finally, the limiting factors that prevent higher outcoupling are addressed. We show that the dominant factor is non-ideal reflection from the organic thin film stack due to parasitic absorption. In addition, possible ways to further increase the outcoupling from a thick substrate are indicated.

In ultra-thin chalcopyrite solar cells and photovoltaic modules, efficient light management is required to increase the photocurrent and to gain in conversion efficiency. In this work we employ optical modelling to investigate different optical approaches and quantify their potential improvements in the short-circuit current density of Cu(In, Ga)Se2 (CIGS) devices. For structures with an ultra-thin (500 nm) CIGS absorber, we study the improvements related to the introduction of (i) highly reflective metal back reflectors, (ii) internal nano-textures applied to the substrate and (iii) external micro-textures by using a light management foil. In the analysis we use CIGS devices in a PV module configuration, thus, solar cell structure including encapsulation and front glass. A thin Al2O3 layer was considered in the structure at the rear side of CIGS for passivation and diffusion barrier for metal reflectors. We show that not any individual aforementioned approach is sufficient to compensate for the short circuit drop related to ultra-thin absorber, but a combination of a highly reflective back contact and textures (internal or external) is needed to obtain and also exceed the short-circuit current density of a thick (1800 nm) CIGS absorber.

A variety of light management structures have been introduced in solar cells to improve light harvesting and further boost their conversion efficiency. Reliable and accurate simulation tools are required to design and optimize the individual structures and complete devices. In the first part of this paper, we analyze the performance of rigorous coupled-wave analysis (RCWA) for accurate three-dimensional optical simulation of solar cells, in particular heterojunction silicon (HJ Si) solar cells. The structure of HJ Si solar cells consists of thin and thick layers, and additionally, micro- and nano-textures are also introduced to further exploit the potential of light trapping. The RCWA was tested on the front substructure of the solar cell, including the texture, thin passivation and contact layers. Inverted pyramidal textures of different sizes were included in the simulations. The simulations rapidly converge as long as the textures are small (in the (sub)micrometer range), while for larger microscale textures (feature sizes of a few micrometers), this is not the case. Small textures were optimized to decrease the reflectance, and consequently, increase the absorption in the active layers of the solar cell. Decreasing the flat parts of the texture was shown to improve performance. For simulations of structures with microtextures, and for simulations of complete HJ Si cells, we propose a coupled modeling approach (CMA), where the RCWA is coupled with raytracing and the transfer matrix method. By means of CMA and nanotexture optimization, we show the possible benefits of nanotextures at the front interface of HJ Si solar cells, demonstrating a 13.4% improvement in the short-circuit current density with respect to the flat cell and 1.4% with respect to the cell with double-sided random micropyramids. We additionally demonstrate the ability to simulate a combination of nano- and microtextures at a single interface, although the considered structure did not show an improvement over the pyramidal textures.

We present an optical model that was developed for the purpose of simulation and optimization of luminescent down-shifting layers based on phosphor particles. The model combines three-dimensional ray tracing with a novel effective scattering approach based on the Mie scattering theory. Verification of the model with experimental results shows that the model accurately takes various layer parameters into account, such as the layer thickness, the phosphor volume concentration, and the phosphor particle size distribution. Finally, using the verified model, we investigate the concept of luminescent down-shifting in organic solar cells and discuss the optimal layer parameters. Preliminary simulation results show that in the case of the studied solar cell, an improvement in the short-circuit current density of more than 6% can be obtained.

While p-n junction solar cells have long been established as the dominant solar-cell technology in the market, the origin of the charge-carrier separation in these devices remains open to debate. It is often attributed to the built-in electric field that exists across the junction in thermodynamic equilibrium, although this interpretation can lead to physical inconsistencies. In this work we present an interpretation approach based on the analogy between a solar cell and a generalized electric source model. Our interpretation is given through a detailed analysis of the electric potential and the non-electric chemical potential across each device, which are plotted together in complete potential diagrams introduced for this purpose. We demonstrate that the driving force separating the free charge carriers in both devices originates from the change of the non-electric chemical voltage that happens once the device is brought out of thermodynamic equilibrium. This change, therefore, can be interpreted as the driving force that triggers the selective motion of charge carriers and, thus, induces the electric voltage at the terminals of the device.While p-n junction solar cells have long been established as the dominant solar-cell technology in the market, the origin of the charge-carrier separation in these devices remains open to debate. It is often attributed to the built-in electric field that exists across the junction in thermodynamic equilibrium, although this interpretation can lead to physical inconsistencies. In this work we present an interpretation approach based on the analogy between a solar cell and a generalized electric source model. Our interpretation is given through a detailed analysis of the electric potential and the non-electric chemical potential across each device, which are plotted together in complete potential diagrams introduced for this purpose. We demonstrate that the driving force separating the free charge carriers in both devices originates from the change of the non-electric chemical voltage that happens once the device is brought out of thermodynamic equilibrium. This change, therefore, can be interpreted as the ...

The perovskite / silicon-heterojunction (SHJ) tandem solar cell can theoretically overcome the efficiencies of the single junction solar cells with experimental results not far behind. Here, we use optical simulations to analyze the potential of such currently feasible monolithic perovskite / SHJ tandem devices. We consider three different device designs in the optical simulations: planar device, device built on back-side textured Si wafer, and device with textured UV Nanoimprint Lithography light management foil. For each of these three designs, the current matching point is simulated to evaluate device efficiencies. While the device with back-side textured Si wafer causes light trapping and therefore enhanced photocurrent generation for longer wavelengths, the anti-reflection foils prove to be overall more efficient as the foil significantly reduces the reflection in almost full wavelength range.

