This PDF file contains the front matter associated with SPIE Proceedings Volume 10688, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Silicon based multi-junction solar cells are a promising option to overcome the theoretical efficiency limit of a silicon solar cell (29.4%). With III-V semiconductors, high bandgap materials applicable for top cells are available. For the application of such silicon based multi-junction devices, a full integration of all solar cell layers in one 2-terminal device is of great advantage. We realized a triple-junction device by wafer-bonding two III-V-based top cells onto the silicon bottom cell. However, in such a series connected solar cell system, the currents of all sub-cells need to be matched in order to achieve highest efficiencies. To fulfil the current matching condition and maximise the power output, photonic structures were investigated. The reference system without photonic structures, a triple-junction cell with identical GaInP/GaAs top cells, suffered from a current limitation by the weakly absorbing indirect semiconductor silicon bottom cell. Therefore rear side diffraction gratings manufactured by nanoimprint lithography were implemented to trap the infrared light and boost the solar cell current by more than 1 mA/cm². Since planar passivated surfaces with an additional photonic structure (i.e. electrically planar but optically structured) were used, the optical gain could be realized without deterioration of the electrical cell properties, leading to a strong efficiency increase of 1.9% absolute. With this technology, an efficiency of 33.3% could be achieved.

Perovskite silicon tandem solar cells can overcome the efficiency limit of single junction silicon solar cells. Optical modeling plays a crucial role for the device optimization but it becomes complex if optically thin and thick layers as well as interface textures, such as random pyramids, are involved. Within this work, the OPTOS simulation formalism is applied in order to compare perovskite silicon tandem solar cells with planar and textured front side. Modeling the configuration with planar front side and textured rear exhibits a matched photocurrent density of 18.2 mA/cm². For the system with textured front and planar rear side the reduced reflectance leads to a photocurrent density of 19.6 mA/cm² although parasitic absorption in the Spiro-OMeTAD and ITO layers increases. Taking into account the full module stack in the OPTOS simulation shows an increased front side reflectance and parasitic absorption in the EVA. The difference between the resulting photocurrent densities (17.8 mA/cm² and 18.9 mA/cm²) demonstrates the optical superiority of the investigated system with textured front side not only at cell level but also in the full module stack.

Recently, we studied the effect of hexagonal sinusoidal textures on the reflective properties of perovskite-silicon tandem solar cells using the finite element method (FEM). We saw that such nanotextures, applied to the perovskite top cell, can strongly increase the current density utilization from 91% for the optimized planar reference to 98% for the best nanotextured device (period 500 nm and peak-to-valley height 500 nm), where 100% refers to the Tiedje-Yablonovitch limit.* In this manuscript we elaborate on some numerical details of that work: we validate an assumption based on the Tiedje-Yablonovitch limit, we present a convergence study for simulations with the finite-element method, and we compare different configurations for sinusoidal nanotextures.

Silicon solar cells are typically textured by means of wet chemical etching in order to enhance absorption. Within this work, we apply an optically functional layer onto a planar silicon surface. This layer is made of a high refractive index sol-gel material and can be patterned by nanoimprint lithography (NIL). In first experiments, we investigated various sol-gel based TiO₂ precursors and evaluated their refractive index as well as the possibility to apply them in NIL. The refractive index was determined to be up to 2.25 using ellipsometry. This result was achieved with a solution composed of amorphous TiO₂ precursors mixed with ethanol and 1,5-pentanediol. The topography of the patterned TiO₂ layers were investigated using an atomic force microscope (AFM) and a scanning electron microscope (SEM) revealing a period of 1 μm and a pattern depth of 60 nm after sintering. Furthermore, optical modeling was used to optimize the structure parameters in order to minimize the weighted reflectance of an encapsulated silicon solar cell.

In the built environment there is an increasing issue of heat management, with buildings expending significant energy resources to maintain comfortable living temperatures. In many parts of the world, this entails the use of both heating and cooling during daylight hours depending on ambient temperatures. Due to the variation in the desired temperature control classical solutions can become counter productive in their aim of maintaining comfortable temperatures, therefore it is important to employ adaptive solutions that vary their functionality based on circumstance, such as window films with thermochromic or electrochromic properties. Here, we present a design for a thermochromic smart window film based on a multilayer stack of silica, titania and vanadium dioxide (VO₂). The design makes use of coherent interference within the multi-layered structure to suppress the typically high reflection of visible light and improve the reflective component of solar modulation. This allows us to simultaneously improve the visible transmittance and solar modulation of the film above what would be possible with a single layer of vanadium dioxide film. Guided by simulation, the multilayer structure is fabricated using a scalable sol-gel method and results are compared with simulations and a single layer VO₂ reference sample.

