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Phosphors for Environmentally Friendly Technology
Published in Vijay B. Pawade, Sanjay J. Dhoble, Phosphors for Energy Saving and Conversion Technology, 2018
Vijay B. Pawade, Sanjay J. Dhoble
In general, PV does not have the ability to use all incident light for energy generation cells; only a small portion of the solar spectrum, corresponding to some of the UV-visible or near infrared (NIR) range is used for electricity, and part of the solar light is wasted due to a spectral mismatch between the incident light and the solar cell plate. To avoid the spectral mismatch and to minimize other losses that affect the efficiency of the cell, some new ideas have been introduced to enhance the efficiency of existing solar cells by using an upconversion or downconversion phosphor as an active layer by coating it onto the solar plate; their properties have already been discussed in Chapter 3. Another concept reported for enhancing the efficiency is the use of a luminescent solar concentrator (LSC). An LSC is a device for concentrating radiation, solar radiation in particular, to produce electricity. It operates on the principle of collecting radiation over a large area, converting it by luminescence and directing the generated radiation into a relatively small output target. In the case of light guide–based solar concentrator systems, the incident light is coupled to a plate and then guided toward small photovoltaic cells on the basis of the phenomenon of total internal reflection (TIR). Such devices are attractive, inexpensive, and thin and can also be easily integrated into appliances.
Polymer dispersed liquid crystal device with integrated luminescent solar concentrator
Published in Liquid Crystals, 2018
Fahad Mateen, Heemuk Oh, Wansu Jung, Sae Youn Lee, Hirotsugu Kikuchi, Sung-Kyu Hong
The importance of energy-saving technologies is recently increasing in order to mitigate the effects of global warming and to overcome the energy crisis caused by the increasing prices of fossil fuels. A huge energy-saving potential lies in building sector, as the buildings are responsible for one-fifth of the world’s total energy consumption [1]. In line with the worldwide efforts, employment of ‘smart windows’ is of prime importance as they have a capability to control the throughput of thermal and solar radiations depending on the dynamic needs; consequently, helps to reduce artificial lighting-, cooling- and heating-related energy consumptions. An additional attractive feature of such windows includes a provision of indoor comfort along with improved decoration effects [2]. Generally, a smart window is regarded as a window that changes its transparency in response to the external signals. The technologies available for smart windows are commonly characterised by the materials that are used. At present, three different materials (chromic materials, polymer dispersed liquid crystals (PDLC) and suspended particles) have been reported for the fabrication of smart window [3]. Among these candidates, PDLC device owns the advantage of fast switching speed, better transparency and high durability and thus provides substantial benefits to the end users [4]. A working mechanism of a typical PDLC device is based on the reorientation of liquid crystal (LC) molecules between two conductive electrodes by applying an electric field, resulting in a transmittance modulation [3,5,6]. Moreover, provision of self-powering feature to PDLC window is an important consideration for achieving nearly zero energy consumption in buildings. This could be done by combing PDLC window with photovoltaic-active elements. Luminescent Solar Concentrator (LSC), on the other hand, is currently being considered a potential complement to integrate photovoltaic devices into built environment [7–10]. A standard LSC device comprises of transparent material (glass or polymer) embedded in or coated with a luminophore. Light is absorbed by the luminophore and is re-emitted at a longer wavelength. A portion of the emitted light is trapped by total internal reflection (TIR) and concentrated at the device edges wherein a solar cell can be attached for conversion of light into electricity [11–13]. Important aspect of LSC device is its capability to harvesting direct, diffused and ground-reflected light; therefore, the measurable amount of energy can be generated even in non-ideal illumination conditions [14,15]. Previously, fewer reports have been presented regarding the combination of LSC-based PDLC windows [16,17]. However, their focus was to explore the light harvesting through embedding a luminophore in the same PDLC device. Usually, in such configurations, absorption of luminophore decrease drastically owing to their homeotropic alignment on applying the voltage as the dipole moment of dye and the electric field vector of the incoming light are close to orthogonal to each other [16,18].