Effect of Alkyl Chain Length on the Sensitizing Action of Substituted Non‐Symmetric Squaraines for p‐Type Dye‐Sensitized Solar Cells

Abstract

The design and the synthesis of three unsymmetrical squaraines, DS_34, DS_45, and DS_47, have been achieved for their utilization as sensitizers of screen‐printed NiO cathodes in p‐type dye‐sensitized solar cells (p‐DSCs). DS_34, DS_45, and DS_47 are bidentate dyes, each bearing two carboxylic anchoring groups, which differ solely in the length of alkyl chain attached to the nitrogen atom of the condensed pyrrole ring (ethyl, butyl, and dodecyl for DS_45, DS_34, and DS_47, respectively). The photoelectrochemical properties of the corresponding p‐DSCs are compared and analyzed in terms of the structural differences of DS_34, DS_45, and DS_47. The benchmark dye, p‐SQ2, has also been employed as a p‐DSC sensitizer for the sake of comparison. Current density−voltage (JV) curves and incident photon‐to‐current conversion efficiency (IPCE) spectra revealed the major efficaciousness of the DS_45 as a dye‐sensitizer, as it was the only system that produced a p‐DSC surpassing 0.04 % of overall efficiency (η). This finding was attributed mainly to the larger surface concentration of chemisorbed DS_45 with respect to the other squaraines.

Influence of the Conditions of Sensitization on the Characteristics ofp-DSCs Sensitized with Asymmetric Squaraines

“…Dye CDCA:dye molar ratio Table 2). In the absence of the co-sensitizer, the most performing squaraine is DS_45 in accordance to previously 283 reported results [41]. The external quantum efficiency determined at the condition of short-circuit presents spectral profiles The IPCE (incident photon-to-current conversion efficiency) spectra are characterized by the presence of two different see table 2).…”

“…As far as the observation in point (d) is 438 concerned, i.e. the scarce dependence of the chemical capacitance C µ on the concentration of CDCA in the solution of 439 sensitization, the lack of a univocal trend in the chemical capacitance C µ upon variation in the CDCA concentration in the 440 sensitizing solution (Table 3) is consistent with the fact that the chemical capacitance is mostly affected by the nature of the 441 electrode material itself rather than the nature of the chemisorbed species [41]. In fact, the variation in the concentration of 442 CDCA in the solution of sensitization affects the amount of CDCA chemisorbed onto the NiO electrode surface but not the 443 chemical capacitance C µ of the electrode itself.…”

Effect of Sensitization on the Electrochemical Properties of Nanostructured NiO

“…For the quantitative determination of dye loading in the case of the NiO sample sensitized with Fast Green (FG), the desorption method could not be adopted because of the scarce effect of dye desorption with the ordinary bleaching agents having medium basic strength. Within the family of DS squaraines, all three members possess the same extent of electronic conjugation but differ in the length of the alkyl chain [44]. Because the difference (OCV dark (NiO) − OCV dark (NiO-DS)) increases from DS_44 (230 mV) to DS_46 (275 mV), with DS_35 displaying the intermediate value (240 mV), we evince that DS_46, with its longer substituent (dodecyl group) and the lowest surface concentration (0.35 × 10 −8 mol cm 2 ), is the sensitizer with the strongest ability to passivate the surface charge of NiO among the three symmetric squaraines of the DS family.…”

“…The optical [10][11][12][13][14]30,31], magnetic [32,33], electrochemical [34], and photoelectrochemical [35,36] properties of NiO (either in the bulk state or in the nanostructured version) are considerably altered when the surface of the oxide is dye-sensitized [37]. Such a type of electrode modification consists mainly in the impartation of additional optical absorption [38][39][40][41][42][43][44][45][46][47][48][49] and photoelectroactivity to NiO in the NIR-Vis range, i.e., in a spectral range of lower energies with 2 of 18 respect to the intrinsic optical absorption of pristine NiO (typically in the near ultraviolet (UV)) [50]. Dye sensitization of nanostructured p-type NiO is finalized principally to the realization of devices, such as dye-sensitized solar cells of p-type (p-DSCs) [51][52][53][54][55][56][57][58][59], light-fueled electrolyzers for hydrogen generation [5,[60][61][62][63][64][65], and photoelectrochemical reactors for carbon dioxide reduction …”

Effect of Sodium Hydroxide Pretreatment of NiOx Cathodes on the Performance of Squaraine‐Sensitized p‐Type Dye‐Sensitized Solar Cells

“…The high number of carboylic groups in the symmetrical structures (O4, CN4), as well as the cis‐conformation forced by the presence of dicyanovinyl‐substituted squaric core (CN2, CN4), allowed better charge injection and recombination. To further explore the electron transfer directionality in the unsymmetrical structures, the chain‐length on the indolenine nitrogen was varied in the series ,…”