The potential of three advanced optical concepts in chalcopyrite-based solar cells is investigated by means of simulations with realistic optical and electrical parameters of state-of-the-art CGS and CIGS cells. First, a monolithically stacked tandem CGS/CIGS structure is analysed, achieving efficiencies up to 20.3% under standard test conditions. Then, in order to reduce the effects of the parasitic sub-bandgap absorption, a wavelength-selective intermediate reflector is incorporated in the tandem, leading to efficiencies up to 20.8%. Finally, the concept of spectrum splitting is tested in a hybrid four-terminal configuration of dislocated CGS and CIGS cells, and efficiencies up to 22.5% are simulated. To indicate further possible improvements, all three concepts are also tested in optically and electrically idealised CGS/CIGS structures, indicating the potential of efficiencies up to 28%.

We developed an optical model for simulation and optimization of luminescent down-shifting (LDS) layers for photovoltaics. These layers consist of micron-sized phosphor particles embedded in a polymer binder. The model is based on ray tracing and employs an effective approach to scattering and photoluminescence modelling. Experimental verification of the model shows that the model accurately takes all the structural parameters and material properties of the LDS layers into account, including the layer thickness, phosphor particle volume concentration, and phosphor particle size distribution. Finally, using the verified model, complete organic solar cells on glass substrate covered with the LDS layers are simulated. Simulations reveal that an optimized LDS layer can result in more than 6% larger short-circuit current of the solar cell.

Diffusive dielectric materials such as white paint have been demonstrated as effective back reflectors in the photovoltaic technology. In this work, a one-dimensional (1D) optical modeling approach for simulation of white paint films is developed and implemented in a 1D optical simulator for thin-film solar cells. The parameters of white paint, such as the paint film thickness, the pigment volume concentration (PVC), and the pigment/binder refractive index ratio (RIR), are examined and optimized to achieve the required optical properties for back reflector application. The simulation trends indicate that white paint back reflectors with sufficient film thickness and higher PVC and RIR values exhibit improved reflectivity characteristics which results in an increased long-wavelength quantum efficiency of thin-film silicon solar cells. The simulation results based on the 1D model agree very well with the experimental data obtained from reflectance measurements of various white paint compositions and quantum efficiency measurements of amorphous silicon solar cells with white paint back reflectors.

This publisher’s note amends the author list and Acknowledgments of [Opt. Mater. Express5, 1295 (2015]. The author names were corrected online as of June 24, 2015: https://www.osapublishing.org/ome/abstract.cfm?uri=ome-5-6-1296.

The detection of biomolecules based on fluorescence measurements is a powerful diagnostic tool for the acquisition of genetic, proteomic and cellular information. One key performance limiting factor remains the integrated optical filter, which is designed to reject strong excitation light while transmitting weak emission (fluorescent) light to the photodetector. Conventional filters have several disadvantages. For instance absorbing filters, like those made from amorphous silicon carbide, exhibit low rejection ratios, especially in the case of small Stokes' shift fluorophores (e.g. green fluorescent protein GFP with λ exc = 480 nm and λ em = 510 nm), whereas interference filters comprising many layers require complex fabrication. This paper describes an alternative solution based on dielectric diffraction gratings. These filters are not only highly efficient but require a smaller number of manufacturing steps. Using FEM-based optical modelling as a design optimization tool, three filtering concepts are explored: (i) a diffraction grating fabricated on the surface of an absorbing filter, (ii) a diffraction grating embedded in a host material with a low refractive index, and (iii) a combination of an embedded grating and an absorbing filter. Both concepts involving an embedded grating show high rejection ratios (over 100,000) for the case of GFP, but also high sensitivity to manufacturing errors and variations in the incident angle of the excitation light. Despite this, simulations show that a 60 times improvement in the rejection ratio relative to a conventional flat absorbing filter can be obtained using an optimized embedded diffraction grating fabricated on top of an absorbing filter.

[EN] In thin-film silicon solar cells textured interfaces are introduced, leading to improved antireflection and light trapping capabilities of the devices. Thin-layers are deposited on surface-textured substrates or superstrates and the texture is translated to internal interfaces. For accurate optical modelling of the thin-film silicon solar cells it is important to define and include the morphology of textured interfaces as realistic as possible. In this paper we present a model of thin-layer growth on textured surfaces which combines two growth principles: conformal and isotropic one. With the model we can predict the morphology of subsequent internal interfaces in thin-film silicon solar cells based on the known morphology of the substrate or superstrate. Calibration of the model for different materials grown under certain conditions is done on various cross-sectional scanning electron microscopy images of realistic devices. Advantages over existing growth modelling approaches are demonstrated one of them is the ability of the model to predict and omit the textures with high possibility of defective regions formation inside the Si absorber layers. The developed model of layer growth is used in rigorous 3-D optical simulations employing the COMSOL simulator. A sinusoidal texture of the substrate is optimised for the case of a micromorph silicon solar cell. More than a 50 % increase in short-circuit current density of the bottom cell with respect to the flat case is predicted, considering the defect-free absorber layers. The developed approach enables accurate prediction and powerful design of current-matched top and bottom cell., The authors acknowledge the financial support from the European FP7 projects Silicon-Light (GA no. 2412777), the Integrated Infrastructure Initiative (312483-ESTEEM2) and the Slovenian Research Agency (P2-0197). The authors thank Christophe Ballif and Remi Biron from IMT EPFL, Neuchatel and Rafal E. Dunin-Borkowski from Institute for Microstructure Research, Research Centre Julich for their precious support to this work. M. Sever personally acknowledges the Slovenian Research Agency for providing PhD funding., Slovenian Research Agency (ARRS)