Refining the anchor: Optimizing the performance of cyclometallated ruthenium(II) dyes in p-type dye sensitized solar cells

Abstract

A comparison of the performances of p-type dye sensitized solar cells (DSCs) sensitized by three cyclometallated ruthenium(II) dyes differing in their anchoring domains is presented. The dyes are [Ru(bpy)2(H1)] (H31 = (4-(2phenylpyridin-4-yl)phenyl)phosphonic acid) and the salts [ n Bu4N][Ru(bpy)2(1)] and [Ru(bpy)2(H2)][PF6] (H22 = (4-(2-phenylpyridin-4-yl)phenyl)carboxylic acid). DSCs were fabricated with FTO/NiO working electrodes and either an I-/I3-/MeCN or I-/I3-/MeCN:EtCN (3:1 by volume) electrolyte. The results confirm the higher performance of dyes with a phosphonate versus carboxylic acid anchor, and reveal that [Ru(bpy)2(H1)] (JSC = 3.24 mA cm-2 and η = 0.116%) performs better than [Ru(bpy)2(1)]-. Electrochemical impedance spectroscopy (EIS) shows that a DSC with [Ru(bpy)2(H1)] offers the lowest transport and recombination resistances and the shortest hole lifetime and diffusion length.

A Phosphonic Acid Anchoring Analogue of the Sensitizer P1 for p-Type Dye-Sensitized Solar Cells

“…All cells show similar fill-factors which, although low, are typical of p-type DSCs [10]. In comparison to our earlier work in which P1 gave values of V OC in the range 82-97 mV and J SC values between 1.84 and 2.76 mA cm −2 [21][22][23], the DSCs in Table 1 with sensitizer P1 achieve significantly higher values of V OC , but lower values of J SC . We attribute the differences to a change in the method of fabrication of the working electrodes (see Section 2.3), with the use of both pre-and post-treatments with Ni(OAc) 2 [32] proving beneficial.…”

“…Values of R t , R rec and Q µ are derived from the individual values of r t , r rec and q µ [34][35][36] and the resistance and constant phase element of the platinum counter electrode (R CE , Q CE ). A CPE was used for charge transfer processes at both the NiO working electrode and platinum counter electrode due to the different porosity of the electrode surfaces [38]; we have previously detailed the equation used to calculate the fitted capacitance (C µ ) [21]. Table 2.…”

“…Pellegrin et al have demonstrated that the ruthenium dye 1 (Scheme 2) with values of J SC = 0.78 mA cm -2 , V OC = 95 mV and η = 0.025%, has a comparable performance to C343 in a p-type DSC and outperforms an analogous [Ru(bpy) 3 ] 2+ -based dye with CO 2 H anchors [20]. Similarly, DSCs with the zwitterionic cyclometallated ruthenium dye 2 (Scheme 2) give photoconversion efficiencies that exceed those of cells sensitized by an analogous dye bearing a CO 2 H anchor [21,22] and we have shown that values of J SC up to 4.13 mA cm −2 and η up to 0.139% can be achieved using 2, with solvent and NiO fabrication playing critical roles in optimizing the performance [23]. We were therefore motivated to investigate an analogue of dye P1 which contains a PO(OH) 2 rather than CO 2 H acid anchoring group; the structure of this PP1 dye is shown in Scheme 1.…”

Structure of Ni(OH)2 intermediates determines the efficiency of NiO-based photocathodes – a case study using novel mesoporous NiO nanostars

“…maximum PCE of 0.079-0.116%. [54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] The performance of DSSCs using different NiO nanostructures is further evaluated by electrochemical impedance spectroscopy (EIS, Fig. 6b).…”

Where Are the tpy Embraces in [Zn{4′-(EtO)2OPC6H4tpy}2][CF3SO3]2?

“…Phosphonic acid anchoring groups have been shown to bind more strongly to semiconductor oxide surfaces than carboxylic acids and we have been particularly interested in the use of the phosphonic acid anchoring ligands shown in Scheme 1. The phosphonic acid anchor has been shown to be effective in complexes containing {Ru(bpy) 2 (CˆN)} + [11,12], {Cu(bpy) 2 } + [13,14], and {Zn(tpy) 2 } + [15,16] cores (CˆN = a cyclometallating ligand such as the conjugate base of 2-phenylpyridine, bpy = 2,2 -bipyridine), and we have demonstrated that, in copper-based dyes, the presence of both a 1,4-phenylene spacer between a bpy metal-binding domain and the phosphonic acid is beneficial to DSC performance [17]. The tpy derivative shown in Scheme 1 has been used in a number of {Ru(tpy) 2 } + -and {Zn(tpy) 2 } + -based dyes [15][16][17][18][19][20][21][22], and theoretical studies indicate that the presence of the 1,4-phenylene spacer enhances the rate of electron-transfer across the dye/semiconductor interface [23].…”