Different photonic light trapping structures realized by a combination of interference- and nanoimprint-lithography as well as based on self-organization processes are presented. Their potential as rear side light trapping structures for silicon based tandem solar cells is evaluated based on the comparison of EQE measurements and optical modeling. The photonic structure used in the current world record III-V silicon tandem solar cell is a metallic crossed grating with 1μm period. This structure is shown in detail and acts as benchmark for the comparison of the concepts. Finally, the requirements for a successful implementation of photonic structures in highest efficiency solar cells are shown.

In this paper, we present findings on micro-concentrator photovoltaic cells composed of lattice matched subcells grown on GaAs and InP substrates, which are stacked into single, four-terminal devices using micro-transfer printing. The design, modeling, growth, fabrication and assembly of the devices will be described, and potential interconnection schemes to achieve efficient, two-terminal strings of cells with flexible current and voltage outputs and resilience to defects is discussed.

We propose to explore tandem junctions associating single crystalline silicon bottom cell (bandgap of 1.12 eV) and CIGS top cell (bandgap of 1.7 eV), and using wide bandgap GaP intermediate layers. Our purpose is to grow CIGS films under epitaxial conditions on GaP to improve the CIGS top cell efficiency, thanks to a reduction of the structural defects density detrimental for the cell performance, so that CIGS-Si tandem solar cells can emerge as cost competitive for the next generation of PV modules. Epitaxy of CIGS on GaP/Si platform is demonstrated and preliminary results on CIGS cell on GaP/Si is reported.

We use ensemble Monte Carlo simulation of electrons and holes to investigate ultrafast carrier processes related to hot carrier capture and multi-exciton generation relevant for advanced photovoltaic devices. The particle based simulation includes electron-phonon scattering in quantum wells and quantum wires, intercarrier scattering including impact ionization, and nonequilibrium phonon effects. For quantum well devices, we elucidate how nonequilibrium phonons and real/k-space transfer contribute to the slower energy relaxation rates observed in quantum well structures. For nanowires, we show that energy relaxation is slowed due to bandstructure effects and reduced dimensionality, and that impact ionization is enhanced above the threshold, leading to strong carrier multiplication.

A hot-carrier solar cell (HCSC) is a high-efficiency photovoltaic concept where electrons and holes are at a higher temperature than the lattice, allowing an additional thermoelectric energy conversion. There are two requirements for a HCSC: establishing a hot-carrier population and converting the temperature into extra voltage through energy-selective contacts. We focus on the generation of hot carriers, and the design of absorbers that can make this generation easier. Fundamentally, this requires to increase the power density absorbed per volume unit, so the photocarriers cannot fully thermalize (phonon bottleneck). Beyond simply increasing the light intensity, the main control knobs to favor hot carriers include reducing the thickness of the absorber, increasing its absorptivity, and reducing its bandgap. In this proceeding, we report the fabrication of structures that aim at measuring the influence of these different parameters. We justify our choices for sample structure and fabrication method from the need for high thermal conductivity, in order to prevent lattice heating. We characterize our structures in order to determine precisely the final thickness of all layers, and the absorptivity of the absorber layer. These samples are to be used for an analysis of the temperature with many variable parameters, in order to better understand the thermalization mechanisms and design better absorbers. Ultimately, our objective is to implement all solutions together in order to evidence a hot carrier population under concentrated sunlight illumination.

Hot-carrier effects on the photocurrent generation in quantum well solar cells are assessed on the basis of quantum transport simulations under simultaneous consideration of electron-photon, electron-phonon, and electron-electron scattering. The interactions are treated on equal footing via respective self-energy expressions in the non-equilibrium Green‘s function formalism. Under moderate light concentration, carrier-carrier scattering preserves the electronic structure, but enhances the escape rate of carriers generated in confined states due to the creation of a hot carrier quasi-equilibrium population above the barrier. Both elevated carrier temperature and fast carrier escape are reflected in the simulated photoluminescence spectra, in agreement with experimental observation.

