Abstract
Most organic dyes synthesized for dye-sensitized solar cells (DSC) use a single linker group to bind to the metal oxide photo-anode. Here we describe the synthesis and testing of two new triphenylamine dyes containing either two carboxylic acids 5-[2-(4-diphenylamino-phenyl)-vinyl]-isophthalic acid (10) or two cyanoacrylic acids (2Z, 2′Z)-3, 3′-(5-((E)-4-(diphenylamino) styryl)-1, 3-phenylene) bis (2-cyanoacrylic acid) (8) as linker groups. Full characterization data are reported for these dyes and their synthetic intermediates. DSC devices have been prepared from these new dyes either by passive or fast dyeing and the dyes have also been tested in co-sensitized DSC devices leading to a PCE (η = 5.4%) for the double cyanoacrylate linker dye (8) co-sensitized with D149. The dye:TiO2 surface interactions and dye excitations are interpreted using three modelling methods: density functional theory (at 0 K); molecular dynamics (at 298 K); time dependent density functional theory. The modelling results show the preferred orientation of both dyes on an anatase (1 0 1) TiO2 surface to be horizontal, and both the simulated and experimental absorption spectra of the dye molecules indicate a red shifted band for (8) compared to (10). This is in line with broader light harvesting and Jsc for (8) compared to (10).
Highlights
O’Regan and Grätzel’s breakthrough paper in dye-sensitized solar cells (DSC) used theRu-bipyridyl dye (N3) adsorbed on a mesoporous TiO2 photoanode leading to a power conversion efficiency (PCE) of 7.2% [1]
From our atomistic simulations we infer that in experimental devices, both dyes adsorb to the surface in horizontal orientations, which might change with an increase in dye concentration, i.e., if space becomes limited for horizontal, mono-layer dye packing, the molecules might be forced to pack closer together in more vertical than horizontal orientations
The atomistic modelling work carried out using density functional theory, time dependent density functional theory, and molecular dynamics provides a deeper level of insight to the experimental work, with the proviso that the models are simplifications of the experimental systems and as such are subject to limitations, notwithstanding which the intention is to capture the essential interactions prevalent in
Summary
O’Regan and Grätzel’s breakthrough paper in dye-sensitized solar cells (DSC) used the. We report the synthesis of two new triarylamine dyes with double linker groups for adsorption onto TiO2 photo-anodes These new dyes have been fully characterized (including single crystal X-ray crystallography) and have been tested in DSC devices leading to power conversion efficiencies of 1.2% for the double carboxylate dye (10) and 2.4% for the double cyanoacrylate linker dye (8). Ultra-fast co-sensitization has been examined for these dyes which consistently shows improved light harvesting (i.e., higher Jsc ) and PCE with the highest efficiency achieved for a combination of (8). We have previously applied this to single linker triphenylamine dyes structurally related to dyes (8) and (10) reported here [19] Whilst this technique provides useful information about the electronic behavior of DSC devices, it does not study dye:TiO2 orientation which is a key focus for this paper. We used these models as the starting point for MD simulations run at 298 K for 40 ns
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