A luminescent solar concentrator (LSC) is a clear piece of glass or plastic that has fluorescent dye or quantum dots embedded in it or painted on it. The dye absorbs incident light then fluoresces creating a glow that spreads by total internal reflection to the sheet’s edge where light can be absorbed by a narrow solar cell. LSC is a really promising technology as it enables a large collecting area made of nearly transparent glass with a relatively small area of expensive solar cells. The concentration factor can be defined as the ratio of the aperture to the edge. The luminescent materials can be tuned for absorption at certain wavelengths (as an example ultraviolet UV) and re-emit at longer wavelengths that are optimal for absorption by silicon.
Design of luminescent solar concentrator cells
Initial designs of LSC typically included parallel flat, thin layers of interchanging luminescent and transparent materials, positioned to collect incoming radiation on their boarder and emit concentrated radiation around their narrow edges. Normally, the device would direct the concentrated radiation onto the surface of solar cells to generate electrical energy.
Concentration factor of luminescent solar concentrator cells
Most devices (like solar cells) for converting the incoming energy to other useful output are comparatively small in size and costly, and their optimum operation is to convert directional light at high intensity and frequency range which is narrow, while input radiation tends to be at diffuse frequencies, which has fairly low saturation and irradiance. Therefore, concentration of the input energy is considered one good option for efficiency and economy.
This leads to a really important point which is the difference between the concentration factor and efficiency of luminescent solar concentrator cells. The concentration factor is defined as the ratio between the incoming and emitted irradiance while the efficiency is defined as the ratio between the incoming radiant flux (watts) and the outgoing wattage.
Definition of Luminescence and its relevance to luminescent solar concentrator cells
The vital characteristic of LSCs is that they include luminescent materials which have the ability to absorb incoming light with a wide frequency range, and then energy is re-emitted by luminescent materials in the form of light in a narrower frequency range. The narrower the frequency range, (which also means the higher the saturation) the simpler a PV cell can be designed to convert this light range into electricity.