Combined experimental and theoretical investigation of the hemi-squaraine/TiO2 interface for dye sensitized solar cells

Abstract

A simple hemi-squaraine dye (CT1) has been studied as a TiO2 sensitizer for application in dye sensitized solar cells (DSCs) by means of a combined experimental and theoretical investigation. This molecule is a prototype dye presenting an innovative anchoring group: the squaric acid moiety. Ab initio calculations based on Density Functional Theory (DFT) predict that this acid spontaneously deprotonates at the anatase (101) surface forming chemical bonds that are stronger than the ones formed by other linkers (e.g. cathecol and isonicotinic acid). Moreover an analysis of the electronic structure of the hybrid interface reveals the formation of a type II heterostructure ensuring adiabatic electron transfer from the molecule to the oxide. DSCs containing hemi-squaraine dyes were assembled, characterized and their performances compared to state of the art cells. Experimental results (large incident photon-to-electron conversion efficiency and an efficiency of 3.54%) confirmed the theoretical prediction that even a simple hemi-squaraine is an effective sensitizer for TiO2. Our study paves the way to the design of more efficient sensitizers based on a squaric acid linker and specifically engineered to absorb light in a larger part of the visible range.

Electrodes/Electrolyte Interfaces in the Presence of a Surface‐Modified Photopolymer Electrolyte: Application in Dye‐Sensitized Solar Cells

“…[19,34] In general, the increase of the lifetime is associated to a larger open circuit voltage. [35] In this case, nonetheless, the "PA side" cell exhibits lower V oc values: this is likely due to a downward shift of the TiO 2 conduction band, which counterbalances the effect of the larger lifetime. [36] On the other hand, this shift can contribute to the larger photocurrents measured for the "PA side cells".…”

TiO 2 nanotubes as flexible photoanode for back-illuminated dye-sensitized solar cells with hemi-squaraine organic dye and iodine-free transparent electrolyte

“…3a), that revealed a noticeable decrease in the 466 photocurrent of the quasi-solid cell. As it is known, howev- Moreover it has to be noted a red-shift of the IPCE spec-480 tra with respect to those presented in our previous works 481 [28,29]. Such shift is present in back-side illumination con-482 ditions [53] and has been ascribed to the fact that the long …”

“…Also nanotube carpets directly grown 96 by anodic oxidation on flexible metal foils have been sug-97 gested for a better transport of the photogenerated charges 98 [25,26]. In particular, our group has developed vertically 99 oriented not-curling free-standing TiO 2 NT membranes as 100 alternative photoanode material [27], hemi-squaraine 101 metal-free organic dye molecule (CT1) to be exploited in 102 substitution of the Ru-based N719 sensitizer [28][29][30], and 103 quasi-solid electrolytes such as UV-crosslinked polymer 104 membrane [31] and biopolymeric gels [32]. 105 It has however to be noted that despite the impressive 106 large number of research articles published on innovative 107 materials and concepts, the obtainable effects when they 108 are blended into a single device have been presented only 109 in few works [33][34][35][36].…”

“…Anodic oxidation 26 Hemi-squaraine dye 27 Iodine-free electrolyte 28 Polymer electrolyte 29 3 0 a b s t r a c t 31 Back-illuminated Dye-Sensitized Solar Cells (DSSCs) have been fabricated employing TiO 2 nan-32 otube (NT) arrays grown on a flexible Ti foil as a working electrode, an organic hemi-squaraine- 33 based dye (CT1) as sensitizer, and a iodine-free transparent redox mediator (both in liquid and 34 quasi-solid configuration) as electrolyte. The structural and morphological properties of the 35 photoanodes and the obtained electrical performances on the final DSSC devices reaching 36 conversion efficiencies values up to 2% have been presented and discussed.…”

A perspective on using experiment and theory to identify design principles in dye-sensitized solar cells

“…So while HfSQ dyes absorb at similar wavelengths to Ru-bipy dyes and so can act as potential replacements, squaraine dyes absorb where Ru-bipy dyes are less sensitive [40]. Half-squaraines have been tested in ZnO devices giving η = 0.27% [40] and 0.53% [41] and 3.54% [42] in TiO 2 devices. The synthetic versatility of HfSQs and squaraines has led to the publication of squaraines absorbing across the AM 1.5 solar spectrum, many of which efficiently harvesting light in the near infrared (NIR) [43–46].…”