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

Abstract

A Cu complex featuring a hexadentate ligand was synthesized and evaluated as a redox shuttle in dye-sensitized solar cell (DSC) devices, which exhibited excellent performance under low-light conditions. Cu-based redox shuttles (RSs) have been shown to perform remarkably well under low-light conditions; however, most of the known Cu-based RSs employ bidentate pyridyl ligands and often require bulky flanking groups adjacent to the nitrogen donors of these ligands to prevent distortion and binding of exogenous Lewis bases such as 4-tert-butylpyridine (TBP) that are added to enhance cell performance. Without the bulky substituents, the bidentate ligands are susceptible to ligand exchange with TBP. In this context, we have developed a Cu-based RS with a preorganized multidentate ligand designed to facilitate efficient electron transfer kinetics and high stability via the chelate effect. The Cu system, [Cu­(bpyPY4)]2+/+, reported here is supported by the hexadentate polypyridyl ligand bpyPY4 (6,6′-bis­(1,1-di­(pyridine-2-yl)­ethyl)-2,2′-bipyridine) and examined as a RS in DSCs. From X-ray crystallography and variable-temperature 1H NMR studies, bpyPY4 provides a dynamic coordination environment around the metal center. Cyclic voltammetry and UV–visible and NMR spectroscopy indicate that noncoordinated pyridyl donors block binding of TBP to copper. DSC devices using [Cu­(bpyPY4)]2+/+ as the redox electrolyte gave a power conversion efficiency (PCE) value of 4.9% under 1 sun illumination (100 mW/cm2). Strikingly, the device performance increased to 11.11% when irradiated with 2400 lux (0.5 mW/cm2) via a fluorescent lamp light source and improved further to 15.2% PCE at 13500 lux (2.10 mW/cm2). The Cu redox shuttle is an intriguing candidate for implementation with narrow band gap sensitizers with low oxidation potentials, which are important for high photocurrent DSC devices.

Open-Cage Copper Complexes Modulate Coordination and Charge Transfer

“…This self-exchange rate constant is about an order of magnitude faster, with an ∼0.25 eV lower inner-sphere reorganization energy, compared to other related cobalt and copper cage complexes that undergo a change in coordination number upon electron transfer which we attribute to the more strained geometry of the ligand preventing larger structural changes in the backbone. 25,30 Thus, [Cu(PY5)] + should be a better dye regenerator and result in high current densities. The behavior of the [Cu(PY5)] 2+/+ complexes in DSSCs and the effects of TBP were therefore investigated by fabricating devices with various concentrations of TBP.…”

Panchromatic NIR-Absorbing Sensitizers with a Thienopyrazine Auxiliary Acceptor for Dye-Sensitized Solar Cells

“…Each of these bilayers also generates a capacitance, one of which is the chemical capacitance based on the charge accumulation in TiO 2 ( C μ ) and the other is the chemical capacitance at the electrolyte–counter electrode interface ( C CE ). From R rec and C μ , the lifetime of an electron in the TiO 2 semiconductor can be determined via the equation, τ TiO2 = R rec × C μ . Optimized Y123 / WM2 devices demonstrate a larger recombination resistance than Y123 / WM1 devices ( R rec = 91 and 38 Ω, respectively), and longer electron lifetimes in TiO 2 (τ TiO 2 = 81 and 9 ms, respectively).…”

“…From R rec and C μ , the lifetime of an electron in the TiO 2 semiconductor can be determined via the equation, τ TiO2 = R rec × C μ . 58 S7 and Figure S10).…”

Novel Metal Complexes Unit of Phenanthroline Derivative for Being Used as Auxiliary Electron Acceptor in Dye Sensitizer Molecules

“…In recent years, the energy resource has become a critical issue worldwide and the solar energy as a clean and sustainable energy has received widely attention. Solar cells are considered as one of the key technologies for using solar energy [1] . Great efforts have been invested in finding better photovoltaic materials to effectively take advantage of solar irradiation [2] .…”

“…Solar cells are considered as one of the key technologies for using solar energy. [1] Great efforts have been invested in finding better photovoltaic materials to effectively take advantage of solar irradiation. [2] The dye sensitized solar cells (DSSCs) was first reported by Gratzel and colleagues in Switzerland in 1991.…”