A Series of Iron(II)‐NHC Sensitizers with Remarkable Power Conversion Efficiency in Photoelectrochemical Cells**

Abstract

A series of six new Fe(II)NHC-carboxylic sensitizers with their ancillary ligand decorated with functions of varied electronic properties have been designed with the aim to increase the metal-to-surface charge separation and light harvesting in iron-based dye-sensitized solar cells (DSSCs). ARM130 scored the highest efficiency ever reported for an iron-sensitized solar cell (1.83 %) using Mg 2 + and NBu 4 I-based electrolyte and a thick 20 μm TiO 2 anode. Computational modelling, transient absorption spectroscopy and electrochemical impedance spectroscopy (EIS) revealed that the electronic properties induced by the dimethoxyphenyl-substituted NHC ligand of ARM130 led to the best combination of electron injection yield and spectral sensitivity breadth.

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

“…A recent investigation from Gros and coworkers focused on heteroleptic dyes based upon 75 ( Scheme 27 ) and bearing different substituents in the 4-position of the pyridine ring of the ancillary ligand. 281 Substituents with varying electronic properties were selected and the most efficient dye was 81 ( Scheme 27 ). DSCs were fabricated with 20 μm thick TiO 2 photoanodes, and the optimized electrolyte composition described above, i.e.…”

“…DSCs were fabricated with 20 μm thick TiO 2 photoanodes, and the optimized electrolyte composition described above, i.e. LiI (0.1 M), I 2 (0.1 M), PMII (0.60 M), MgI 2 (0.1 M), Bu 4 NI (0.1 M) and GNCS (0.1 M) in MeCN; the counter electrode was coated with PEDOT rather than Pt, 281 even though in a previous study, Pt was shown to be more beneficial than PEDOT. 279 The best performance was found for dye 81 which incorporates electron-donating MeO groups ( Scheme 27 and Table 10 ).…”

“…From the results of EIS studies and computational modelling, it was concluded that 81 combines good light-harvesting and beneficial recombination kinetics. 281 Wärnmark and coworkers have recently reported the photophysical and electrochemical properties and DSC performances of heteroleptic dyes 82 and 83 ( Scheme 27 ) which incorporate electron-donating ancillary ligands. Time-resolved spectroscopy confirmed ultrafast (<100 fs) interfacial electron injection from dyes 82 and 83 into TiO 2 .…”

Panchromatic light harvesting and record power conversion efficiency for carboxylic/cyanoacrylic Fe(ii) NHC co-sensitized FeSSCs

“…32 Mg 2+ cations are capable to adsorb at the sensitizer/semiconductor interface and to improve the interfacial electron transfer kinetics (regeneration and/or electron injection), thus resulting in higher measured photocurrents. 33 This result was very recently further improved by our group up to reach the best efficiencies ever reported of 1.44 % (Jsc = 4.8 mA/cm 2 ) and 1.83% (Jsc = 4.8 mA/cm 2 ) by sensitizing FeSSCs respectively, with the heteroleptic complexes ARM13 33 and ARM130 34 (Figure 1). The heteroleptic approach was also recently applied by Warnmark that reported the introduction of diarylamino substituents on the central pyridine of the ancillary ligand resulting in 1.31% efficiency and Jsc = 3.5 mA/cm 2 .…”

Towards panchromatic Fe(ii) NHC sensitizersviaHOMO inversion

“…The MLCT lifetime has reached tens of picoseconds for complexes with tridentate C^N^C [18][19][20] and bidentate C^N ligands, [21][22][23][24] and nanoseconds for compounds bearing tridentate C^C^C ligands, 25 making it possible for iron to be used in photochemical applications such as iron-sensitized DSSCs. [26][27][28][29][30][31] However, apart from the recently published Fe(II) complex with phenN,N′^C ligands, 32 this improvement in lifetime was obtained at the sacrifice of achieving the panchromatic absorption required for solar energy conversion applications. Recently, "HOMO inversion" has emerged as a promising concept in the field.…”