Photoluminescence spectroscopy is a powerful technique to investigate the properties of photo-generated hot carriers in materials in steady state conditions. Hot carrier temperature can be determined via fitting the emitted PL spectrum with the generalized Planck’s law. However, this analysis is not trivial, especially for nanostructured materials, such as quantum wells, with a modified density of states due to quantum confinement effects. Here, we present comprehensively different methods to determine carrier temperature via fitting the emitted PL spectrum with the generalized Planck’s law and discuss under what conditions it is possible to simplify the analysis.

We present a comprehensive approach to the characterization and modeling of photovoltaic metal-halide perovskite single junction devices and perovskite-silicon tandem solar cells. The framework is based on 1D opto-electronic device simulation in steady-state and transient modes as well as frequency domain including specific features of the perovskite materials such as mobile ions, combined with a broad variety of device characterization experiments. As a salient feature, advanced optimization algorithms are used for reliable parameter extraction and opto-electronic device optimization purposes in both single junction and tandem solar cell architectures.

4-terminal tandem solar cells with an efficiency of 21.7% was synthesized and modelled, combining a semitransparent perovskite solar cell (PSC) as top cell with an efficiency of 16.6% and a commercially-available Aluminium Back Surface Field (Al-BSF) silicon bottom cell. In order to further improve the efficiency of the tandem solar cell, the parasitic optical losses in the PSC have to be minimized, mostly in the near infrared region (NIR), in order to optimize the efficiency of the silicon cell. The modelling of the optical path into the PSC was obtained with the transfer matrix method in order to identify precisely the losses and to optimize the tandem cells. Two interfaces with the air appear critical to decrease parasitic reflection, and the TCO layers and the substrate are mainly responsible for absorption in the NIR. A first optimization allow to improve the efficiency at 23.2% by replace the soda-lime glass, using an anti-reflection coating on the glass-air interface and a interlayer between the silicon and the perovskite cell. A second improvement concerns the two FTO and ITO electrodes, and show that a reduction of their absorption by 10 allow to reach 23.7% (+2%). Finally, the simulated tandem cell reaches 25.5% (+3.8%) when all the improvements are combined. Thus, this work aims to quickly test the interest of various materials, by the prediction of the optical properties of the PSC and their impact on the efficiency of the bottom silicon cell and in consequently the complete tandem cell.

Hybrid perovskites have emerged as exceptional semiconductors for optoelectronic applications. Here, we control the cation alloying to push optoelectronic performance through alteration of the charge carrier dynamics in mixed-halide perovskites. In contrast to single-halide perovskites, we find high luminescence yields for photo-excited carrier densities far below solar illumination conditions. Using time-resolved spectroscopy we show that the charge-carrier recombination regime changes from second to first order within the first tens of nanoseconds after excitation. Supported by microscale-mapping of the optical bandgap and elemental composition, electrically-gated transport measurements and first-principles calculations, we demonstrate that spatially-varying energetic disorder in the electronic states causes local charge accumulation, creating p- and n-type photo-doped regions, which unearths a strategy for efficient light emission at low charge-injection in solar cells and LEDs.

Internal quantum efficiency (IQE) is a key parameter determining solar cell power conversion efficiency. While reported IQEs of metal-halide perovskite solar cells are often close to one, the contributions of photoluminescence reabsorption (PLr) and surface recombination (SR) to IQE has not been elucidated. In this work, both effects are examined by photoluminescence spectroscopies and time-resolved terahertz spectroscopy (TRTS). Then PLr rate and SR velocity are extracted from TRTS kinetics by diffusion theory. At last a model is proposed to calculate the carrier-collection probability and discuss contributions of PLr and SR on the IQE.

I will lay out the general role of interfaces halide perovskite based solar cells, as I will discuss the impact of the interface formation on device performance, considering effects such as chemical reactions and surface passivation on interface energetics and stability. The focus of the talk will be on the characterization of the surface properties of the perovskite absorber films and their interfaces to adjacent charge transport films by photoemission spectroscopy and complementary optical and X-ray spectroscopies. We use this set of techniques to track potential degradation pathways as well as the energy level alignment at these interfaces, and to determine the impact on the optoelectronic properties of the perovskite absorber films.