With commercial silicon solar cells approaching both practical and theoretical efficiency limits, there is growing research effort to develop new low-cost technologies capable of reaching efficiencies of 30% and beyond. Silicon-based tandems that combine current industrial technology with emerging thin-film PV materials are considered the most cost-effective option for achieving this, with the latest edition of the International Technology Roadmap for Photovoltaics (ITRPV) predicting Si-based tandems to appear in mass production after 2019. The rapid rise of perovskite solar cell performance in the past few years has made perovskites the material of choice as a top cell for such tandems due to their high efficiency and simple, low-cost fabrication. Optimization of tandems requires detailed knowledge and characterization of the optical and electrical properties of every layer, as well as practical constraints imposed by processing sequences and chemical incompatibilities. This presentation will review the latest progress in perovskite-silicon tandems, including our recent demonstration of a 26.4% 4-terminal tandem, and a 22.8% monolithic tandem based on a diffused-junction silicon homojunction cell. Key challenges and potential pathways for reaching efficiencies of 30% and beyond will be identified and discussed.

Thermalization and lack of absorption inherently form the main energy losses of any single-junction solar cell, limiting the power conversion efficiency. As is well known, this ‘quantum defect’ problem can be partially solved when different bands of the solar spectrum are distributed over multiple different absorber layers with corresponding bandgaps. In this fashion, conventional vertically-stacked, series-connected tandems have shown to reach higher efficiencies than single-junction solar cells. However, the inherent problems of this geometry are the need for current-matching, transparent intermediate (electrode) layers and, in some geometries, epitaxial growth constraints of the subsequent layers. In addition, fabrication of (epitaxial) layer stacks is expensive and not always compatible with large-scale processing. A parallel-stacked geometry, in which individual solar cells are placed next to each other, could overcome these problems. Such a geometry requires a spectrum-splitting mechanism to guide different spectral bands of the incoming sunlight to the cells with corresponding bandgap [1]. Here, we introduce a tapered dielectric waveguide geometry in which light is coupled out when the waveguide thickness reaches the cut-off condition at a given wavelength. Numerical finite-difference time domain (FDTD) simulations show that the light that is coupled out of the tapered waveguide is spatially separated as a function of wavelength. Light in the 850-1150 nm spectral band is mostly coupled out of the first section of the tapered waveguide, while the 450-850 nm spectral band is coupled out of the last section of the waveguide. Choosing readily available (thin film) Si and GaAs solar cells underneath such a tapered waveguide, only light with energy lower than the GaAs bandgap (~892 nm) reaches the Si subcell, while most of the light with higher energy reaches only the GaAs subcell. This geometry benefits from both a reduction of the ‘quantum defect’ losses and a concentration factor for both subcells. We fabricate tapered waveguides by e-beam physical vapor deposition (EB PVD) of TiO2 onto a silica glass substrate using a moving shutter during evaporation. Light is coupled into the waveguide using a confocal microscope and optical transmission spectroscopy is used to measure the outcoupling spectrum as a function of position along the tapered waveguide. In addition, Fourier spectroscopy is used to determine the outcoupling angle as a function of wavelength at each position. The tapered geometry is then placed on top of Si and GaAs solar cells and the power coupled into each cell is measured as a function of wavelength. The distribution of light over the subcells can be optimized by controlling the precise tapering geometry. In a further advanced design, the tapered waveguides are integrated with light concentrating optical troughs that couple light into the waveguide taper. [1] A. Polman and H. A. Atwater, “Photonic design principles for ultrahigh-efficiency photovoltaics,” Nat. Mater., vol. 11, no. 3, pp. 174–177, 2012.

