Panchromatic symmetrical squaraines: a step forward in the molecular engineering of low cost blue-greenish sensitizers for dye-sensitized solar cells

Abstract

Two novel symmetrical blue squaraine sensitizers were synthesized, which exhibit panchromatic light harvesting and a record efficiency over 6% with Jsc exceeding 14 mA cm(-2), and Voc over 620 mV under 1 sun. Their color, low cost, easiness of synthesis, and relatively high photo- and thermal stability open up the way for commercial applications.

Dicyanovinyl and Cyano-Ester Benzoindolenine Squaraine Dyes: The Effect of the Central Functionalization on Dye-Sensitized Solar Cell Performance

“…The measured HOMO levels are positive enough to have energetically favorable dye regeneration by iodide species (−0.28 V) [11]. On the other hand, the LUMO levels of VG2, VG3, VG11 and VG12 dyes are −1.51, −1.59, −1.55 and −1.63 V (vs. Fc/Fc + ), respectively.…”

“…Vertical transitions energies of the four molecules are reported in Table S4 (see Supplementary Materials). We point out that whereas the dyes can certainly exist in different configurations, previous computational analyses on squaraines suggest that different isomers have very similar electronic spectra [11,22]. The predicted first excitation energies are about VG2, VG3, VG11 and VG12 dyes exhibited the first oxidation potentials at 0.26, 0.15, 0.16, and 0.06 V (vs. Fc/Fc + ), respectively.…”

“…This was demonstrated by NMR analysis showing the presence of more than one conformer in solution on the timescale of the experiment. As a result, 6.1% power conversion efficiency was obtained for VG10-C8 dye [11]. Interestingly, the modification of the squaric core, first proposed by Beverina et al, appears as a promising alternative strategy to lock the structure into the cis-configuration [12].…”

“…Then, thanks to our previous results with VG1-C8 [10] and VG10-C8 [11] dyes, we also prepared two new benzo-derivative analogs VG11-C8 and VG12-C8. Actually, VG2-C8 and VG11-C8 have a strong electron-withdrawing dicyanovinyl group on the squaric acid core while VG3-C8 and VG12-C8 bear a cyano-butyl-ester substituent.…”

“…It occurs through a twisted intramolecular charge transfer (TICT) process that yields a non-radiative decay of the dye excited state, hampering quantitative fast electron injection and consequently limiting the cell efficiency [9]. Different strategies were proposed to block the photoisomerization mechanism in these structures: the doubling of anchoring moieties, the insertion of long alkyl chains on the lateral groups or the functionalization of the squaric core unit [10][11][12].…”