High absorption coefficient, suitable band gap, and high electron mobility makes non-toxic 2D bismuth iodide (BiI₃) a promising alternative to efficient, toxic perovskites and inorganic solar cells containing lead (Pb). In this work, we successfully synthesized, controlled, and optimized the crystal orientation of BiI₃ crystals grown directly on a transparent conductive substrate using a custom-built close space sublimation (CSS) method. Morphology characterization by scanning electron microscopy (SEM) confirms the controlled morphology of BiI₃ crystals. Record photoexcited carrier lifetime of 0.6 ns was characterized by time-resolved photoluminescence spectroscopy for the optimized vertical BiI₃ crystals. The photoluminescence confirmed the band gap of the BiI₃ film to be 1.82 ev which is a suitable band gap for photovoltaic application. The optimized vertical BiI₃ crystals device showed a power conversion efficiency of 0.6% due to the fact that the optimized vertically oriented crystals allowed us to harness the high in-plane electron mobility of BiI₃. Higher efficiencies can be obtained by further optimizing the electron and hole transport layers in our PV device. This work paves the way for controlling the orientation and morphology of BiI₃ for efficient solar cells by using a facile, scalable, and transfer-free CSS method.

Non-contacting optical probes based on spectroscopic ellipsometry or reflectance measurements are used to predict photovoltaic (PV) device performance and to diagnose optical and electronic losses. Optical modeling of aluminum back surface field (Al-BSF) silicon, thin film cadmium telluride (CdTe), and hybrid organic inorganic lead halide based perovskite (FA_1−xCs_xPbI₃) solar cell technologies are reviewed. Using the near infrared (IR) to ultraviolet (UV) optical properties of PV device component materials and the device structures as input, external quantum efficiency (EQE) spectra are simulated for Al-BSF, CdTe, and perovskite solar cells for comparison with experimental EQE and short circuit current density (J_SC). Optical Hall effect measurements of Al-BSF PV determine majority and minority carrier transport properties in the n+ emitter and p-type wafer silicon; from this information open circuit voltage (V_OC), fill factor (FF), J_SC, and power conversion efficiency (PCE) are calculated and agree well with direct current-voltage (J-V) electrical measurement. An IR-extended optical model for Al-BSF silicon PV includes coherent multiple reflections, ray tracing optics, and diffuse scattering and is applicable as a baseline for developing optical and thermal management strategies. Analysis of EQE for CdTe based solar cells with selenium alloying (CdSe_1−yTe_y) enables determination of absorber composition after full device processing. EQE modeling for perovskite solar cells includes the ability to account for sub gap absorption measured in films but not present in the solar cell absorber and incomplete photogenerated carrier collection in the PV device.

This paper describes a study of perimeter recombination on millimeter-scale multijunction photovoltaic cells using luminescence characterizations and a quasi-3D PV modeling. Device performance of controlled GaAs 1J cells shows an obvious perimeter dependency. By contrast, the performance of controlled InGaP 1J cells is less dependent on perimeters. Corresponding InGaP/GaAs 2J cells are assessed whose results exhibit combined contributions from both subcells. Luminescence method using current transport efficiency mapping and the PV modeling are able to reveal the influence of perimeter recombination and series resistance effect for individual subcells.

Over the last several decades, champion photovoltaic (PV) devices using CuInGaSe2 (CIGS) as the absorber material have been achieved using polycrystalline films exclusively. This has led to the assumption that polycrystalline CIGS generally outperform single-crystal CIGS in PV devices. However, recently, very high-quality epitaxial CIGS has been grown on GaAs substrates producing PV device efficiencies of 20.0%. These results have revived the debate on what effects grain boundaries have on PV device efficiencies. In this contribution, we compare the optoelectronic properties of polycrystalline CIGS films with those of high-efficiency epitaxial CIGS films. This comparison reveals that grain boundaries are associated with properties that negatively impact PV device efficiency. Additionally, we find that the grain interiors in polycrystalline films exhibit properties that are similar to the high-performance epitaxial films. Our results suggest that it may be possible to achieve higher device efficiencies with epitaxial CIGS than with polycrystalline films.