Efficiency of state-of-the-art single-junction solar cells is approaching the Shockley-Queisser limit (c-Si, GaAs). In contrast, the thickness of state-of-the-art solar cells is far from its theoretical limits and could be reduced by more than one order of magnitude with efficient light-trapping. In this talk, I first present a benchmark of recent advances of ultra-thin solar cells (c-Si, CIGS, GaAs), using short-circuit current as a function of absorber thickness. I show that current state-of-the-art solar cells operate close to single-pass absorption and I highlight different light-trapping strategies proposed in the literature to approach the Lambertian limit. I then introduce our strategy for efficient light-trapping based on multi-resonant absorption. This approach overcomes the 4n2 limit, making use of coherent scattering of a discrete number of resonant modes. In the second part, I apply these concepts to CIGS and GaAs solar cells. The goal is to reduce the thickness of the semiconductor absorber by one order of magnitude while preserving the short-circuit current. This study is not only pertinent from an academic point of view, but is of practical relevance to CIGS manufacturers for reducing material consumption and time deposition and for space power applications, where ultra-thin solar cells based on III-V semiconductors outperform long-term efficiency and power production of thicker cells due to their intrinsically higher radiation tolerance. We propose a simple and scalable light-trapping architecture based on nanostructured TiO2/silver back-mirror fabricated by direct nanoimprint of sol-gel derived films over large surface areas. Electromagnetic simulations predict a short-circuit current of 36.3 mA/cm2 for a 150 nm thick CIGS solar cell, and I present our roadmap for implementing these concepts in an industrial CIGS solar cell fabrication process. Finally, I detail the design and fabrication of a 205 nm thick GaAs solar cell featuring certified efficiency of 19.9%, and I discuss possible improvements to achieve 25% efficiency.

We design reflective resonant metasurfaces that enable highly efficient wavefront shaping with arbitrary scattering pattern, based on the recently introduced metagrating concept [1]. Using finite-sized arrays of suitably tailored optical antennas placed above a reflective ground plane, we create an omnidirectional Lambertian light scattering geometry that can find applications in colorful photovoltaics [2]. Supercells of metagratings with close-to-unity efficiency can be combined in arrays to shape any desired wide-angle scattering pattern, creating a novel way to design light trapping geometries for photovoltaics. Metagratings, recently introduced in [1], employ as a starting point the known physics of grating scattering, in which the period determines a discrete set of diffraction orders, and enables additional control over the scattering characteristics by using resonant bianisotropic light scatterers as the elements forming the grating. The carefully engineered scatterers are arranged above a reflecting ground plane with a distance such that interference of scattering and ground plane reflection in the far field causes the incident power to be rerouted towards the desired grating orders. The scattered light can be directed with unitary efficiency into a single diffraction order, or divided at will into multiple diffraction orders. We apply the metagrating concept to realize a Lambertian angular light scattering distribution, in which light is scattered over a broad angular range according to I(θ)=I_0 cos⁡θ. The surface is composed of supercells, each of which includes a small number of subcells formed by metagrating elements. In this configuration, each supercell is tuned to scatter light with a specific angular dependency and scattering efficiency. Together, the supercells form a metagrating that scatters an incident beam to a Lambertian scattering profile. We find that efficient angular control is already achieved for a small number of scatterers (N~5-12) in each supercell. As a result, the total size of the structure is smaller than 40 micrometers, enabling the creation of a homogenous Lambertian scattering appearance in the far field for photovoltaic applications. Our initial Lambertian metasurface design is based on analytical antenna theory in which the far-field scattering pattern is calculated using magnetic dipoles as scattering elements. The optimized scattering patterns were found using an analytical optimization procedure. In a more advanced design, we implemented resonant light scattering elements with a magnetic response, which can be experimentally realized using dielectric nanoparticles with a magnetic Mie resonance or plasmonic metallic nanoparticles. These metasurfaces are designed to show Lambertian scattering in a well-defined spectral band, determined by the bandwidth of the Mie/plasmonic resonance. The resonant Lambertian metasurface design presented here enables the creation of artificial surfaces with a matt colored appearance. This is a major step forward compared to nanopatterned solar cells that we presented earlier that showed colored specular reflection [2]. The new designs will enable many other applications where controlled beam steering in ultrathin optical devices is needed, specifically for light trapping in thin-film solar cells, and spectrum splitting in parallel and series-connected multi-junction architectures. The proposed metagrating designs create full control over the angular distribution of light scattering in ways that cannot be achieved with dielectric or plasmonic scatterers alone. This work therefore is a major step beyond the work on light management using resonant light scatterers performed so far. [1] Ra’di Y., Sounas D., and Alù A., Metagratings: Beyond the limits of graded metasurfaces for wavefront control, Phys. Rev. Lett. 119, 067404 (2017). [2] Neder V., Luxembourg S.L., and Polman A., Efficient colored silicon solar modules using integrated resonant dielectric nanoscatterers, Appl. Phys. Lett. 111, 073902 (2017).

