Symmetric vs. asymmetric squaraines as photosensitisers in mesoscopic injection solar cells: a structure–property relationship study

Abstract

A symmetric squaraine and its related non-symmetric structure are shown to have comparable efficiencies in DSCs, but with undoubtedly advantages in the low cost and easiness of synthesis for the symmetrical structure.

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

“…In good agreement with the measured short-circuit current density, the IPCE spectra of the corresponding devices are reported in Figure 5b. The IPCEs of the non-substituted VG1 and VG10 are characterized by a broad and lower band in the blue region (S2) and a strong photo-conversion region between 550 and 750 nm (S1), with a maximum around 70%, according to [10,11]. Regardless of the structure, all the new four squaraines show an increased IPCE in the blue region (380-500 nm) and a noticeable decrease for S1 transition, together with a bathocromic shift.…”

“…J-V characteristics for VG2-C8, VG3-C8, VG11-C8, VG12-C8 sensitized solar cells measured under standard A.M. 1.5G illumination (100 mW/cm 2 ). The values are compared to the benchmark C106 ruthenium dye [2] and to VG1-C8 [10] and VG10-C8 [11] using the same electrolyte composition. In good agreement with the measured short-circuit current density, the IPCE spectra of the corresponding devices are reported in Figure 5b.…”

“…The first strategy implies the addition of a second anchoring group that provides a stronger electronic coupling with the semiconductor surface, a greater stability and a decrease in HOMO-LUMO energy levels contributing to a slight bathochromic shift of the spectral response of the sensitizer as in the case of VG1 dye [10]. The insertion of long alkyl chains, such as octyl on benzoindolenine moieties prevents the intramolecular rotation owing to the increased steric hindrance.…”

“…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].…”