Electron beam induced current (EBIC) was applied in the study of dye sensitized solar cell (DSSC), which present properties such as electrical stability, the possibility to use curved geometries, and cost-effectiveness. In the studied cells, the liquid electrolyte was replaced by a solid-state hole transport material (HTM) based on spiro-OMeTAD solution. Since the irradiation of electrons in a solar cell produces electron-hole pairs in a similar way as the photon irradiation, the EBIC measurements allowed the evaluation of the conductivity between FTO and electrolyte containing TiO₂, the current homogeneity in the active layer, the EBIC signal behavior as a function of cell thickness, and the differences observed in the collection of electron and holes in each contact, leading to the mapping of the charge carrier generation and collection efficiency in the cross section of the DSSC. The combination of EBIC, grazing incidence X-ray diffraction (GIXRD) and Energy dispersive spectrometry (EDS/SDD) were used to demonstrate the homogeneity of the generated electrical current, phase and composition distribution in the studied cells. The enhancement in the electrical conduction between the contact layer (FTO) and the photoanode after treatment with TiCl₄ was demonstrated. Our work demonstrates that EBIC can be used as an important support quality control technique of solid-state dye sensitized solar cells, indicating the need of efficiency improvement in regions like the interface between FTO/TiO₂ and depth distribution of HTM into the cell.

Strained InGaAs (In = 8%) quantum wells (QW) were inserted into the intrinsic region of n-i-p InGaP/GaAs heterojunction solar cells, with thin (1 nm to 4nm) GaAs barriers separating the QWs. This design exhibited improved carrier collection from the QWs as compared to thicker barrier designs, as well as almost no degradation in Voc from control devices without QWs. Champion devices incorporating three layers of strained InGaAs QWs exhibited conversion efficiencies of >26%, exceeding that of the control, with corresponding short circuit current of 30.22 mA/cm2 and open circuit voltage of 1.03V under 1-sun AM1.5G solar spectrum.

Solar cells based on multiple quantum wells have attracted a great deal of attention in recent years. Due to the superior radiative nature, the output voltage is expected to be more ideal over solar cells made of bulk materials. In this research, based on the effective map analysis technique we proposed previously to ensure a fair comparison, we investigate quantum well solar cells and their bulk counterpart in terms of radiative efficiency, and compare several significant properties at a consistent absorption edge wavelength. This provides a good insight into the factors which limit the efficiency of quantum well solar cells.

Transport and charge separation are crucial steps in molecular or hybrid energy converters. We have developed a theoretical-numerical framework within the nonequilibrium Green’s function formalism to investigate the time-dependent transport of charges and energy, including the Coulomb interaction in the Hartree-Fock approximation. We thus analyze charge transport and separation in a donor-acceptor nanojunction illuminated with a femtosecond laser pulse. Our analysis conducts us to depart from the standard view of static density of states and driving energy, and to rather define and handle dynamical quantities on which relying to design ultrafast optoelectronics and highly efficient photovoltaics.

Nanostructures play an important role in state-of-the-art photovoltaic devices. Optical and electrical characteristics of the devices can be improved with properly designed and fabricated nanotextures. In this contribution, we highlight examples of possible fabrication of nanotextures by using UV nanoimprinted lithography, their optical characterization by camera based angular resolved spectroscopy and perform computer-assisted design of nanotextures for best optical performance of heterojunction silicon and ultra-thin chalcopyrite solar cells.

Ultra-thin (< 100 nm absorber thickness) GaAs cells are a promising avenue for the design of solar cells with increased radiation tolerance for space applications. To address the high transmission loss through such thin absorber layers, rigorous coupled-wave analysis and a semi-analytical waveguide model are used to investigate the effectiveness of silver/dielectric hexagonal grating structures placed on the back of a thin (86 nm) GaAs cell. The grating is formed of silver disks in a dielectric (SiN_χ), and simulations indicate an optimum period of 600-700 nm with a grating thickness around 100 nm. Using the results of external quantum efficiency and light current-voltage measurements of thin devices without light-trapping features, predicted efficiencies for cells with a grating structure are found to be up to double that of the cells without light-trapping designs, showing a significant potential for current enhancement through light-trapping.