Structured Silicon layers are used to improve light harvesting by Si-based solar cells. Microstructure of Si is obtained by a selective Si etching using aggressive solvents (acids like HF). In the approach discussed in this work a simplified architecture of solar cells is discussed. A structured electrode is formed by deposition of ZnO nanorods on top of p-type Si. This modification eliminates energy consuming and environmental unfriendly technological steps, as discussed. The so-obtained 3D top electrode consists of n-type ZnO:Al (AZO) layer grown on ZnMgO coated zinc oxide nanorods. AZO and ZnMgO films are deposited by Atomic Layer Deposition method (ALD). Advantages of this technique are first discussed. Several possible applications of the ALD are reviewed.

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.

Over the last couple of years, photonic materials with tailored -i.e. with deliberately introduced- structural disorder have attracted considerable interest in photovoltaics due to their extended spectral and angular range of effectiveness [1]. Notably, quasi-random nanostructures realized by e-beam lithography (EBL) have been integrated in solar cells as broadband light trapping elements, and have proved to approach the theoretical (Lambertian) limit [2]. Despite recent research efforts aiming at increasing the EBL writing speed [3], alternative routes based on self-assemblies still possess major advantages for an industrial implementation of disordered structures as they allow to rapidly process them over large areas (>>cm2). In this communication, we show that the up-scalable polymer blend lithography technique can be used as a versa-tile platform for fabricating 2D planar, disordered nanostructures that can be exploited in both top-down and bottom-up strategies. Tailored disorder is achieved here by adjusting the process parameters (polymer blend composition and deposition conditions), enabling to tune the morphology and the spatial distribution of the nanostructures produced, and in turn their light harvesting properties. We first use our approach to pattern a resist etching mask, which is employed for transferring disordered nanoholes into a thin hydrogenated amorphous silicon layer by dry etching (top-down route). We report an enhancement of its integrated absorption of +90% under normal incidence, and of up to +200% at large incident angles with respect to an unprocessed absorber [4]. In a second example, we demonstrate that similar structures can serve as a template in a bottom-up configuration, whereby copper indium diselenide nanocrystals are infiltrated into the disordered nano-holes formed in a resist layer. This route, paving the way to wet-processable "photonized" absorbers, is compared to a previous work relying on a serial writing process [5], and the optical properties of the resulting patterned absorbing layers are analysed. We finally elaborate on the significance of these findings for the reverse problem, namely for light extraction in broadband light-emitting diodes. References [1] Burresi, M., Pratesi, F., Riboli, F., & Wiersma, D. S. (2015). Complex photonic structures for light harvesting. Advanced Optical Materials, 3(6), 722-743. [2] Martins, E. R., Li, J., Liu, Y., Depauw, V., Chen, Z., Zhou, J., & Krauss, T. F. (2013). Deterministic quasi-random nanostructures for photon control. Nature communications, 4, 2665. [3] Li, K., Li, J., Reardon, C., Schuster, C. S., Wang, Y., Triggs, G. J., ... & Krauss, T. F. (2016). High speed e-beam writing for large area photonic nanostructures—a choice of parameters. Scientific reports, 6. [4] Siddique, R. H., Donie, Y. J., Gomard, G., Yalamanchili, S., Merdzhanova, T., Lemmer, U., & Hölscher, H. (2017). Bioinspired phase-separated disordered nanostructures for thin photovoltaic absorbers. Science Advances, 3(10), e1700232. [5] Dottermusch, S., Quintilla, A., Gomard, G., Roslizar, A., Voggu, V. R., Simonsen, B. A., ... & Richards, B. S. (2017). Infiltrated photonic crystals for light-trapping in CuInSe2 nanocrystal-based solar cells. Optics Express, 25(12), A502-A514.

An essential device in opto-electronics is the optical waveguide. In the following we present a way to incorporate a waveguide field source into numerical time-domain simulations via the total field/scattered field technique. In particular, we develop a method by which we introduce a Gaussian light-pulse with the real eigenmodes of a slab waveguide into the nodal discontinuous Galerkin time-domain scheme.

