Abstract

A new series of tris-(bipyridyl)ruthenium-like complexes based on the 4-tripheylamine-2,2’:6’,2’’-terpyridine (TPA) push-pull ligand was prepared by incorporation of 4-carboxypyridine (cpy), 4,4’-dicarboxi-2,2’-bipyridine (dcbpy) and 4-carboxyterpyridine ligands (ctpy) ligands, in order to adsorb them on TiO2 in different anchoring conformations. The electron photoinjection and electron recombination processes of the respective dye-sensitized solar cells were greatly influenced by the molecular structure, which defined the surface concentration and surface charge on TiO2, such that the photoconversion efficiency was 10 times larger for [Ru(py)(dcbpy)(TPAtpy)] than for the [Ru(cpy)(bpy)(TPAtpy)](PF6) dye. Molecules anchoring in a more upright position and by a larger number of sites were shown to enhance the electron injection into TiO2 conduction band (CB) improving the short-circuit current (JSC), open circuit voltage (Voc) and the overall photoconversion efficiency. However, a positive net charge in the dye increased the back electron-transfer reactions and induced a decrease in both Voc and conversion efficiency.

Highlights

  • The development of our society is strongly dependent on energy, it is fundamental finding new and efficient alternatives such as based on solar energy

  • Most fundamental step in the process, which depends on properties such as having (i) an anchoring group for efficient electronic communication with the semiconductor,[2] (ii) suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) potentials relative to TiO2 conduction band edge and electrolyte (I-/I3-) redox potential,[3,10,11] and (iii) as broad absorption spectrum in the visible and near infrared region, with (iv) high molar absorptivities (ε).[12]

  • The electron photoinjection and electron recombination in the respective dye-sensitized solar cells were greatly influenced by the molecular structure, as well as by their charge and surface concentration (Scheme 1), such that the photoconversion efficiency was 10 times larger for [Ru(py)(dcbpy)(TPAtpy)] than for the [Ru(cpy)(bpy)(TPAtpy)]+ dye

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Summary

Introduction

The development of our society is strongly dependent on energy, it is fundamental finding new and efficient alternatives such as based on solar energy. The sensitizers are usually designed with extended π conjugation frameworks and strengthened intramolecular charge transfer (ICT) by using suitable donors and acceptors.[13,14,15,16,17] Concerning the donor, many sensitizers based on carbazole, indoline, Vol 31, No 11, 2020 phenothiazine, thiophene and perylene have been developed for fabricating DSSCs with high performance.[13,14,15,16,17] For designing efficient sensitizers, it is crucial to select an excellent donor In this context, triphenylamine moieties have been extensively applied because of their strong electron-donating character, which may be favorable for extending the absorption spectra by improving the ICT outcome.[13,14,15,16,17] The donor-acceptor sensitizers with rod-like shape are been extensively explored but the elongated structure may facilitate the formation of aggregates[18] and the recombination with the triiodide ion in the electrolyte solution. This scenario is changed by the organic electron-donor unit in order to realize push-pull type ruthenium dye exhibiting additional strong intraligand charge-transfer (ILCT) bands in the visible region

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