Silicon solar cells benefit from an internal Lambertian light distribution achieved through texturing, while the performance of direct-bandgap materials can be lower with an internal Lambertian light distribution than the light distribution of a planar cell. A novel analytic expression is derived for the emittance of cells with a Lambertian light distribution and partial rear reflectance. This expression enables comparison of Si, GaAs, CdTe, and CIS cells under planar and Lambertian light distributions with varying rear reflectance in the Auger limit. A Lambertian light distribution is shown to be particularly beneficial to thinner material with higher rear reflectance due to absorptance enhancement. It is found that a Lambertian light distribution increases radiative recombination in most absorbers but can reduce radiative recombination in some CIS material.

Bifacial photovoltaics present a clean and cheaper alternative to diesel generators for high-latitude remote communities; however, solar cells are typically tested at 0° angle of incidence, 25°C, and AM1.5, from which high-latitude conditions vary greatly. A bifacial silicon photovoltaic cell optimized for high-latitude conditions will improve energy yield for these systems. We integrate experimentally-derived cell parameters with a systems-level model capable of fixed-tilt and tracked energy yield predictions. We optimize to find the most efficient cell design for high-latitude environments in Sentaurus and SunSolve and determine the resulting improvement in energy yield for an entire panel in MATLAB.

In intermediate band solar cells (IBSCs), voltage preservation is a key issue to overcome efficiency limit in singlejunction solar cells. To achieve this, quasi-Fermi level splitting of respective transitions should be investigated because equivalent circuit model of an IBSC is series-parallel connected diodes. In this study, we have quantitatively investigated quasi-Fermi level splitting, Δμ in InAs quantum dot solar cells (QDSCs) by performing absolute intensity calibrated photoluminescence (PL) spectroscopy. Multi-stacked InAs/GaAs QDs were fabricated in the i-region of a GaAs p-i-n single-junction solar cell. QD ground states and GaAs band edge emissions were observed simultaneously by using a near-infrared sensitive CCD spectrometer. Excitation density dependence and temperature dependence were investigated in detail to clarify photo-carrier kinetics in QDSCs and tackle the voltage preservation issue on IBSCs. At room temperature, nonlinear increase in PL intensity was clearly observed at high excitation density above 1000 suns. Absolute PL spectra was analyzed at respective transitions by using generalized Plank’s law. As the result of detail analysis, increase in Δμ was confirmed at high excitation density and at room temperature, which suggested voltage recovering via photo-filling effect. It would be desirable to implement voltage preservation in IBSCs.

This theoretical study sheds light on questions raised by inter-subband transition in quantum dot intermediate band solar cells. Based on a dedicated analytical model that correctly treats, from a quantum point-of-view, the trade-off between the absorption, the recombination and the electronic transport, we clearly show that it is essential to control the transit rate between the excited state of the quantum dot and the embedding semiconductor with a tunnel barrier. Such a barrier, matching the recombination and the tunnel rates, allows to strongly improve the current. On the other hand, by better controlling the retrapping, such a barrier can also improve the voltage. Finally this work, by giving a framework to design efficient inter-subband transitions, opens new opportunities for quantum dot intermediate-band solar cells.

We identified the factors that limit the conversion efficiency of narrow bandgap thermophotovoltaic (TPV) cells and investigated how these factors affect key performance aspects such as quantum efficiency (QE), fill factor and open-circuit voltage. Calculations are made for narrow bandgap InAs/GaSb superlattice materials to elucidate how the conversion efficiency is limited by these factors for specific material parameters such as the product of absorption coefficient a and diffusion length L. It is shown that the multi-stage interband cascade (IC) structure is able to solve the problem of low QE in single-absorber TPV cells, therefore, increase conversion efficiency by about 10% in a wide range of aL. Also, the dependence of conversion efficiency on the illumination source is investigated, which shows the flexibility and advantage of multi-stage IC structure to achieve its maximum efficiency with the incident photon energy near the bandgap.