Integrated nanophotonic circuits allow for realizing complex optical functionality in a compact and reproducible fashion through high-yield nanofabrication. Typically configured for single-mode operation in a single path, the optical propagation direction in such devices is determined by the waveguide layout which inherently requires smooth surfaces without scattering and restricts the device footprint to the limits of total internal reflection. Yet intentionally introducing disorder and scattering can be beneficial for the realization of novel nanophotonic components to overcome fabrication imperfections. Therefore, the understanding of the underlying physics of randomly disordered nanophotonic systems has gained increased attention. In particular on-chip spectrometers may benefit from random disorder. These devices are widely used tools in chemical and biological sensing, materials analysis and light source characterization. Conventional nanophotonic spectrometer designs are based on concepts using ring resonators, arrayed waveguide gratings or echelle gratings. Those devices are based on careful design and rely on high control of the fabrication and are therefore prone to fabrication errors and exhibit a very large footprint. Here, as part of the priority program “Tailored Disorder” (SPP 1839), we utilize multi-path interference and the interaction of light with randomly oriented scatterers to realize broadband and narrow linewidth on-chip integrated spectrometers with small footprint. In combination with integrated superconducting nanowire single-photon detectors such devices allow for resolving optical spectra on the single photon level which is of interest for single-photon spectroscopy or quantum wavelength division multiplexing.

The article presents a tracking system controller that tracks apparent position of the Sun on celestial sphere. The device does not require any operating by user. Applying the GPS module, gyroscope, magnetometer and accelerometer ensures the autonomy of device. In controller was implemented authorial algorithm which on the basis of collected data automatically selects appropriate value of inclination angle the photovoltaic surface in relation to direction of incidence solar radiation and resolution step tracking system. The efficiency analysis of the presented system was performed depending on sunlight conditions. Then, the device was compared with the analogical solution that does not use the authorial algorithm. The results of simulations showed that this tracking controller allows to increase in the power output of photovoltaic panels from 4% to 7%.

This paper presents Monte Carlo simulations of the time-of-flight measurement for a unidimensional lattice of an organic semiconductor sample, under Gaussian Disorder Model assumptions, in which charge carriers follow a hopping transport mechanism. Mobilities for different values of the applied electric field have been computed, and the power conversion efficiency of the sample is determined as a function of the electric field. With the extracted data, it is shown that there is an optimal field value at which high mobility and efficiency can be obtained.

As direct band gap semiconductor, CIGS thin film solar cells has developed rapidly in recent years. Nano-ripples on transparent layer of CIGS solar cells can improve the light absorption. The photoelectric conversion efficiency improved and the thickness of solar cell decreased with the requirement of optical absorptivity. This study proposed a key technological point concerning the obtainment of perfect LIPSSs using picosecond laser with different beam pattern. Linear sweep in parallel to the laser polarization direction was performed using a Nd:VAN laser system with 10-ps Qswitched pulsed at a central wavelength of 532 nm with a repetition rate of 1 kHz. The nanostructure with different characteristics were obtained at different laser fluence and scanning speed which was focused with circular spot. The linear spot pattern can improve the processing efficiency greatly. In this way, three kind of morphologies were obtained successfully at the same parameter, which was useful for processing different kind of nanostructures. To our knowledge, it is the first time that we report the LIPSSs formed on CIGS absorber layers. Thus, the proposed technique can be considered to be a promising method for the laser machining of special nonmetal films.

Antireflective coatings have been used for reducing light reflection in many optoelectronic devices. Using these coating with thin _lm CZTS solar cell, would increase its low efficiency and make it a good alternative for bulk solar cells. Designing optimum antireflective coating requires to control light scattering directivity from subwavelength nanostructures. Mie theory could calculate absorption and scattering cross section of different nanoscatters on CZTS substrate, and it is enables us in understanding role of electric and magnetic dipoles in reducing light reflection from coated surface. Our approach is using concept of Mie theory to make design methodology for fast predicting optimum plasmonic nanoscatters dimension for lowest light reflection. Then, we swept on periodicity for examining light coupling dependency on pitch. Moreover, we made coating for plasmonic nanoscatters with dielectric materials to study possible enhancements from plasmonic and dielectric on same scatter. Our results indicate possibility of controlling absorption and scattering cross section of plasmonic nanoscatters with changing its dimensions and pitch. Also, using dielectric coating could enhance the light coupling performance over planar CZTS substrate. We suggested some nanoscatters with certain dimensions to achieve highest enhancement in light absorption inside CZTS solar cells. All calculations of this work built based on Mie theory. For verification of our results, we start by modelling of silver sphere on substrate and it gave a very good matching with previously reported work. Integrating antireflective coating with CZTS solar cells would open the door for increasing its overall efficiency beyond current limit.

