This PDF file contains the front matter associated with SPIE Proceedings Volume 9898 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Hexagonal sinusoidal nanotextures are well suited to couple light into silicon on glass at normal incidence, as we have shown in an earlier publication [K. Jäger et al., Opt. Express 24, A569 (2016)]. In this manuscript we discuss how these nanotextures perform under oblique incidence illumination. For this numerical study we use a rigorous solver for the Maxwell equations. We discuss nanotextures with periods between 350 nm and 730 nm and an aspect ratio of 0.5.

We investigate the integration of Al nanoparticle arrays into the anti-reflection coatings (ARCs) of commercial triple-junction GaInP/ In0.01GaAs /Ge space solar cells, and study their effect on the radiation-hardness. It is postulated that the presence of nanoparticle arrays can improve the radiation-hardness of space solar cells by scattering incident photons obliquely into the device, causing charger carriers to be photogenerated closer to the junction, and hence improving the carrier collection efficiency in the irradiation-damaged subcells. The Al nanoparticle arrays were successfully embedded in the ARCs, over large areas, using nanoimprint lithography: a replication technique with the potential for high throughput and low cost. Irradiation testing showed that the presence of the nanoparticles did not improve the radiation-hardness of the solar cells, so the investigated structure has proven not to be ideal in this context. Nonetheless, this paper reports on the details and results of the nanofabrication to inform about future integration of alternative light-scattering structures into multi-junction solar cells or other optoelectronic devices.

After more than 20 years of research on rear side gratings for light trapping in solar cells, we have been able to demonstrate enhanced efficiencies for crystalline silicon solar cells with two different grating concepts and solar cell architectures. In both cases planar front sides have been used. With hexagonal sphere gratings and the tunnel oxide passivated contact (TOPCon) concept, a grating induced J_sc increase of 1.4 mA/cm² and an efficiency increase of 0.8%absolute could be achieved. With binary crossed gratings fabricated by a nanoimprint based process chain, a grating induced J_sc gain of 1.2 mA/cm² and an efficiency gain of 0.7% absolute could be achieved. For the binary grating concept, cell thickness variations have also been performed. The increasing importance of the light trapping properties towards low solar cell thicknesses could be confirmed by an enhanced EQE in the long wavelength region (J_sc increase: 1.6 mA/cm² for 150 μm and 1.8 mA/cm² for 100 μm thick solar cells). The results are in very good agreement with simulations using the OPTOS modeling formalism. OPTOS enables the further analysis and optimization of grating concepts in silicon solar cells and modules. So a grating induced J_sc gain of 0.8 mA/cm² is forecast for solar cells with pyramidal front side texture. On module level, still a grating induced J_sc gain of 0.6 mA/cm² can be expected.

Device modelling and characterization are indispensable tools in the design of photovoltaic devices. In the contribution we present two challenging issues related to accurate modelling and efficient characterization of light scattering at nanotextured interfaces or other nanophotonic structures used in solar cell technologies. The model based on finite element method, which is upgraded with the Huygens’ expansion theorem is presented. It enables to calculate the angular distribution function of scattered light in the near and far field. It accounts also for the antireflection effects originating from nanoroughnesses. To characterize scattered light efficiently a camera based angular resolved spectroscopy system is presented. It captures the spatial angular distribution function in broad angular range at one shot.

Surface textures can significantly improve anti-reflective and light trapping properties of silicon solar cells. Combining standard pyramidal front side textures with scattering or diffractive rear side textures has the potential to further increase the light path length inside the silicon and thereby increase the solar cell efficiency. In this work we introduce the OPTOS (Optical Properties of Textured Optical Sheets) simulation formalism and apply it to the modelling of silicon solar cells with different surface textures at front and rear side. OPTOS is a matrix-based method that allows for the computationally-efficient calculation of non-coherent light propagation within textured solar cells, featuring multiple textures that may operate in different optical regimes. After calculating redistribution matrices for each individual surface texture with the most appropriate technique, optical properties like angle dependent reflectance, transmittance or absorptance can be determined via matrix multiplications. Using OPTOS, we demonstrate for example that the integration of a diffractive grating at the rear side of solar cells with random pyramids at the front results in an absorptance gain that corresponds to a photocurrent density enhancement of 0.73 mA/cm² for a 250 μm thick cell. The re-usability of matrices enables the investigation of different solar cell thicknesses within minutes. For thicknesses down to 50 μm the simulated gain increases up to 1.22 mA/cm². The OPTOS formalism is furthermore not restricted with respect to the number of textured interfaces. By combining two or more textured sheets to effective interfaces, it is possible to optically model a complete photovoltaic module including EVA and potentially textured glass layers with one calculation tool.