One of the problems of energy harvesting with nanoantennas is a limited coherence length of solar or any other greybody radiation. In our previous paper on the subject, we proposed using Talbot effect to enhance, potentially indefinitely, the coherence length of blackbody radiation. Current paper extends this result by providing a theory, which takes into account a finite aperture of incipient beam. In this context we must mention that for monochromatic laser beam, the transmission through a correctly placed second grating completely restores coherence, smeared by the first grating. Because of an extended spectral range of blackbody radiation, complete reconstruction of an image obtained by metamaterial propagation is not possible and additional structures appear in a beam. We try to demonstrate extra features of blackbody radiation, which appear on propagation through the periodic structures located at average Talbot distance for the emission spectrum of the source.

Previous publications suggest that geometrical solar panels are more efficient in terms of using the mounting space than traditional flat static solar panels. However, previous research does not deeply discuss the questions of the distribution of solar cells on the considered segments of cylinders, cones, spheres, and catenoids. To find the best geometry, we optimize the parameters of various curved surfaces, such as cones and catenoids, for the greatest energy produced per square meter. In practice, these curved solar panels are created by packing flexible fixed size square solar cells onto the curved surface. So, we must also optimize our curved surfaces for their ability to be packed efficiently with square solar cells. Using combinatorial methods, we propose sample solar cells packing and approximate energy production to optimize geometrical solar panels at various geographic locations. These techniques allow us to create more efficient static solar panels and improve the overall value of solar energy.

The motivation behind this research lies in the well-spread news about USA and China’s plans to build bases on the moon within the next 10 years. In this research, we create a mathematical model of efficiency for geometrical solar panels, as well as discuss which locations on the moon may be suitable for placing a non-tracing solar power plant. We consider the North Pole, the Equator and additional locations; and analyze the accumulation of illumination over an 18.6-year period that represents the lunar cycle. The simulation for geometrical panels is based on the etendue, with the panel being the diaphragm and a selected segment of the sky being the source. However, the etendue needs to be modified due to the properties of solar energy. The selected segment of the sky is crafted with careful analysis of the motion of the moon. The difficulty of the model comes from the fact that the motion of the sun on the moon’s sky is subject to change in its speed and direction, which is created by the moon’s libration. In addition, we discuss the change of luminosity of the sun’s light due to the varied distance between the moon and the sun. The simulation was performed using MATLAB and Mathematica.

Photovoltaic (PV) cells are the most efficient devices when absorbing photons with energies similar to its bandgap energy. They are therefore incapable of harvesting sub-bandgap photons in the infrared regime and experience significant thermalization losses when absorbing photons in the visible regime with energies above that of the bandgap energy. This excess heat from both regimes has a detrimental effect on the PV cell’s efficiency and lifetime due to the temperature rise. This dilemma has highlighted the need for a photovoltaic device able to utilize the excess heat generated effectively. In this work, an integrated hybrid photo-thermo-voltaic system is presented. The system is comprised of a plasmonic enhanced silicon PV cell with a nanostructure surface to increase the absorption of the visible spectrum. The cell is attached to a heavily doped silicon-based plasmonic infrared super absorber to trap the thermal/infrared portion of the spectrum, facilitating the harvesting of sub-bandgap photons and excess heat from the thermalization losses. The PV and absorber layers of the solar system can be easily fabricated with low cost due to their CMOS compatibility. This harvested heat energy is then utilized to heat the hot side of a connected thermo-electric generator (TEG), which directly convert waste energy into electric power by creating a temperature gradient across the TEG. This TEGs based on traditional semiconductor material 𝐵𝐵𝑖𝑖2𝑇𝑇𝑒𝑒3. Radiation energy near the bandgap is directly transformed to electricity by PV panel and simultaneously, infrared energy is utilized by the TEG to convert heat to electricity. Consequently, more electricity can be produced by the hybrid system than the power produced by a single PV or TE system. The system exhibits a considerable improvement in efficiency and power output when compared to a standalone PV cell or TEG owing to the utilization of the lost heat and IR solar spectrum. Promising applications of the system include energy storage and solar heating.

