Spectrum Of Sun Research Articles

Modelling Various Solar Cells Materials Using Lorentzian-Drude Coefficients

In order to develop an optoelectronic model for simulating different light trapping structures sandwiching the photovoltaic active layer, determining the materials dispersion and absorption properties is a must. The targeted model should be able to simulate the desperation and absorption capabilities of different conductor and semiconductor materials over the entire sun spectrum (200 nm to 1700 nm). Therefore, the Lorentzian-Dude (LD) model is chosen due to its simplicity in implementation with the finite difference time domain algorithm chosen for optical modelling. In this paper, various materials are selected to be modelled with the LD model. The proposed algorithm is not only used for modelling material behaviour of various conducting materials published in literature, but is also used for other conducting and semiconducting materials that the original model was not capable of modelling over the entire range of spectrum. Besides that, the suggested algorithm showed a better time performance than those mentioned in literature. Experimental 1D grating structure prototype samples were made to validate the simulation results, showing perfect agreement.

New laboratory spectra of the Fe6+and Fe7+ions

The Fe6+ and Fe7+ ion spectra excited in a vacuum spark were recorded and investigated in the 120 - 350 A region. Previous identification is corrected and extended. A comparison with the Sun spectrum obtained from Hinode satellite was performed and identification of new lines was suggested.

Photoassisted Desulfurization Induced by Visible-Light Irradiation for the Production of Ultra-Low Sulfur Diesel Fuel Using Nanoparticles of CdO

The heterogeneous photocatalytic desulfurization processes have been paid wide attention due to their effectiveness in removing the condensed organo-sulfur compounds. Such methods may gain greater consideration via utilizing the visible light in general and sun spectrum in particular. This research work aims to produce low sulfur diesel fuel through a catalyzed photochemical route using nanoparticles of CdO under the visible-light irradiation. Two various structures of CdO were prepared in this study by both the chemical precipitation and autoignition techniques. The structural and morphological characteristics of the obtained cadmium oxides were determined via different tools of analyzes. The production of a low sulfur diesel fuel was then investigated under various operating parameters, such as type of light source, catalyst-to-feed dosage, and reaction time. The effect of adding oxidizing agents at different concentrations on the desulfurization process was also studied. After the maximum sulfur remova...

Metastability of a-SiOx:H thin films for c-Si surface passivation

The adoption of a-SiOx:H films obtained by PECVD in heterojunction solar cells is a key to further increase their efficiency, because of its transparency in the UV with respect to the commonly used a-Si:H. At the same time this layer must guarantee high surface passivation of the c-Si to be suitable in high efficiency solar cell manufacturing. On the other hand the application of amorphous materials like a-Si:H and SiNx on the cell frontside expose them to the mostly energetic part of the sun spectrum, leading to a metastability of their passivation properties. Moreover as for amorphous silicon, thermal annealing procedures are considered as valuable steps to enhance and stabilize thin film properties, when performed at opportune temperature. In this work we explored the reliability of a-SiOx:H thin film layers surface passivation on c-Si substrates under UV exposition, in combination with thermal annealing steps. Both p- and n-type doped c-Si substrates were considered. To understand the effect of UV light soaking we monitored the minority carriers lifetime and SiH and SiO bonding, by FTIR spectra, after different exposure times to light coming from a deuterium lamp, filtered to UV-A region, and focused on the sample to obtain a power density of 50μW/cm2. We found a certain lifetime decrease after UV light soaking in both p- and n-type c-Si passivated wafers according to a a-SiOx:H/c-Si/a-SiOx:H structure. The role of a thermal annealing, which usually enhances the as-deposited SiOx passivation properties, was furthermore considered. In particular we monitored the UV light soaking effect on c-Si wafers after a-SiOx:H coating by PECVD and after a thermal annealing treatment at 300°C for 30min, having selected these conditions on the basis of the study of the effect due to different temperatures and durations. We correlated the lifetime evolution and the metastability effect of thermal annealing to the a-SiOx:H/c-Si interface considering the evolution of hydrogen in the film revealed by FTIR spectra, and we developed a model for the effect of both treatments on the SiH bonding and the metastability shown in the lifetime of a-SiOx:H/c-Si/a-SiOx:H structure. We found that, after UV exposure, thermal annealing steps can be used as a tool for the c-Si passivation recovery and enhancement.