Barium di-silicide (BaSi₂) is an abundant and inexpensive semiconductor with appealing opto-electrical properties. In this work we show that a 2-μm thick BaSi₂-based thin-film solar cell can exhibit an implied photo-current density equal to 41.1 mA/cm², which is higher than that of a state-of-the-art wafer-based c-Si hetero-junction solar cell. This performance makes BaSi₂ an attractive absorber for high-performing thin-film and multi-junction solar cells. In particular, to assess the potential of barium di-silicide, we propose a thin-film double-junction solar cell based on organometallic halide perovskite (CH₃NH₃PbI₃) as top absorber and BaSi₂ as bottom absorber. The resulting modelled ultra-thin double-junction CH₃NH₃PbI₃ / BaSi₂ (< 2 μm) exhibits an implied total photo-current density equal to 38.65 mA/cm² (19.84 mA/cm² top cell, 18.81 mA/cm² bottom cell) and conversion efficiencies up to 28%.

The paper demonstrates a rigorous modeling approach for 1D microstructured absorbing multi-layers for the receivers of CSP (Concentrated Solar Power), taking into account both absorption of the incident solar energy and the emissivity while considering receivers temperature. From an optimized multilayers structure achieving high absorption, the authors demonstrate that 1D sub wavelength period gratings could increase further the absorption and thus the yield of the Concentrated Solar Power system. The authors used C-method (Chandezon Method) to optimize 1D grating profile. Experimental demonstration on Silicon wafers combining writing grating and absorptive layers deposition are also presented. Experimental results are presented and absorbance enhancement of almost 2% are achieved with values of 96.5% in the visible and UV range. The results are promising for the design of future and competitive solar absorbers for CSP since the microstructuring fabrication approach can be applied to non-planar substrates such as tubes, which are the receivers of the CSP.

In this work we developed a new approach for resistivity measurements based on fs laser micro machining of μ-TLM test structures. This method is applied to highly resistive interfacial and conductive bulk multilayer systems in photovoltaic TCO thin film devices. Resistivity data has been acquired by a new TLM based method at μm-dimensions (μ-TLM, patent pending, DE 102014211352.0). For this approach, isolating trenches are prepared in the µm range with reasonable effort using fs laser processing. The application of ultrashort pulses with a laser wavelength in the IR range (λ = 1.03 μm) allows selective removal of the top SnO₂ layer of the TCO multilayer stack by a reduced thermal influence on the layers beneath and in the adjacent region of the laser trenches. Small effective optical penetration and ablation depth was achieved by an ultrafast thermal ablation mechanism via free carrier absorption at the interface of the SnO₂/ITO layers. Therefore the risk of laser induced modification of the electric layer properties is negligible. The μ-TLM test structure results in highly accurate and reproducible resistivity data. Applied to SnO₂/ITO/glass double layer stacks, the obtained resistivity values for the SnO₂ interfacial layer (ρTO = 40.5 kΩμm) and for the indium tin oxide thin film (ρITO = 1.3 Ωμm) agree with reference data from four-point-probing and from literature.

Eco-friendly and sustainable power generation is one of the important aims of our time. Harvesting renewable energy can, e.g., be done by solar cells. For the integration in textiles, developing solar cells with typical textile haptics and pliability would be ideal. Additionally, textile solar cells should be created from low-purity materials in low-cost processes to be compatible with the textile industry. Thus, dye sensitized solar cells are ideal candidates for the integration of solar cell technology into textiles. In a recent project, we systematically test different material systems applied on textiles in which all functional layers are varied. One of the most crucial points is the sintering process of TiO₂ which is only possible on a few textile materials. Additionally, the TiO₂ coating itself contains the risk of being not completely isolating, allowing for dye and electrolyte or textile fibers penetrating through this layer and reaching the front electrode. This can result in short circuits or undesired counteracting voltages and currents. The article shows how different coating and sintering technologies of TiO₂ on glass and textile fabrics influence the structures of the respective layers on different scales. It illustrates the differences between glass and textile fabrics in terms of the coating process and the resulting layer properties. Time-dependent measurements of open-circuit voltages and efficiencies show the physical implications of variations of the TiO₂ layer structure and the resulting inner surfaces. In this way, we depict the different effects arising from undesired modifications of the TiO₂ layer structure.

Optical and electrical properties (Haze spectra, carrier concentration, mobility, resistivity) of zinc oxide thin films deposited on glass substrates were studied by plasma treatment and by thermal annealing. Films of copper oxides on the glass and CuO/ZnO structures were formed by vacuum deposition of copper films followed by thermal annealing in air. Optical and structural properties of the CuO films and electrical properties of ZnO/CuO structures were investigated upon thermal treatment. It is shown that a photosensitive n-ZnO/p-CuO heterojunction may be formed by rapid (~1 min) thermal processing in air.