Nanostructuring for the purpose of reflectance reduction has been widely investigated for Silicon based solar applications. Bare Silicon surfaces reflect between 50 and 60 % of the incident light and are thus unsuitable for absorbing significant amounts of sunlight. A typical approach to addressing this is to use an anti-reflective coating on top of the Silicon which reduces reflectance via destructive interference. Since this interference is mainly dependent on the thickness of film this type of anti-reflection layer can only be optimized for a certain wavelength and thus is inherently limited. To reduce the reflectance over a broad range of wavelengths a structuring based approach is necessary. A common approach to implementing this is by wet etching the top surface of a crystalline solar cell to create pyramid structures based on the crystalline dependence of the etching process. Since this approach exploits the crystalline structure it is most suited for crystalline Si. Dry etching based nanostructuring can offer a high level of control over the resulting structure with the crystalline dependence being less concern. One approach is to etch cylindrical holes arranged in a periodic fashion into the top surface of the device to create a photonic crystal lattice. Here we present a systematic analysis of a photonic crystal slabs in Silicon and how the geometry affect the reflectance of the device. Lumerical’s FDTD solution is used to vary the pitch, diameter and depth of the cylindrical holes making up the Photonic Crystal structure. The analysis reveals that air fill fraction and hole depth are the most significant determinants of the overall reflectance.

The thermoelectric effect can be defined as the power that can be ascribed to the results of the temperature gradient across a junction between two different metals. Micro thermoelectric generators (μTEGs) are used with energies or losses that have a gradient in temperature or spatial dimensions that are too small for conventional thermodynamic heat engines to effectively utilize, delivering micro-Watts to milli-Watts of power per device. Silicon nanowires (SiNW) thermoelectrical properties are more enhanced compared to thin-layer silicon, mainly due to the decrease of thermal conductivity caused by the quantum confinement and phonon scattering effects in low dimensions. SiNWs as a thermoelectric material is also very advantageous due to the abundance of silicon as raw material and its ability to be produced by regular IC manufacturing techniques leading to low cost. Here, our present works show a portable and autonomous power generation microsystem based on a SiNWs μTEG coupled with an infrared plasmonic absorber for heat-trapping purposes capable of powering micro/nano system. One of the major sources of harvesting energy for the μTEGs is the human skin which is presented in our work. The μTEG is integrated with a micro silicon-based plasmonic IR absorber plate in order to harvest thermal energy in the IR regime. This enhanced μTEG/absorber hybrid exhibited an increased ability to trap minimum excess heat on its surface owing to the IR absorber, resulting in a considerable enhancement in output power and conversion efficiency when compared to a standard μTEG. In this work, full simulations of the absorber are performed in addition to electrical and thermal simulations for the μTEG by using COMSOL Multiphysics Simulator. The integrated hybrid microsystem is easily fabricated using standard CMOS processes and has many applications, such as the powering of wireless sensors and the harvesting of lost heat from electronic components.

Due to the high cost of conventional crystalline silicon solar cells, researchers have been attracted towards the development of thin-film Si solar cells, where a several hundred nanometers thick amorphous Si (a-Si) or microcrystalline Si (μc-Si) solar cell layer is deposited by plasma-enhanced chemical vapor deposition (PECVD). This paper presents the use of plasmonic nanostructures in μc-Si p-i-n junction thin-film solar cells to increase the absorption in a broad spectral range. Finite-difference time-domain (FDTD) simulation results demonstrate a broadband absorption enhancement in these solar cells due to plasmonic nanostructures. The enhancement in the absorption is attributed to the enhanced electromagnetic fields in the active layer due to the excitation of surface plasmon modes and photonic Bloch modes at multiple wavelengths. Moreover, the plasmonic nanostructures lead to a significant enhancement in the shortcircuit current density of the μc-Si thin-film solar cell.