From Fluorine to Fluorene—A Route to Thermally Stable aza‐BODIPYs for Organic Solar Cell Application

Despite favorable absorption characteristics, borondipyrromethenes (BODIPYs) often lack thermal stability preventing their application in vacuum‐processed organic solar cells. In this paper, the replacement of the BF2 unit by borafluorene as a new functionalization strategy for this molecule class is explored. This approach is applied to a set of prototype molecules and demonstrates improved thermal stability, strong absorption in the red and near‐infrared region of the sun spectrum, as well as excellent solar cell performance. Synthesis is realized from free ligands via complexation with 9‐chloro‐9‐borafluorene giving high yields up to 81%. Planar heterojunction cells of these complexes exhibit high fill factors of more than 70%. Bulk heterojunction solar cells with C60 are optimized yielding power conversion efficiencies up to 4.5%, rendering the investigated prototype compounds highly competitive among other NIR‐absorbing small‐molecule donor materials. Comprehensive experimental material characterization and solar cell analysis are carried out, and the results are discussed together with simulations of molecular properties. Based on this analysis, additional performance improvements are proposed by engineering the intramolecular steric interactions towards further red‐shifted absorption.

The CU 2-D-MAX-DOAS instrument – Part 2: Raman scattering probability measurements and retrieval of aerosol optical properties

Abstract. The multiannual global mean of aerosol optical depth at 550 nm (AOD550) over land is ∼ 0.19, and that over oceans is ∼ 0.13. About 45 % of the Earth surface shows AOD550 smaller than 0.1. There is a need for measurement techniques that are optimized to measure aerosol optical properties under low AOD conditions. We present an inherently calibrated retrieval (i.e., no need for radiance calibration) to simultaneously measure AOD and the aerosol phase function parameter, g, based on measurements of azimuth distributions of the Raman scattering probability (RSP), the near-absolute rotational Raman scattering (RRS) intensity. We employ radiative transfer model simulations to show that for solar azimuth RSP measurements at solar elevation and solar zenith angle (SZA) smaller than 80°, RSP is insensitive to the vertical distribution of aerosols and maximally sensitive to changes in AOD and g under near-molecular scattering conditions. The University of Colorado two-dimensional Multi-AXis Differential Optical Absorption Spectroscopy (CU 2-D-MAX-DOAS) instrument was deployed as part of the Two Column Aerosol Project (TCAP) at Cape Cod, MA, during the summer of 2012 to measure direct sun spectra and RSP from scattered light spectra at solar relative azimuth angles (SRAAs) between 5 and 170°. During two case study days with (1) high aerosol load (17 July, 0.3 < AOD430 < 0.6) and (2) near-molecular scattering conditions (22 July, AOD430 < 0.13) we compare RSP-based retrievals of AOD430 and g with data from a co-located CIMEL sun photometer, Multi-Filter Rotating Shadowband Radiometer (MFRSR), and an airborne High Spectral Resolution Lidar (HSRL-2). The average difference (relative to DOAS) for AOD430 is +0.012 ± 0.023 (CIMEL), −0.012 ± 0.024 (MFRSR), −0.011 ± 0.014 (HSRL-2), and +0.023 ± 0.013 (CIMELAOD − MFRSRAOD) and yields the following expressions for correlations between different instruments: DOASAOD = −(0.019 ± 0.006) + (1.03 ± 0.02) × CIMELAOD (R2 = 0.98), DOASAOD = −(0.006 ± 0.005) + (1.08 ± 0.02) × MFRSRAOD (R2 = 0.98), and CIMELAOD = (0.013 ± 0.004) + (1.05 ± 0.01) × MFRSRAOD (R2 = 0.99). The average g measured by DOAS on both days was 0.66 ± 0.03, with a difference of 0.014 ± 0.05 compared to CIMEL. Active steps to minimize the error in the RSP help to reduce the uncertainty in retrievals of AOD and g. As AOD decreases and SZA increases, the RSP signal-to-noise ratio increases. At AOD430 ∼ 0.4 and 0.10 the absolute AOD errors are ∼ 0.014 and 0.003 at 70° SZA and 0.02 and 0.004 at 35° SZA. Inherently calibrated, precise AOD and g measurements are useful to better characterize the aerosol direct effect in urban polluted and remote pristine environments.

