Are Alkynyl Spacers in Ancillary Ligands in Heteroleptic Bis(diimine)copper(I) Dyes Beneficial for Dye Performance in Dye-Sensitized Solar Cells?

Abstract

The syntheses of 4,4′-bis(4-dimethylaminophenyl)-6,6′-dimethyl-2,2′-bipyridine (1), 4,4′-bis(4-dimethylaminophenylethynyl)-6,6′-dimethyl-2,2′-bipyridine (2), 4,4′-bis(4-diphenylaminophenyl)-6,6′-dimethyl-2,2′-bipyridine (3), and 4,4′-bis(4-diphenylaminophenylethynyl)-6,6′-dimethyl-2,2′-bipyridine (4) are reported along with the preparations and characterisations of their homoleptic copper(I) complexes [CuL2][PF6] (L = 1–4). The solution absorption spectra of the complexes exhibit ligand-centred absorptions in addition to absorptions in the visible region assigned to a combination of intra-ligand and metal-to-ligand charge-transfer. Heteroleptic [Cu(5)(Lancillary)]+ dyes in which 5 is the anchoring ligand ((6,6′-dimethyl-[2,2′-bipyridine]-4,4′-diyl)bis(4,1-phenylene))bis(phosphonic acid) and Lancillary = 1–4 have been assembled on fluorine-doped tin oxide (FTO)-TiO2 electrodes in dye-sensitized solar cells (DSCs). Performance parameters and external quantum efficiency (EQE) spectra of the DSCs (four fully-masked cells for each dye) reveal that the best performing dyes are [Cu(5)(1)]+ and [Cu(5)(3)]+. The alkynyl spacers are not beneficial, leading to a decrease in the short-circuit current density (JSC), confirmed by lower values of EQEmax. Addition of a co-absorbent (n-decylphosphonic acid) to [Cu(5)(1)]+ lead to no significant enhancement of performance for DSCs sensitized with [Cu(5)(1)]+. Electrochemical impedance spectroscopy (EIS) has been used to investigate the interfaces in DSCs; the analysis shows that more favourable electron injection into TiO2 is observed for sensitizers without the alkynyl spacer and confirms higher JSC values for [Cu(5)(1)]+.

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

“…In [Cu(11)(35)] + and [Cu(11)(36)] + , the electron-donating NR 2 groups were expected to be beneficial in terms of stabilizing the hole remote from the TiO 2 surface. 208 Indeed, DSCs sensitized with these dyes performed well with respect to cells with the N719 reference dye (relative  = 33.4 and 36.0%, Table 5). However, as with the introduction of the imine functionality, inserting an alkyne unit between the phenylene and pyridine rings on going from ancillary ligand 35 to 37, or 36 to 38, resulted in significant decreases in J SC values and in overall PCEs (Table 5).…”

“…However, as with the introduction of the imine functionality, inserting an alkyne unit between the phenylene and pyridine rings on going from ancillary ligand 35 to 37, or 36 to 38, resulted in signicant decreases in J SC values and in overall PCEs (Table 5). 208 Ancillary ligands 39 and 40 (Scheme 18) represent rst and second generation hole-transport dendrons. Going from [Cu(11)(39)] + to [Cu(11)(40)] + leads to enhanced light absorption towards lower energies, and although DSCs with [Cu(11)(40)] + outperform those sensitized with [Cu(11)(39)] + , there was no gain in overall performance compared to the more structurally simple dyes listed in Table 5.…”

“…However, as with the introduction of the imine functionality, inserting an alkyne unit between the phenylene and pyridine rings on going from ancillary ligand 35 to 37, or 36 to 38, resulted in significant decreases in J SC values and in overall PCEs ( Table 5 ). 208 …”

Preparation and Characterization of Thin-Film Solar Cells with Ag/C60/MAPbI3/CZTSe/Mo/FTO Multilayered Structures

“…In the last decade, the power-conversion efficiency (PCE) of lead halide perovskite (CH 3 NH 3 PbX 3 , X = Cl, Br or I)-based thin film photovoltaic devices has been improved dramatically [5][6][7][8]. Organic metal halide materials have shown excellent properties for photon harvesting for solar cells, such as a low band gap and a large excitation diffusion length [9].…”

Recent Advances in Dye-Sensitized Solar Cells

“…Copper complexes also found application as dyes in DSSCs; Constable et al [ 3 ] reported the syntheses and characterization of four homoleptic copper (I) complexes and studied their performances in the cell. They underlined the importance of the ligand design, confirming that the introduction of alkynyl spacers between donor and acceptor moieties is not beneficial in terms of efficiency.…”