Strategies for Optimizing the Performance of Cyclometalated Ruthenium Sensitizers for Dye‐Sensitized Solar Cells

Abstract

Pursuant to our goal of optimizing the performance of cyclometalated Ru sensitizers in the dye-sensitized solar cell (DSSC), the physicochemical properties of a series of tris-heteroleptic Ru II complexes are reported. Each of these complexes contains a metal ligated by: (i) a bidentate 2,2Ј-bipyridine-4,4Ј-dicarboxylic acid (dcbpy) ligand to anchor the dye to the TiO 2 surface; (ii) a cyclometalating ligand -with electron-withdrawing groups to ensure a sufficiently high oxidation potential for dye regeneration in the DSSC; and

A Trisheteroleptic Cyclometalated RuII Sensitizer that Enables High Power Output in a Dye‐Sensitized Solar Cell

“…[20] Briefly, the cyclometalating ligand, ppy-(CF 3 ) 2 , which was synthesized by a Negishi coupling of 2-pyridylzinc bromide and 1-bromo-2,4-bis(trifluoromethyl)benzene, [Ru(C 6 H 6 )Cl 2 ] 2 , NaOH, and KPF 6 were reacted to furnish [Ru(CH 3 CN) 4 (ppy-(CF 3 ) 2 )]PF 6 . This complex was then treated with deeb (4,4'-diethylester-2,2'-bipyridine) and dthbpy (2,2'-bis(5-hexylthiophen-2-yl)-2,2'-bipyridine) to give the ethylester intermediate [Ru-(deeb)(dthbpy)(ppy-(CF 3 ) 2 )]PF 6 , which affords 3 in high purity upon saponification.…”

“…[10,11,[15][16][17][18] This scenario leaves open the opportunity to replace one dcbpy with a bidentate ligand capable of suppressing recombination and enhancing the optical properties as per the aforementioned protocol (Scheme 1). [2,19] While we recently demonstrated synthetic access to trisheteroleptic Ru sensitizers (e.g., 1 and 2; Scheme 2), [20] we learned that removing the acid linkers raises the HOMO level of the sensitizer to potentially compromise dye regeneration. (The HOMO level of the sensitizer must lie lower in energy than the I À /I 3 À redox couple that resides at approximately + 0.5 V vs. normal hydrogen electrode (NHE).…”

“…[2,19] While we recently demonstrated synthetic access to trisheteroleptic Ru sensitizers (e.g., 1 and 2; Scheme 2), [20] we learned that removing the acid linkers raises the HOMO level of the sensitizer to potentially compromise dye regeneration. (The HOMO level of the sensitizer must lie lower in energy than the I À /I 3 À redox couple that resides at approximately + 0.5 V vs. normal hydrogen electrode (NHE).[21] Although the HOMO of 1 lies at + 0.70 V vs. NHE and therefore meets this criterion, [20] champion Ru-based sensitizers all have oxidation potentials higher than ca. + 0.9 V.…”

Sticking and patching: tuning and anchoring cyclometallated ruthenium(ii) complexes

“…The potential for enhanced photon-to-current conversion efficiencies has prompted active exploration of cyclometallated ruthenium(II) sensitizers for n-type DSCs. 8,10,11 The effects of combining [Ru(N^N) 2 (C^N)] + sensitizers with the cobalt-based redox shuttle [Co(dmbpy) 3 ] 3+/2+ (dmbpy = 4,4'-dimethyl-2,2'-bipyridine) have also recently been reported. 12 In [Ru(N^N) 2 (C^N)] + dyes for n-type DSCs, the cyclometallating domain constitutes the ancillary ligand.…”

The BCL Approach for the Molecular Design of New Ruthenium Complexes for Dye Sensitized Solar Cells

“…All calculations were performed on the ADF 2010 package [12]. Geometry optimization of ligands and complexes (ground state and first triplet), was performed with the PBE exchange correlation functional in conjunction with DZP quality basis set for first row elements and ZORA-TZP basis set for transition metals (Ru,Ti).…”