Understanding the role of mobility of ITO films for silicon heterojunction solar cell applications

Transparent conducting oxides (TCO) are crucial in amorphous/crystalline silicon heterojunction solar cells performance as they have to be highly conductive to ensure the transport of photogenerated charges while remaining highly transparent to the sun spectrum. The key parameter to improve the transparency/conductivity compromise of TCO is mobility, since it allows increasing conductivity without losing transparency in the infrared region. A deep understanding of the factors influencing the mobility is then fundamental, and this is the objective of this paper. For this study, thin films of tin-doped indium oxide (ITO) were prepared by magnetron sputtering with different oxygen content. They were deeply characterized by standard and Low Temperature Hall Effect measurement, scanning and transmission electron microscopy and X-ray diffraction. The impact of oxygen on the microstructure was studied and the electrical properties were deeply investigated. In particular, the different mechanisms impacting the mobility were quantified as a function of oxygen content during ITO deposition.

Ni2+ reduction under solar irradiation over CuFe2O4/TiO2 catalysts

The photo-electrochemical characterization of the hetero-system CoFe2O4/TiO2 was undertaken for the Ni2+ reduction under solar light. The spinel CoFe2O4 was prepared by nitrate route at 940 °C and the optical gap (1.66 eV) was well matched to the sun spectrum. The flat band potential (-0.21 VSCE) is more cathodic than the potential of Ni2+/Ni couple (-0.6 VSCE), thus leading to a feasible nickel photoreduction. TiO2 with a gap of 3.2 eV is used to mediate the electrons transfer. The reaction is achieved in batch configuration and is optimized with respect to Ni2+ concentration (30 ppm); a reduction percentage of 72% is obtained under sunlight, the Ni2+ reduction is strongly enhanced and follows a first order kinetic with a rate constant of 4.6×10-2 min-1 according to the Langmuir-Hinshelwood model.

Gains and Losses in PbS Quantum Dot Solar Cells with Submicron Periodic Grating Structures

Corrugated structures are integral to many types of photoelectronic devices, used essentially for the manipulation of optical energy inputs. Here, we have investigated the gains and losses incurred by this microscale geometrical change. We have employed nanostructured electrode gratings of 600 nm pitch in PbS colloidal quantum dot (PbS-CQD) solar cells and investigated their effect on photovoltaic properties. Solar cells employing grating structure achieved a 32% and 20% increase in short-circuit current density (Jsc) and power conversion efficiency, respectively, compared to nonstructured reference cells. The observed photocurrent increase of the structured devices mainly stems from the enhancement of photon absorption due to the trapping of optical energy by the grating structures. This optical absorption enhancement was particularly high in the near-infrared portion of the sun spectrum where PbS-based solar cells commonly present poor absorption. We have interestingly observed that the open-circuit vol...

