Helical Copper Redox Mediator with Low Electron Recombination for Dye-Sensitized Solar Cells

Abstract

Redox mediators play a major role in determining the photocurrent and photovoltage in dye-sensitized solar cells (DSSCs). Copper complexes are a good option for redox mediators but suffer from electron recombination. The traditional method is to add 4-(tert-butyl)pyridine (TBP) to the electrolyte, which is coordinated with the empty orbit of Ti, thereby slowing down the oxidized mediator's ability to capture electrons. However, this strategy will result in competitive coordination between the redox mediator and TBP, decreasing the stability of the device. In this study, two helical copper(I) complexes are synthesized and applied to TBP-free solar cells. La (1,3-bis(2,2′-bipyridin-6-yloxy)propane) and Lb (1,3-bis[(6′-methyl-2,2′-bipyridin-6-yl)oxy]propane) tend to form double-stranded helicates ([Cu 2 (Ln) 2 ] 2+ , n = a, b) rather than mononuclear complexes ([Cu(Ln)] + , n = a, b). To facilitate quantitative analysis of the complexes, Cu I Ln and Cu II Ln (n = a, b) are used as molecular formulae. Cu I La and Cu I Lb are characterized by electrospray mass spectroscopy, 1 H NMR spectroscopy, and electrochemistry. J−V measurement shows that both V oc and J sc increase with the increase of Cu I La concentration (below 0.1 M), and the best power conversion efficiency is 8.2%. The relationship between Cu(I) concentration and recombination for further study was measured by IMVS.

Solar energy conversion using first row d-block metal coordination compound sensitizers and redox mediators

“…8%, suggesting that the use of these dinuclear species is a promising way forward. 126 (1) Compatibility between ruthenium(II) dyes and Cu 2+ /Cu + redox couples in order to achieve high photoconversion efficiencies remains a challenge. ] + , and these DSCs represent state-of-the-art combinations of ruthenium(II) dyes and copper-based redox mediators.…”

“…8%, suggesting that the use of these dinuclear species is a promising way forward. 126 [Cu I L] + ⇌ [Cu II L] 2+ + e − [Cu I 2 L 2 ] 2+ ⇌ [Cu I Cu II L 2 ] 3+ + e − [Cu I Cu II L 2 ] 3+ ⇌ [Cu II 2 L 2 ] 4+ + e − [Cu I 2 L 2 ] 2+ ⇌ [Cu II 2 L 2 ] 4+ + 2e − …”

An Efficient Copper-Based Redox Shuttle Bearing a Hexadentate Polypyridyl Ligand for DSCs under Low-Light Conditions

“…Lewis bases, such as TBP and N -methylbenzimidazole (NMBI), are frequently used as additives in DSC devices to enhance the overall cell performance. − The enhancement observed with added Lewis bases is attributed to shifting the titania conduction band edge to more negative potentials and reducing the interfacial charge recombination rates by surface adsorption. ,− With most of the reported Cu-based RSs, TBP is known to coordinate with the Cu II species and even displace polydentate ligands, which has a significant impact on the redox potential as multiple redox species are produced, affecting the maximum achievable photovoltage and electron transfer kinetics. ,,,− In this context, the effect of TBP on the [Cu­(bpyPY4)] 2+/+ redox couple was evaluated in the presence of different concentrations of the Lewis base. TBP was added in excess of 10 equivalents relative to [Cu­(bpyPY4)] 2+ in solution to match the conditions used in the devices described below.…”

Copper-Templated Formation of Dihelical Oligothiophene–Phenanthroline Assemblies

“…In various examples it has been shown that appropriate functionalization of linear oligothiophenes with polar moieties such as peptides [31][32][33] or poly(ethylene oxide) 34 promote the formation of supramolecular nanostructures. Metal-assisted organization of symmetric OT-phen-based ligands into a dimeric dihelical arrangement should benefit from intermolecular π-π stacking interactions of the linear OT-linkers on one hand and from the preference of spherical d 10 -Cu(I) ions to adopt a pseudotetrahedral (D2d) coordination with α,α'-diamine ligands such as phen on the other hand.…”