Topical Collection "Coordination Complexes for Dye-Sensitized Solar Cells (DSCs)"

A topical collection in Inorganics (ISSN 2304-6740). This collection belongs to the section "Coordination Chemistry".

Editor

Guest Editor
Prof. Dr. Catherine Housecroft

Department of Chemistry, University of Basel, Basel, Switzerland
Website | E-Mail
Interests: Applications of coordination chemistry to sustainable energy; dye-sensitized solar cells using Earth abundant metals; emissive materials; light-emitting electrochemical cells; coordination networks; hierarchical assemblies for functional surfaces; water-splitting

Topical Collection Information

Dear Colleagues,

The Grätzel dye-sensitized solar cell (DSC) was developed in the 1990s and converts solar into electrical energy. Grätzel's breakthrough use of sintered nanoparticles of the semiconductor on the working electrode of the cell to provide a huge surface area for dye adsorption has been followed by the development of a myriad of sensitizers. The vast majority of investigations are focused on n-type DSCs. However, with an ultimate goal of functional tandem devices, much work is still needed to improve the performances of p-type DSCs. State-of-the-art dyes encompass ruthenium complexes, organic and zinc(II) porphyrin-based dyes with the best conversion efficiencies reaching ~11–14%. Copper(I)-based dyes are seen as sustainable alternatives to ruthenium-containing sensitizers and, with the aid of co-sensitization using an organic dye, have been shown to achieve efficiences of up to ~65% that of the benchmark rutheium(II) sensitizer N719. For p-type DSCs, cyclometallated ruthenium dyes show promise, and an emerging family of iridium-containing dyes has recently entered the field. This Special Issue aims to highlight the variety and importance of coordination complexes as sensitizers in DSCs.

Prof. Dr. Catherine E. Housecroft
Guest Editor

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Keywords

  • dye-sensitized solar cells
  • metal complexes
  • light-harvesting
  • solar energy conversion

Published Papers (7 papers)