Light-Induced EPR Spectroscopy of Charge Transfer in Low-Band-Gap PCDTBT:PC71BM Bulk Heterojunctions

The light-induced electron paramagnetic resonance (LEPR) study of spin charge carrier steady-state initiated by IR–Vis photons in an organic composite of a low-band-gap poly(N-9’-heptadecanyl-2, 7-carbazole-alt-5, 5-(4’, 7’-di-2-thienyl-2’, 1’, 3′-benzothiadiazole)) with a [6, 6]-phenyl-C 71-butyric acid methyl ester is reported. LEPR spectra of the composite were deconvoluted, and the main resonance parameters of polarons and anion radicals of methanofullerene were determined. The reversible formation in polymer backbone of spin traps, whose number, distribution, and depth is governed by the photon energy, has been shown. Part of the photoinduced charge carriers is pinned by such traps, resulting in the formation in the composite of polymer and fullerene domains with different band gaps and photon sensitivity. Relaxation and dynamics parameters of spin charge carriers were shown to depend on the energy of exciting photons. The mechanisms of polaron diffusion along and between polymer chains, as well as librations of methanofullerene cages in a polymer matrix, were proposed. Our results suggest that the use of C70-counterions as an electron accepter in the composite provokes its layered morphology. This hinders the formation of spin traps, increases the path length for charge carriers, and, therefore, accelerates their spin-assisted relaxation and dynamics through bulk heterojunctions within the visible and infrared regions of the sun spectrum with comparable effectiveness.

Tailoring high-temperature radiation and the resurrection of the incandescent source.

In solar cells, the mismatch between the Sun's emission spectrum and the cells' absorption profile limits the efficiency of such devices, while in incandescent light bulbs, most of the energy is lost as heat. One way to avoid the waste of a large fraction of the radiation emitted from hot objects is to tailor the thermal emission spectrum according to the desired application. This strategy has been successfully applied to photonic-crystal emitters at moderate temperatures, but is exceedingly difficult for hot emitters (>1,000 K). Here, we show that a plain incandescent tungsten filament (3,000 K) surrounded by a cold-side nanophotonic interference system optimized to reflect infrared light and transmit visible light for a wide range of angles could become a light source that reaches luminous efficiencies (∼40%) surpassing existing lighting technologies, and nearing a limit for lighting applications. We experimentally demonstrate a proof-of-principle incandescent emitter with efficiency approaching that of commercial fluorescent or light-emitting diode bulbs, but with exceptional reproduction of colours and scalable power. The ability to tailor the emission spectrum of high-temperature sources may find applications in thermophotovoltaic energy conversion and lighting.

Up-conversion luminescence from single vanadate through blackbody radiation harvesting broadband near-infrared photons for photovoltaic cells

Up-conversion (UC) is a promising route to harvest near-infrared (NIR) sunlight and enhance the power conversion efficiency (PCE) of photovoltaic (PV) cells. However, most of the UC materials have some bottleneck problems associated with them, such as own only narrower excitation band matching with the sun spectrum, lower UC luminescence efficiency, and considerable heat losses. Thus, it is essential to design and find a UC material that can absorb broadband NIR photons through an attractive route named thermal radiation for photon energy UC. In this work, we investigated the UC luminescence properties of single CeVO4 materials, in which the excitation bands can be augmented at least a range of 808–1064 nm. We also confirmed that this kind of UC emission is triggered by the thermal absorption of VO43−, which might be expanded to other single vanadate materials. The UC luminescence mechanisms were analyzed by power dependence and temperature modeling, and interpreted in terms of blackbody radiation theory. We demonstrated the possibility of photocurrent response in thin-film-hydrogenated amorphous silicon solar cell modified with CeVO4 powders through blackbody radiation for harvesting NIR photons. Such single vanadate materials can absorb broader NIR photons for UC luminescence through blackbody radiation, will open a new door for the enhancement of the PCE in the next-generation concentrated PV cells.

