A perylene bisimide tetraphenylethene derivative dispersed into different polymer matrices: tests of performances as luminescent solar concentrators (LSCs)

Optical solar concentrators concentrate light on small and highly efficient photovoltaic solar cells, thus lowering the cost of energy. Disadvantages are the need for rotation mechanisms to follow the Sun’s apparent motion, and of a cooling system to disperse the excess heat due to unconverted energy. To compensate for these defects luminescent solar concentrators (LSCs) were developed [1]. In LSCs, an inert polymer contains a dye which converts part of the absorbed radiation into a longer emitting wavelength by fluorescence. The red-emitted light is concentrated via total internal reflection in the optical waveguide construction. Therefore, solar cells attached to LSC can generate more electric power than conventionally used ones. Organic dyes are non-toxic species whose optical properties can be optimised so to improve their efficiency for uses in LSCs [2]. We report on the characterization of an organic fluorophore [3] containing the perylene bisimide (PBI) core connected to tetraphenylethene units (1,7-DTPEPBI, Figure 1 left), and on its use in LSCs. The optical properties in solution were evaluated in different solvents and solvent/non-solvent mixtures, evidencing aggregation-induced emission (AIE). 1,7- DTPEPBI maximum of excitation is peaked around 375 nm, with maximum emission at around 635 nm. The large Stokes’ shift (260 nm) ensure the minimisation of auto-absorption phenomena. The dye is then casted in different polymer matrices: poly(methyl methacrylate) (PMMA), poly(cyclohexyl methacrylate) (PCHMA), a P(CHMA-co-MMA 20:80) copolymer and poly(vinyl butyral) (PVB). They all were tested as for quantum yield, compatibility, auto-absorption phenomena and optical efficiencies at different wt.%. On the whole, the less polar PVB ensures a better homogeneity of the films with respect to PMMA ones. PCHMA and P(CHMA-co-MMA 20:80) produce rigid and fragile films. Also, in PVB the emission band is 35 nm blue-shifted with respect to PMMA. These data show that PVB may be a good matrix for PBI dyes. Preliminary tests on the optical efficiency (ηopt%) yield that ηopt% = 12% ca. for 1,7-DTPEPBI (Figure 1 right). Further tests are needed to confirm these performances, however, tetraphenylethene/PBI molecules seem to be a promising class of organic dyes to be further analysed as LSCs.