High-efficiency and ultrathin crystalline silicon solar cells (SCs) with a frequency upconversion (UC) layer and an array of silver nanohemispheres were presented. The light-trapping performances of SCs embedded with different volume ratios and radii of Ag nanohemispheres were systematically studied by finite-element analysis. The simulation results show that the short-circuit current density of the SCs and the light-field intensity in the UC layer can be significantly improved by adjusting the structural parameters of Ag nanohemispheres. The short-circuit current density of the structured SCs have been improved by 16.48% and the light-field intensity in the UC layer has been increased by 2.65 times compared to that of planar SCs. Additionally, the UC effects on the power conversion efficiency of the SCs were also investigated. The presented model will serve as the basis for further preparations of high-efficiency ultrathin crystalline SCs.
When a satellite sensor with a large field of view and wide swath is calibrated, it is not easy to obtain the image when the calibration site is located precisely at the nadir position. If the location of a calibration site is at an off-nadir position in the image, calibration errors will be caused by the inconsistent observation angle between the sensor view and the ground measurement view. The bidirectional reflectance distribution function (BRDF) model plays an important role in solving this problem. In this study, a BRDF measurement system based on an unmanned aerial vehicle (UAV) is developed. This system has the capability of measuring angular data with observation azimuth angle ranging from 0 deg to 360 deg with an angle interval of 30 deg, and observation zenith angle ranging from 0 deg to 50 deg with an angle interval of 10 deg. The directional data of the Dunhuang calibration site were measured using the UAV BRDF measuring system at different solar zenith and azimuth angles, and the spatiotemporal distribution characteristic of forward- and backward-scattering of Dunhuang calibration site was analyzed. A Ross–Li BRDF model, built using measurement data, is used to calculate the directional surface reflectance under any observation geometry of solar and satellite. These calculations are applied to correct the calibration data of the CBERS-04 WFI sensor. Results show that the BRDF model significantly improves the calibration accuracy, especially in the case of large observation angles.
The optical trap of thin-film silicon solar cells is very important for improving efficiency and reducing cost. A composite nanostructure with front silicon nanocone gratings and rear Ag nanohemisphere gratings is proposed. The relationship between the geometrical parameters of the hybrid nanostructures and the optical properties of the silicon solar cells was studied using the finite element method. The light-harvesting ability was studied systematically using COMSOL Multiphysics. The simulation results show that the optimum parameters of the front silicon nanocone grating are a diameter of 350 nm, height of 250 nm, and pitch/diameter ratio of 1.1. The optimum parameters of the rear Ag hemispherical grating are a diameter of 270 nm and pitch/diameter ratio of 1.4. The average absorption of the hybrid nanostructure solar cell is 78.5%, and the short-circuit current density is 36.6 mA/cm2, representing an enhancement of 171.1% compared with that (13.5 mA/cm2) of the reference cell.
KEYWORDS: Solar cells, Absorption, Silicon, Nanostructures, Crystals, Reflection, Optical spheres, Titanium dioxide, Finite element methods, Solar energy
Ultrathin-crystalline-silicon solar cell is important for its low cost and flexibility, but its efficiency is low. Light trapping technology is a useful way to improve the efficiency. In this paper, we design a TiO2 nanosphere arrays on the top of the ultrathin-crystalline-silicon solar cells with 2-μm-thickness to achieve advanced light trapping property. The finite element method is used to study the optical properties of the sphere nanostructure on the ultrathin-crystalline-silicon solar cells. The light trapping ability is systematically studied by COMSOL multiphysics. The results show that the sphere nanostructure can highly increase the light absorption of the ultrathin-crystalline-silicon in the wavelengths from 300 to 1200 nm. The average absorption rate increases by 58.63% compared to 2-μm-thick crystalline silicon.
Light trapping in thin-film solar cells is important for improving efficiency and reducing cost. We propose a hybrid nanostructure based on the anodic aluminum oxide grating and Si3N4 double-layer antireflection coatings combined with Ag nanoparticles to achieve advanced light trapping property in gallium arsenide (GaAs) solar cells with 500-nm thickness. The finite-element method is used to study the relationship between geometrical parameters of hybrid nanostructure and optical characteristics of thin-film GaAs solar cells. The light trapping ability is systematically studied by COMSOL multiphysics. The simulation results show that the hybrid nanostructure can highly increase the light absorption in the wavelengths from 300 to 860 nm. The average absorption in 500-nm-thick GaAs layer is 96.7%. The short circuit current density in 500-nm-thick GaAs layer is 30.2 mA/cm2, representing a 58.9% enhancement compared with that (19.0 mA/cm2) of the reference cell. Research paves the way for designing highly efficient light trapping structures in thin-film GaAs solar cells.
A series of Zr(1 mol%):Cu(0.1 mol%):Fe(0.03wt%)LiNbO3 single crystals with various Li/Nb ratios having compositions varying between 48.6 and 58 mol% Li2O in the melt were grown by the Czochralski method in the air. The OH− transmittance spectra was investigated to characterize the structure defects of these crystals. The OH− absorption peaks shift to longer wavelength as the [Li]/[Nb] ratio increases and an obvious absorption peak at 3468 cm-1 was observed at the Li/Nb ratio of 1.05. The photorefractive properties of the crystals were experimentally studied using the two-wave coupling method. The results show that as the [Li]/[Nb] ratio increases, the holographic response time and the diffraction efficiency increase under the Li/Nb ratio of 1.2.
The congruent Zr:Ce:Fe:LiNbO3 crystals have been grown by the Czochralski method with fixed concentrations of CeO2 and Fe2O3 and various concentrations of ZrO2. The Ultraviolet(UV)-Visible(Vis) absorption spectra were measured in order to investigate their defect structures and their optical damage resistance was characterized by the transmission light spot distortion method. The results show that the optical damage resistance of the Zr:Ce:Fe:LiNbO3 crystals improves with the doping concentration of ZrO2 increasing. The dependence of the optical damage resistance on the defect structure of Zr:Ce:Fe:LiNbO3 crystals was discussed.
In:Tm:LiNbO3 crystals were grown by the Czochralski technique with fixed concentrations of Tm2O3 and differing
concentrations of In2O3. Their ultraviolet-visible absorption spectra were measured in order to investigate their defect
structures and their optical damage resistance was characterized by the transmission light spot distortion method. The
results show that the optical damage resistance of the In:Tm:LiNbO3 crystals improves with the doping concentration of
In2O3 increasing. The dependence of the optical damage resistance on the defect structure of In:Tm:LiNbO3 crystals is
discussed in detail.
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