POLARIZED SCATTERING OF LIGHT FOR ARBITRARY MAGNETIC FIELDS WITH LEVEL-CROSSINGS FROM THE COMBINATION OF HYPERFINE AND FINE STRUCTURE SPLITTINGS

Interference between magnetic substates of the hyperfine structure states belonging to different fine structure states of the same term influences the polarization for some of the diagnostically important lines of the Sun's spectrum, like the sodium and lithium doublets. The polarization signatures of this combined interference contain information on the properties of the solar magnetic fields. Motivated by this, in the present paper, we study the problem of polarized scattering on a two-term atom with hyperfine structure by accounting for the partial redistribution in the photon frequencies arising due to the Doppler motions of the atoms. We consider the scattering atoms to be under the influence of a magnetic field of arbitrary strength and develop a formalism based on the Kramers--Heisenberg approach to calculate the scattering cross section for this process. We explore the rich polarization effects that arise from various level-crossings in the Paschen--Back regime in a single scattering case using the lithium atomic system as a concrete example that is relevant to the Sun.

Overcoming the Cut‐Off Charge Transfer Bandgaps at the PbS Quantum Dot Interface

Light harvesting from large size of semiconductor PbS quantum dots (QDs) with a bandgap of less than 1 eV is one of the greatest challenges precluding the development of PbS QD‐based solar cells because the interfacial charge transfer (CT) from such QDs to the most commonly used electron acceptor materials is very inefficient, if it occurs at all. Thus, an alternative electron‐accepting unit with a new driving force for CT is urgently needed to harvest the light from large‐sized PbS QDs. Here, a cationic porphyrin is utilized as a new electron acceptor unit with unique features that bring the donor–acceptor components into close molecular proximity, allowing ultrafast and efficient electron transfer for QDs of all sizes, as inferred from the drastic photoluminescence quenching and the ultrafast formation of the porphyrin anionic species. The time‐resolved results clearly demonstrate the possibility of modulating the electron transfer process between PbS QDs and porphyrin moieties not only by the size quantization effect but also by the interfacial electrostatic interaction between the positively charged porphyrin and the negatively charged QDs. This approach provides a new pathway for engineering QD‐based solar cells that make the best use of the diverse photons making up the Sun's broad irradiance spectrum.

Influence of morphology of low-band-gap PCDTBT:PC71BM composite on photoinduced charge transfer: LEPR spectroscopy study

Light-induced electron paramagnetic resonance (LEPR) study the steady-state of spin charge carriers initiated by Vis-NIR irradiation with the energy (wavelength) of 1.32–2.73eV (940–455nm) in organic composite of a low-band-gap poly(N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)) (PCDTBT) with a [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) within a wide temperature range is reported. LEPR spectra of the PCDTBT:PC71BM composite were deconvoluted and the main resonance parameters of polarons and anion radicals of methanofullerene were determined. The reversible formation of spin traps in polymer backbone, whose number, distribution and depth governed by the photon energy, has being shown. A part of photoinduced charge carriers is pinned by such traps resulting in formation of domains with different band gaps and photon sensitivity. Relaxation and dynamics parameters of all the charge carriers determined separately by the steady-state saturation method were shown to depend extremely on the energy of exciting photons. Polaron diffusion along polymer chains was analyzed in terms of spin interaction with the lattice phonons of crystalline domains embedded into amorphous polymer matrix. Activation of polaron hopping over the energetic barrier is characteristic for the charge transfer between polymer chains. Small-angle librations of methanofullerene cages in the polymer matrix were shown to follow the Markus model. Our results suggest that C70-counter-ions embedded into the PCDTBT backbone strengthen an overlapping of molecular orbitals and provoke a layered morphology of appropriate composite. This regularizes the polymer matrix, hinders the formation of spin traps and accelerates spin dynamics that in turn facilitates charge transport through bulk heterojunctions. It was shown that the spin-assisted photon-electron conversion is realized in the composite within the visible and near-infrared range of the sun spectrum with comparable efficiency.