Solar cells have low efficiency and non-linear characteristics. To increase the output power solar cells are connected in more complex structures. Solar panels consist of series of connected solar cells with a few bypass diodes, to avoid negative effects of partial shading conditions. Solar panels are connected to special device named the maximum power point tracker. This device adapt output power from solar panels to load requirements and have also build in a special algorithm to track the maximum power point of solar panels. Bypass diodes may cause appearance of local maxima on power-voltage curve when the panel surface is illuminated irregularly. In this case traditional maximum power point tracking algorithms can find only a local maximum power point. In this article the hybrid maximum power point search algorithm is presented. The main goal of the proposed method is a combination of two algorithms: a method that use temperature sensors to track maximum power point in partial shading conditions and a method that use illumination sensor to track maximum power point in equal illumination conditions. In comparison to another methods, the proposed algorithm uses correlation functions to determinate the relationship between values of illumination and temperature sensors and the corresponding values of current and voltage in maximum power point. In partial shading condition the algorithm calculates local maximum power points bases on the value of temperature and the correlation function and after that measures the value of power on each of calculated point choose those with have biggest value, and on its base run the perturb and observe search algorithm. In case of equal illumination algorithm calculate the maximum power point bases on the illumination value and the correlation function and on its base run the perturb and observe algorithm. In addition, the proposed method uses a special coefficient modification of correlation functions algorithm. This sub-algorithm uses the error value between calculated and real maximum power point and on its base modifies correlation function coefficients.

Although organic solar cells show intriguing features such as low-cost, mechanical flexibility and light weight, their efficiency is still low compared to their inorganic counterparts. One way of improving their efficiency is by the use of light-trapping mechanisms from nano- or microstructures, which makes it possible to improve the light absorption and charge extraction in the device’s active layer. Here, periodically arranged colloidal gold nanoparticles are demonstrated experimentally and theoretically to improve light absorption and thus enhance the efficiency of organic solar cells. Surface-ordered gold nanoparticle arrangements are integrated at the bottom electrode of organic solar cells. The resulting optical interference and absorption effects are numerically investigated in bulk hetero-junction solar cells based on the Finite-Difference Time-Domain (FDTD) and Transfer Matrix Method (TMM) and as a function of size and periodicity of the plasmonic arrangements. In addition, light absorption enhancement in the organic active layer is investigated experimentally following integration of the nanoparticle arrangements. The latter are fabricated using a lithography-free stamping technique, creating a centimeter scaled area with nanoparticles having a defined inter-particle spacing. Our study reveals the light harvesting ability of template-assisted nanoparticle assemblies in organic solar cells. As the approach is easily scalable, it is an efficient and transferable method for large-scale, low cost device fabrication.

The paper presents a new algorithm that uses a combination of two models of BRDF functions: Torrance-Sparrow model and HTSG model. The knowledge of technical parameters of a surface is especially useful in the construction of the solar concentrator. The concentrator directs the reflected solar radiation on the surface of photovoltaic panels, increasing the amount of incident radiance. The software applying algorithm allows to calculate surface parameters of the solar concentrator. Performed simulation showing the share of diffuse component and directional component in reflected stream for surfaces made from particular materials. The impact of share of each component in reflected stream on the efficiency of the solar concentrator and photovoltaic surface has also been described. Subsequently, simulation change the value of voltage, current and power output of monocrystalline photovoltaic panels installed in a solar concentrator system has been made for selected surface of materials solar concentrator.

In this work we develop an algorithm to determinate the accuracy of the Null-Screen Method, used for the testing of flat heliostats used as solar concentrators in a central tower configuration. We simulate the image obtained on a CCD camera when an orderly distribution of points are displayed on a Null-Screen perpendicular to the heliostat under test. The deformations present in the heliostat are represented as a cosine function of the position with different periods and amplitudes. As a resolution criterion, a deformation on the mirror can be detected when the differences in position between the spots on the image plane for the deformed surface as compared with those obtained for an ideally flat heliostat are equal to one pixel. For 6.4μm pixel size and 18mm focal length, the minimum deformation we can measure in the heliostat, correspond to amplitude equal a 122μm for a period equal to 1m; this is equivalent to 0.8mrad in slope. This result depends on the particular configuration used during the test and the size of the heliostat.

Two Organic Photovoltaic devices having a photoactive layer containing Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5- (4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM, 99%), and the layer sequences – glass/ITO/ZnO/PAL/PEDOT:PSS/Ag/encapsulation were non-destructively investigated by diffuse optical spectral reflectance, THz spectroscopy and THz imaging. The proposed methods proved to be powerful tools to support quality assurance in organic solar cells development, facilitating both the localization of manufacturing defects and the device degradation, as they are combined with “classical” evaluation means.

The passivation of silicon surfaces play an important role for achieving high-efficiency crystalline silicon solar cells. In this work, a stack system comprising of 20nm Al₂O₃ with a 22nm TiO₂ topping layer was deposited on p-type Si using thermal atomic layer deposition (ALD) and was investigated regarding its passivation quality. Quasi-steady-state photo conductance (QSSPC) measurements reveal that the minority carrier lifetime at an injection density of 1015cm⁻³ increased from 1.10ms to 1.96ms after the deposition of TiO₂, which shows that the deposition of TiO₂ onto Al₂O₃ is capable of enhancing its passivation quality. Capacity voltage (CV) measurements show that the amount of negative charges in the dielectric layer has increased from -2.4·10¹²cm⁻² to -6.3·10¹²cm⁻² due to the deposition of TiO₂. The location of the additional charges was analyzed in this work by etching the dielectric layer stack in several steps. After each step CV measurements were performed. It is found that the additional negative charges are created within the Al₂O₃ layer. Additionally, ToF-SIMS measurements were performed to check for diffusion processes within the Al₂O₃ layer.