Highly Efficient Luminescent Solar Concentrators Based on Benzoheterodiazole Dyes with Large Stokes Shifts

Abstract

Five extended π‐conjugated systems with electron donor (D) and acceptor (A) moieties have been synthesized. Their basic D‐A‐D structural motif is a benzothiadiazole unit symmetrically equipped with two thiophene rings (S2T). Its variants include 1) the same molecular framework in which sulfur is replaced by selenium (Se2T), also with four thiophene units (Se4T) and 2) a D’‐D‐A‐D system having a N‐carbazole donor moiety at one end (CS2T) and a D’‐D‐A‐D‐A’ array with a further acceptor carbonyl unit at the other extremity (CS2TCHO). The goal is taking advantage of the intense luminescence and large Stokes shifts of the five molecules for use in luminescent solar concentrators (LSCs). All of them exhibit intense absorption spectra in the UV/Vis region down to 630 nm, which are fully rationalized by DFT. Emission properties have been studied in CH2Cl2 (298 and 77 K) as well as in PMMA and PDMS matrices, measuring photoluminescence quantum yields (up to 98 %) and other key optical parameters. The dye–PMMA systems show performances comparable to the present state‐of‐the‐art, in terms of optical and external quantum efficiencies (OQE=47.6 % and EQE=31.3 %, respectively) and flux gain (F=10.3), with geometric gain close to 90. LSC devices have been fabricated and tested in which the five emitters are embedded in PDMS and their wave‐guided VIS luminescence feeds crystalline silicon solar cells.

Benzothiadiazole vs. iso-Benzothiadiazole: Synthesis, Electrochemical and Optical Properties of D–A–D Conjugated Molecules Based on Them

“…The patterns of changes in the EO values of BTD- and isoBTD-based compounds with substitution of substituents conform to the general rules. In the series with furan ( 3b ), thiophene ( 3a ) and selenophene ( 3c ) the oxygen-containing analogue 3b has one of the lowest oxidation potential values, which may be due to the reduced aromatization energy [ 38 ] of the furan ring. The addition of strong donor substituents (EDOT 3e , 4e and CPDT 3f , 4f ) leads to a significant decrease in the EO potential compared to compounds with five-membered heterocyclic substituents ( 3a – c , 4a – c ), both in the series BTD and in the series isoBTD derivatives.…”

Polymer/dye blends: Preparation and optical performance: A short review

“…These results show the effect of BCB concentration on the optical properties of PMMA/BCB blends. In the second study, Gao et al 46 investigated CS2TCHO dye–doped PMMA films with different dye concentrations (0.2, 0.5, and 1.0 wt%), prepared from dichloromethane solution. The maxima in the emission spectra of the films shift to longer wavelengths with increasing dye concentration, due to re‐absorption effects.…”

Review of the Fundamental Principles and Performances on Lminescent Solar Concentrators

“…In 2019, two PDIbased organic light-emitting molecules with different bandgaps were used to induce the Förster resonance energy transfer (FRET) phenomenon, enabling the fabrication of a large-area LSC with a high Stokes shift [10]. Elsewhere, increasing the Stokes shift has been demonstrated by synthesizing an organic light-emitting material based on a D-A-D (donor-acceptor-donor) structure [11]. Additionally, combining perovskite nanocrystals and organic light-emitting molecules has been shown to increase the Stokes shift via FRET [12].…”