Efficiency of CZTS solar cell has made it a good candidate for low cost thin _lm solar cells, due to its low cost and earth abundant materials. Though, its efficiency barely reach 12.6% in 2013, which let great room of improvements required in its efficiency, this could be achieved using plasmonic scattering nanostructures. Designing and selecting optimum plasmonic scattering nanostructures inside active layer of CZTS solar cells would enhance light absorption and increase generated photocurrent. Using Mie theory, we could calculate absorption and scattering cross sections for any plasmonic nanostructure inside solar cells. Calculating and controlling absorption and scattering peaks would manipulate light propagation direction for highest light concentration in CZTS active layer. According to our results, we found that absorption and scattering efficiency of silver nanostructures could be controlled for enhancing light coupling over planar structure only. In addition, using dielectric coating would enhance scattering efficiency and generated more photocurrent over planar structure. All modeling done during this work made using three-dimensional finite element method simulation tool. To verify our results, we compared theoretical results of silver sphere over substrate with previous reported work, and good matching achieved. Using proposed plasmonic nanoscattering structures with certain dimension, pitch, and coating thickness would enhance overall efficiency of CZTS solar cells.

Thin film solar cells based on CZTS (Cu₂ZnSnS₄) have record efficiency in 2013 around 12.6%. Its materials are low cost, non-toxic and earth abundant and this makes it suitable low cost solar cells. Enhancing its efficiency over this limit could be achieved using nanophotonic techniques for guiding light. Our approach here is designing optimum back contact plasmonic nanostructure for increasing light trapping based on Mie theory. Using Mie theory parameters, we could identify position of electric and magnetic dipoles, absorption and scattering efficiency of different nanostructures, and select optimum nanostructure for highest back scattering light and light trapping. Our design methodology for selecting optimum back contact nanostructure includes reducing absorption efficiency, increasing scattering efficiency, and increasing back scattered light. Our simulation results indicate that, light trapping is totally depending on dimension and pitch of closed plasmonic nanostructure, a good enhancement in light trapping achieved using plasmonics structures, after using dielectric coating we found enhancement in generated photocurrent over planar back contact. In addition, our results give clearer picture about how absorption and scattering efficiency of each proposed nanostructure would change back scattered light ratio. For more accurate results, we have done all our simulations using three-dimensional models based on finite element method tool. For verifying our results, we started comparing our results of plasmonic nanostructure over substrate with previous reported work, and results matched accurately. Fabricating optimum gold nanostructure with dielectric coating over back contact of CZTS would result in increasing light trapping and its overall efficiency.

Solar heat reflective paint coated roof is known as cool roof. These cool roofs have an ability of saving energy consumption due to its high reflection against solar irradiation. However, it is suggested that these cool roofs should not be used at cold area because its reflection makes temperature of walls lower. These cool roofs should absorb a solar irradiation when cold situation to raise energy efficiency. Therefore, both reflection and absorption compatible roof is needed. This characteristic can be obtained from active or a passive characteristics-modulating technics. In this study, we focused on the geometrical relationship between the Sun and the Earth, and angular variation of reflection by microstructure. We calculated an angular solar irradiance distribution at the Earth’s arbitrary point from theoretical model and numerically analyzed an angular selective reflective microstructure at single wavelength using Rigorous coupled wave analysis (RCWA) method to verify possibility of angle-selectivity. A microstructure was optimized to its effective reflectivity and absorptivity by changing its geometrical parameters. The optimized microstructure works as the surface has 71% reflector during summer solstice while works as a 48% reflector during winter solstice, from our estimation.