First observation of helium in the Sun's spectrum

First observation of helium in the Sun's spectrum

Optimization of physico-chemical parameters for the photo-oxidation of neutral red on the spinel Co2SnO4

The spinel Co2SnO4 is prepared by chemical route to assess its feasibility for the oxidation of neutral red under visible illumination. The diffuse reflectance gives a band gap of 1.72 eV, properly matched to the sun spectrum. The electrons in the conduction band (0.16 VSCE), determined from the capacitance measurement, permit the formation of O2− radicals, responsible of the neutral red oxidation. The dye concentration, catalyst dose, agitation speed and light flux are optimized. A degradation of 85% is obtained under sunlight within 45 min for 10 mg/L concentration. The oxidation follows a pseudo second order kinetic with an apparent rate constant of 11.5 × 10−3 L/mg/min according to the Langmuir–Hinshelwood model.

The efficiency limit of CH3NH3PbI3 perovskite solar cells

With the consideration of photon recycling effect, the efficiency limit of methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells is predicted by a detailed balance model. To obtain convincing predictions, both AM 1.5 spectrum of Sun and experimentally measured complex refractive index of perovskite material are employed in the detailed balance model. The roles of light trapping and angular restriction in improving the maximal output power of thin-film perovskite solar cells are also clarified. The efficiency limit of perovskite cells (without the angular restriction) is about 31%, which approaches to Shockley-Queisser limit (33%) achievable by gallium arsenide (GaAs) cells. Moreover, the Shockley-Queisser limit could be reached with a 200 nm-thick perovskite solar cell, through integrating a wavelength-dependent angular-restriction design with a textured light-trapping structure. Additionally, the influence of the trap-assisted nonradiative recombination on the device efficiency is investigated. The work is fundamentally important to high-performance perovskite photovoltaics.

Smart photovoltaics based on dye-sensitized solar cells using photochromic spiropyran derivatives as photosensitizers

In this paper, smart photovoltaic (SPV) devices, integrating both functions of solar cells and smart windows, was fabricated based on dye-sensitized solar cells using photochromic spiropyran derivatives SIBT as photosensitizers. SPV devices have self-regulated power conversion efficiency (PCE) and light transmission responding to the incident spectra due to the photoisomerization of SIBT. SIBT isomerize from closed-ring form to open-ring form under UV illumination, accompanied with enhanced visible light absorption and electron delocalization. Therefore, increased PCE and absorption in SPV devices were observed under UV treatment and the devices can be restored gradually to the initial status when kept in dark. The SPV devices have self-regulation of PCE and sunlight transmission responding to the changing sun spectra in different times of a day, providing a proper energy usage and a better sun-shading.

Temporal Variation of Ca–K Line Profile of the Sun during the Solar Cycle 22 and 23

We obtained the Ca–K line profile of the Sun as a star since 1969 at the Kodaikanal Observatory (KO) and analysis of the data showed the need to delineate the role of different chromospheric features to the variations of solar irradiance. We, therefore, initiated a new methodology to make observations of Ca–K line profiles of the Sun as a function of latitude and integrated over the longitude on a daily basis since 1986. We have collected the data for about thousand days, spread over two solar cycles. Earlier data (before 1997) were recorded on the photographic film and later data using the CCD detector. The photographic film data were digitized and analysed along with the data obtained from CCD camera. From these data, we computed K1 and K2 widths for the Sun as a star, using all the observed line profiles as a function of latitude. In addition, we have analyzed the spectra of the whole Sun as a star obtained on some days and compared it with the results obtained from latitude spectra of the same day. The K1 and K2 widths of the Sun as a star derived from the KO data are compared with values determined from the observations made at other observatories to compare results from the new methodology of observations adopted by us and the earlier techniques. The average values of K1 width during the minimum period. of solar cycle 23 are smaller than those during the minimum period of cycle 22. Day-to-day variations in the K1 and K2 widths and plage areas may imply that irradiance variations occur not only due to large-scale solar activity, but also because of variations in some of the three types of network in quiet regions of the Sun. The variation in intensity of the plages can also cause day-to-day variations in widths.