Increased efficiency of luminescent solar concentrators after application of organic wavelength selective mirrors

Abstract

Organic wavelength-selective mirrors are used to reduce the loss of emitted photons through the surface of a luminescent solar concentrator (LSC). A theoretical calculation suggests that application of a 400 nm broad reflector on top of an LSC containing BASF Lumogen Red 305 as a luminophore can reflect 91% of all surface emitted photons back into the device. Used in this way, such broad reflectors could increase the edgeemission efficiency of the LSC by up to 66%. Similarly, 175 nm broad reflectors could increase efficiency up to 45%. Measurements demonstrate more limited effectiveness and dependency on the peak absorbance of the LSC. At higher absorbance, the increased number of internal re-absorption events reduces the effectiveness of the reflectors, leading to a maximum increase in LSC efficiency of ~5% for an LSC with a peak absorbance of 1. Reducing re-absorption by reducing dye concentration or the coverage of the luminophore coating results in an increase in LSC efficiency of up to 30% and 27%, respectively.

Special dispersion chiral nematic reflectors for luminescent solar concentrators

“…We previously calculated the potential increase in the efficiency of an LSC assuming no re-absorption events by addition of a cholesteric reflector [16]. The fluorophore used in these earlier LSC studies was Lumogen Red305 [17], a perylene-based dye with a high fluorescence quantum yield [18] and good photostability [19].…”

“…The fluorophore used in these earlier LSC studies was Lumogen Red305 [17], a perylene-based dye with a high fluorescence quantum yield [18] and good photostability [19]. and 400 nm to be maximally 51%, 65% and 91% [16]. The assumption of isotropic emission is a simplification: we have calculated that emissions from dichroic dyes, even isotropic systems, can result in non-uniform emission profiles [20,21].…”

“…Our previous work focused on determining the performance of LSCs using narrow and broadband cholesterics exposed to direct sunlight normal to the surface of the lightguide [8,16].…”

“…The extraordinary refractive index (black dotted) is constant with wavelength, while the ordinary refractive index changes. The dispersion is varied by changing parameter BJ: please refer toTable III.The reflective properties of the cholesteric phase formed by these materials are calculated according to the method described in[10,16,25,26] for 75 run, 175 run and 400 run broad reflectors with an onset wavelength of 620 run, 620 run and 650 run, respectively An example of calculated angular dependent reflective properties from a 400 run broad reflector is depicted inFig. 2.The difference in reflective properties between the special dispersion cholesteric (SDC) reflectors with the same wavelength of zero birefringence, using different dispersion parameters is relatively small.…”

Angle-resolved photoluminescence spectrum of a uniform phosphor layer

“…Probability of trapping light has been modeled for both isotropic emission and electric dipole emission. 36 The use of optical means such as wavelength-selective mirrors 37 and Bragg reflectors 38 has been proposed for enhancing trapping efficiency.…”