Photovoltaic panels have nonlinear characteristics. Therefore, there is only one point where the output power from photovoltaic panel at its maximum. This point is called the maximum power point (MPP). There are many of the maximum power point search algorithms in literature. The simplest methods are the open circuit voltage (OCV), the short circuit current (SCC), the perturb and observe method or the incremental conductance method. The most complicated methods use neutral networks or genetic algorithms. The maximum power point current depends on the short circuit current. However, to measure the short circuit current, the photovoltaic panel must be disconnected from the load. Some of methods use an additional module that represents the whole solar panel. The short circuit current depends on the solar irradiation mainly. Therefore, by the measurement of the irradiation the maximum power point current can be estimated. In this work the hybrid method that uses the solar irradiation measurement to determine the initial operating point and then the perturb and observe algorithm for the final seeking is used. The smaller initial seeking error, the smaller perturbation step of the perturb and observe method can be used and the seeking time is shorter. Therefore, in the testing algorithm the solar sensor is the critical element. In this article the linear and nonlinear light sensors in the short circuit current are tested. The integrated sensors like linear BH1603FVC, OPT3001IDNPRQ1, VEML6030 or nonlinear ISL29009 through phototransisors like TEPT4400, photodiode like BPW21 or photoresistor like GL5516 are compared.

Solar panels are devices that convert solar irradiation directly into the electrical power without any mechanical parts. The efficiency of solar cells is between 8-20% depending of manufacturer technology so it is important to use all available energy. On the voltage-current characteristics of the photovoltaic panel is a special point called the maximum power point. To find this special point special devices called the maximum power point trackers are used. If we connect each series of solar cells with bypass diodes to avoid the negative effect of the partial shading or the differences in the photovoltaic panel parameters, local maximum power points can appear. Therefore, the special algorithm that can track the real maximum power point must be used in the maximum power point tracker. In this work, the three-channel step down converter with the algorithm that uses the temperature and light measurement is designed and tested.

The alteration of graphene's electrical properties through chemical functionalization is a necessary process in order for graphene to fulfill its potential as a transparent conducting electrode. In this work, we present a method for the transfer and intercalation of large area (wafer scale) graphene samples to produce highly doped FeCl₃ intercalated Few Layer Graphene (FeCl₃-FLG). Given its excellent flexibility, transmission, and a sheet resistance, comparable to that of Indium Tin Oxide, FeCl₃-FLG has potential to replace alternative flexible transparent electrodes as well as compete with rigid transparent electrodes. We assess the effect of functionalization temperature on the degree of intercalation in the large area samples and comparing results to that of 1 cm² FeCl₃-FLG samples. Raman spectroscopy is then used to characterize samples, where we introduce a new figure of merit ({PosG}) by which to assess the degree of intercalation in a sample. This is an average G peak position, weighted by the areas of the constituent peaks, which can then be used to map the charge carrier concentration of the sample. The inhomogeneity of the graphene grown by chemical vapor deposition is found to be one of the limiting factors in producing large area, high quality FeCl₃-FLG.

In the work borate glasses with additives of copper and fluorine is considered. The luminescence quantum efficiency of these glasses reaches 50 % in the visible range. Therefore the concerned borate glass is the promising material for solar cell down-convertors, sensitive elements of the spark sensors and UV detectors and as a cheap phosphor for warm-white LEDs. All that makes boron glass doped with copper ions promising for use in devices such as spark sensors, down-converters, cheap phosphors for white leds.

The photoconversions efficiency of powerful collimated coherent single-mode and multimode wave beams with λ= 808 nm and 1064 nm was studied and the experimental results are presented. A set photocells based on silicon with different topological structure is considered including monofacial and bifacial cells, as well as those that have a vertical orientation. Photocell characteristics (short-circuit current I_sc, open-circuit voltage, V_oc and fillfactor) obtained in the temperature range from 25°C to 50°C and also at a beam power, P, of up to 100 Suns are discussed.

The article presents a methodology for analysis of power output the photovoltaic system depending on geometry of solar contractor mirrors. The concentrator directs the solar radiation reflected from mirrors onto photovoltaic surface, which increases the efficiency of solar panels. An essential element of the concentrator system is a two-axis tracking system which tracks the apparent position of the Sun on the celestial sphere. The analysis of luminance stream falling on photovoltaic surface depending on inclination angle of the concentrator mirrors made of electrochemically polished steel and resolution of step tracking system was performed. The technical light properties of the concentrator mirrors were determined using the BRDF function. The results of analysis were used to calculate the voltage, current and power output of photovoltaic system.