Ruthenium(II)- bipyridyl with extended π-system: Improved thermo-stable sensitizer for efficient and long-term durable dye sensitized solar cells

Abstract

A new extended thermo-stable high molar extinction coefficient bipyridyl ruthenium(II) complex "cis-Ru(4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine)(Ln)(NCS) 2 H101", where Ln = 4,4'-dicarboxylic acid-2,2'-bipyridine; was synthesized and characterized by 1 H-NMR, FT-IR and ESI-MASS spectroscopes. The H101 sensitized solar cell constructed with an active area of 0.54 cm 2 in combination with an ionic liquid electrolyte exhibited broader photocurrent action spectrum with solar-to-electric energy conversion efficiency (η) of 5.89 (J SC = 12.14 mA/cm 2 , V OC = 690 V, fill factor = 0.699) under Air Mass (AM) 1.5 sunlight, while the reference 'cis-Ru(4,4'-dinonyl-2,2'-bipyridine)(Ln)(NCS) 2 ', Z907 sensitized solar cell exhibited η-value of 5.17% (J SC = 11.93 mA/cm 2 , V OC = 650 V, fill factor = 0.666). TGA analysis of H101 showed extended thermal-stability and under continuous light exposure and aging at 55 • C, the DSSC retained 85% of its initial η-value, while under comparable conditions Z907 sensitized solar cell retained 88%. As compared to 4,4'-dinonyl-2,2'-bipyridine in Z907, the new ancillary bipyridyl ligand '4,4'bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine' in H101 shifts the absorption bands remarkably towards blue. The Density Functional Theory (DFT) and Time-Dependent DFT excited state calculations of the new sensitizer show that the first three HOMOs have t2g character with sizeable mixing from the NCS ligands with π-bonding orbitals of 4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine. The LUMO is a π *-orbital localized on the 4,4-dicarboxylic acid-2,2'-bipyridine and higher unoccupied frontier orbitals have π *-combinations with 4,4'-bis(3,5-di-tert-butylphenyl)-2,2'-bipyridine.

Enhanced dye sensitized solar cell performance with high surface area thin ZnO film and PEDOT:PSS

“…Coating of high band gap material over TiO 2 layer might enhances the loading of the dye, results in increase in absorption (Chou et al, 2012;Chandrasekharam et al, 2011). The higher amount of dye molecules is attributed to the higher basicity of the TiO 2 /ZnO electrode compared to the TiO 2 electrode.…”

Towards the Development of Functionalized PolypyridineLigands for Ru(II) Complexes as Photosensitizers inDye-Sensitized Solar Cells (DSSCs)

“…Numerous attempts have been made to molecularly engineer ruthenium sensitizers to broaden the absorption band and increase the molar extinction coefficient. One successful approach taken by various authors has been the functionalization of one arm of the 4,4'-dicarboxylic 2,2'-bipyridyl anchoring ligands in the N3 ruthenium sensitizer with different arrays of highly conjugated ancillary ligands, for example, 2-hexylthiophene ( HRS-1 ) [3,50], dialkylaminobenzene [51], alkyl bithiophene [52], alkoxybenzene, 2-(4- tert -butyloxyphenyl)ethylene [53,54], dipyridylamine [55], 3,4-ethylenedioxy- thien-2-yl)vinylene [56], 3,5-di- tert -butylbenzene [57], and 4,4-bis(4- tert -butylstyryl) [58], to form new ruthenium(II) polypyridyl dyes in order to enhance both the molar extinction coefficient and red-shift of the metal-to-ligand charge transfer (MLCT) wavelength of the complexes for the DSSCs application. The high molar extinction coefficients and red shift results obtained from such molecular designs were adduced to the extension of the π-conjugation in the complexes due to the introduction of these various groups.…”

Change of Dye Bath for Sensitisation of Nanocrystalline Films: Enhances Performance of Dye-Sensitized Solar Cells

“…The electrochemical properties of HRD2 and H102 dyes scrutinized by cyclic voltammetry using an electrolyte of tetrabutyl ammonium perchlorate (0.1 M in acetonitrile) and ferrocene as an internal standard at 0.42 V versus SCE [25][26][27]. The oxidation potentials for HRD2 and H102 sensitizers were 0.80 and 0.816 V versus SCE, respectively, while the reduction potentials were −0.758 and −0.94 V versus SCE, respectively.…”

“…As a part of our continued program on synthesis of new materials and their evaluation in DSSC performance, we have synthesized various sensitizers especially extended πconjugated bipyridyl-based ruthenium(II) complexes for efficient and long-term durability DSSCs [21][22][23][24]. We have also demonstrated in our laboratory that extended πconjugation with styryl group on the ancillary bipyridine increases the molar extinction coefficient of the ruthenium sensitizer but reduces the solubility, whereas extension of conjugation by directly electronically connecting the aryl groups on the ancillary bipyridines increases solubility and also improves overall photovoltaic performance of the DSSC test cells significantly [25][26][27]. Effect of different dye baths and dye-structures on the performance of dye sensitized solar cells based on triphenylamine organic dyes has been reported recently [28].…”