The reabsorbing effect will prevent the receiving energy for the solar cell attached to the edge of a luminescent solar concentrator from increasing with the illuminated area. The conventional solar concentrator adopts a uniform luminescent layer made of only one type of phosphor or dye. When the light generated in the region of the luminescent layer far away from the solar cell propagates to the solar cell by multiple total internal reflections, it will have more chances to be reabsorbed when it enters the region of the luminescent layer near to the solar cell. We investigate how the reabsorption effect can be reduced by using a luminescent layer made of multiple phosphors such that the region with the phosphor absorbing the longer wavelength is arranged to cover the region nearer to the solar cell. Experimental results show that the proper coverage with multiple phosphors can reduce the reabsorption effect in our luminescent solar concentrator under test.
As an application of the PV technology, building integrated photovoltaic (BIPV) technologies have attracted an increasing interest in the past decade. One of these BIPV elements is the luminescent solar concentrators (LSCs). The LSC consists of a transparent plate embedded with luminescent dyes or inorganic particles, and the solar cells are attached on one or more sides. The incoming sunlight absorbed by the luminescent dyes or inorganic particles re-emits at a longer wavelength, and part of the re-emitting light trapped in the transparent plate reaches the PV cell attached on the LSC and convert it to electricity. However, the efficiency of the LSCs is still low at this stage. The surface loss on the top surface of the transparent plate is one of the main losses in LSCs. The prism film in liquid-crystal display (LCD) module is used to collimate the light in the module and enhance the overall brightness, and would be used in the LSCs to enhance the incoming sunlight to the solar cells attached on the end of the transparent plate. Then the design of the prism film is important. In this study, the ray-tracing simulation is used to investigate the optical characteristics of the LSC with the prism film covered on the top surface of the transparent plate. Different structure of the prism film will be considered to enhance the light reaches the PV cell attached on the LSC.
Effects of a coating combination, a prism film and a phosphor layer on the short current of the solar cell in the optical solar concentrator and the illuminance of the sunlight passing through the samples were investigated. The optical solar concentrator was a 50 mm x 50 mm x 5 mm B270 thick glass with its sides connected by a solar cell. The prismatic structure of the prism film had a period of 50 μm. A phosphor Y560 having an absorption band of 390 nm to 500 nm and emitting from 490 nm to 700 nm was prepared. Six coating combinations applied in this study were composed of optical filters and glass. The optical filters included infrared cut-off, magenta, red, green and blue filters. The deflection angle was between 31 and 33 degrees when the incident sunlight passed through the prism film. The short current of the solar cell in the optical solar concentrator with the prism film, the coating combination and the phosphor layer was largest in this study. Experimental results show that the coating is more suitable for enhancing the short current than the phosphor layer in the optical solar concentrator with the prism film. And the phosphor layer can increase the illuminance of the sunlight passing through the samples due to the human eye sensitivity.
We present a method for enhancing the light conversion efficiency of a luminescent solar concentrator by putting a prism film on the upper surface for receiving the incoming light. The luminescent solar concentrator under study was composed of a thick glass with a luminescent film deposited on the top surface and a solar cell attached to the lateral surface. The prism film will deflect the incident light into two different directions. Dependence of the conversion efficiency on the incident angle of the sunlight and influence of the rotation of the prism film on the conversion efficiency were also investigated. Experimental results show that the prism film will increase the light falling on the solar cell in our luminescent solar concentrator.
In this paper, the luminescent solar concentrator comprises a thick glass with a spectrally-selective optical coating deposited on the bottom surface and an inorganic phosphor layer contacted on the coating surface. A solar cell is contacted to the lateral surface of the thick glass. Spectrally-selective coatings are applied to reflect and redirect the invisible solar radiation to the edges of luminescent solar concentrators. These coatings also transmit the visible solar light and the emission light of the inorganic phosphor. The short-circuit current of the solar cell is measured in a flashing-mode solar simulator with metal-dielectric heat mirrors and dielectric edge filters coated on the thick glass of the luminescent solar concentrators respectively. Experimental results show that the dielectric edge filter will increase the short-circuit current of the solar cell and the invisible light falling on the solar cell in our luminescent solar concentrator. The metal-dielectric coatings, silver-based transparent heat mirrors, will not increase the short-circuit current of the solar cell in our luminescent solar concentrator due to absorption of metal films.
By using a light-emitting diode as the probing light source and a Shack-Hartmann wave-front sensor to execute a relative measurement, we present a simple and sensitive method for measuring surface fluctuation of a nominally flat sample. We used an epitaxial wafer for test. The reflected wave front from the surface of the sample was first calibrated to be a planar surface. The surface fluctuation of the test sample could be estimated from the increment on the variance of the wave-front surface to its regression plane after the sample had been shifted by a small distance by using the Bienaymé formula.
Conventionally, it is a tedious work to measure the beam quality factor for a laser beam because one needs to move a camera-based beam profiler from one location to another for many times to record intensity profiles at different positions around the beam waist. We present a simple method for determining the laser beam quality factor from only two laser intensity profiles at different cross sections around the waist. We first used an iterative phase-retrieval algorithm, based on the Huygens-Fresnel principle, to reconstruct the phase profiles at the two cross sections where the intensity profiles had been measured. Once the optical field amplitude (the square root of intensity) and phase distribution functions at certain cross section of a laser beam had been determined, we can propagate the light wave at this cross section by using the Fresnel diffraction formula to obtain the intensity profiles at different positions, from which the beam quality factor can be determined. Using a HeNe laser for test, we had experimentally demonstrated the feasibility of our idea by showing that the result from our proposed method is in good agreement with that obtained from the conventional method. Our setup is capable of executing a real-time measurement of the beam quality factor because the two intensity profiles can be simultaneously recorded by using a beam splitter and two beam-profilers controlled by the same computer.