2018

Open AccessReview NHC-Based Iron Sensitizers for DSSCs
Received: 25 May 2018 / Revised: 15 June 2018 / Accepted: 15 June 2018 / Published: 19 June 2018
Cited by 1 | PDF Full-text (12647 KB) | HTML Full-text | XML Full-text
Abstract
Nanostructured dye-sensitized solar cells (DSSCs) are promising photovoltaic devices because of their low cost and transparency. Ruthenium polypyridine complexes have long been considered as lead sensitizers for DSSCs, allowing them to reach up to 11% conversion efficiency. However, ruthenium suffers from serious drawbacks
[...] Read more.
Nanostructured dye-sensitized solar cells (DSSCs) are promising photovoltaic devices because of their low cost and transparency. Ruthenium polypyridine complexes have long been considered as lead sensitizers for DSSCs, allowing them to reach up to 11% conversion efficiency. However, ruthenium suffers from serious drawbacks potentially limiting its widespread applicability, mainly related to its potential toxicity and scarcity. This has motivated continuous research efforts to develop valuable alternatives from cheap earth-abundant metals, and among them, iron is particularly attractive. Making iron complexes applicable in DSSCs is highly challenging due to an ultrafast deactivation of the metal–ligand charge-transfer (MLCT) states into metal-centered (MC) states, leading to inefficient injection into TiO2. In this review, we present our latest developments in the field using Fe(II)-based photosensitizers bearing N-heterocyclic carbene (NHC) ligands, and their use in DSSCs. Special attention is paid to synthesis, photophysical, electrochemical, and computational characterization. Full article
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Open AccessArticle The Effect of Illumination Direction and Temperature on Dye-Sensitized Solar Cells with Viscous Cobalt Complex-Based Electrolytes
Received: 7 May 2018 / Revised: 5 June 2018 / Accepted: 6 June 2018 / Published: 12 June 2018
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Abstract
The illumination direction and temperature can greatly affect the performance of dye-sensitized solar cells (DSSCs) when practical non-volatile solvents are used with bulky one-electron redox mediators such as cobalt tris(bipyridine). For higher performance, a tandem electrolyte system consisting of cobalt tris(bipyridine) with tris(4-methoxyphenyl)amine
[...] Read more.
The illumination direction and temperature can greatly affect the performance of dye-sensitized solar cells (DSSCs) when practical non-volatile solvents are used with bulky one-electron redox mediators such as cobalt tris(bipyridine). For higher performance, a tandem electrolyte system consisting of cobalt tris(bipyridine) with tris(4-methoxyphenyl)amine was used. Discrepancies in JV hysteresis were investigated by using photocurrent turn-on transients, open-circuit voltage decay, and electrochemical impedance spectroscopy. The devices perform much better upon illumination form the counter electrode side and exhibit much less hysteresis and more stabilized power output as characterized by maximum power-point tracking (MPP) tracking. Full article
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Open AccessArticle The Versatile SALSAC Approach to Heteroleptic Copper(I) Dye Assembly in Dye-Sensitized Solar Cells
Received: 8 May 2018 / Revised: 23 May 2018 / Accepted: 23 May 2018 / Published: 25 May 2018
PDF Full-text (10350 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Surface-bound heteroleptic copper(I) dyes [Cu(Lanchor)(Lancillary)]+ are assembled using the “surfaces-as-ligands, surfaces as complexes” (SALSAC) approach by three different procedures. The anchoring and ancillary ligands chosen are ((6,6′-dimethyl-[2,2′-bipyridine]-4,4′-diyl)-bis(4,1-phenylene))bis(phosphonic acid) (3) and 4,4′-bis(4-iodophenyl)-6,6′-diphenyl-2,2′-bipyridine (4), respectively. In
[...] Read more.
Surface-bound heteroleptic copper(I) dyes [Cu(Lanchor)(Lancillary)]+ are assembled using the “surfaces-as-ligands, surfaces as complexes” (SALSAC) approach by three different procedures. The anchoring and ancillary ligands chosen are ((6,6′-dimethyl-[2,2′-bipyridine]-4,4′-diyl)-bis(4,1-phenylene))bis(phosphonic acid) (3) and 4,4′-bis(4-iodophenyl)-6,6′-diphenyl-2,2′-bipyridine (4), respectively. In the first SALSAC procedure, the FTO/TiO2 electrode is functionalized with 3 in the first dye bath, and then undergoes ligand exchange with the homoleptic complex [Cu(4)2][PF6] to give surface-bound [Cu(3)(4)]+. In the second method, the FTO/TiO2 electrode functionalized with 3 is immersed in a solution containing a 1:1 mixture of [Cu(MeCN)4][PF6] and 4 to give surface-anchored [Cu(3)(4)]+. In the third procedure, the anchor 3, copper(I) ion and ancillary ligand 4 are introduced in a sequential manner. The performances of the DSSCs show a dependence on the dye assembly procedure. The sequential method leads to the best-performing DSSCs with the highest values of JSC (7.85 and 7.73 mA cm−2 for fully masked cells) and overall efficiencies (η = 2.81 and 2.71%, representing 41.1 and 39.6% relative to an N719 reference DSSC). Use of the 1:1 mixture of [Cu(MeCN)4][PF6] and 4 yields DSSCs with higher VOC values but lower JSC values compared to those assembled using the sequential approach; values of η are 2.27 and 2.29% versus 6.84% for the N719 reference DSSC. The ligand exchange procedure leads to DSSCs that perform relatively poorly. The investigation demonstrates the versatile and powerful nature of SALSAC in preparing dyes for copper-based DSSCs, allowing the photoconversion efficiency of dye to be optimized for a given dye. The SALSAC strategy provides alternative hierarchical strategies where the isolation of the homoleptic [Cu(Lancillary)2]+ is difficult or time-consuming; stepwise strategies are more atom-economic than ligand exchange involving the homoleptic [Cu(Lancillary)2]+. Full article
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Open AccessArticle Copper Complexes with Tetradentate Ligands for Enhanced Charge Transport in Dye-Sensitized Solar Cells
Received: 28 April 2018 / Revised: 12 May 2018 / Accepted: 16 May 2018 / Published: 21 May 2018
Cited by 1 | PDF Full-text (2017 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In dye-sensitized solar cells (DSCs), the redox mediator is responsible for the regeneration of the oxidized dye and for the hole transport towards the cathode. Here, we introduce new copper complexes with tetradentate 6,6′-bis(4-(S)-isopropyl-2-oxazolinyl)-2,2′-bipyridine ligands, Cu(oxabpy), as redox mediators. Copper coordination
[...] Read more.
In dye-sensitized solar cells (DSCs), the redox mediator is responsible for the regeneration of the oxidized dye and for the hole transport towards the cathode. Here, we introduce new copper complexes with tetradentate 6,6′-bis(4-(S)-isopropyl-2-oxazolinyl)-2,2′-bipyridine ligands, Cu(oxabpy), as redox mediators. Copper coordination complexes with a square-planar geometry show low reorganization energies and thus introduce smaller losses in photovoltage. Slow recombination kinetics of excited electrons between the TiO2 and CuII(oxabpy) species lead to an exceptionally long electron lifetime, a high Fermi level in the TiO2, and a high photovoltage of 920 mV with photocurrents of 10 mA∙cm−2 and 6.2% power conversion efficiency. Meanwhile, a large driving force remains for the dye regeneration of the Y123 dye with high efficiencies. The square-planar Cu(oxabpy) complexes yield viscous gel-like solutions. The unique charge transport characteristics are attributed to a superposition of diffusion and electronic conduction. An enhancement in charge transport performance of 70% despite the higher viscosity is observed upon comparison of Cu(oxabpy) to the previously reported Cu(tmby)2 redox electrolyte. Full article
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Open AccessReview Ruthenium Complexes as Sensitizers in Dye-Sensitized Solar Cells
Received: 27 April 2018 / Revised: 16 May 2018 / Accepted: 17 May 2018 / Published: 21 May 2018
Cited by 1 | PDF Full-text (10625 KB) | HTML Full-text | XML Full-text
Abstract
In this review, we discuss the main directions in which ruthenium complexes for dye-sensitized solar cells (DSCs) were developed. We critically discuss the implemented design principles. This review might be helpful at this moment when a breakthrough is needed for DSC technology to
[...] Read more.
In this review, we discuss the main directions in which ruthenium complexes for dye-sensitized solar cells (DSCs) were developed. We critically discuss the implemented design principles. This review might be helpful at this moment when a breakthrough is needed for DSC technology to prove its market value. Full article
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Open AccessArticle Effects of Introducing Methoxy Groups into the Ancillary Ligands in Bis(diimine) Copper(I) Dyes for Dye-Sensitized Solar Cells
Received: 23 March 2018 / Revised: 5 April 2018 / Accepted: 6 April 2018 / Published: 10 April 2018
PDF Full-text (10785 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A systematic investigation of four heteroleptic bis(diimine) copper(I) dyes in n-type Dye-Sensitized Solar Cells (DSSCs) is presented. The dyes are assembled using a stepwise, on-surface assembly. The dyes contain a phosphonic acid-functionalized 2,2′-bipyridine (bpy) anchoring domain (5) and ancillary bpy ligands
[...] Read more.
A systematic investigation of four heteroleptic bis(diimine) copper(I) dyes in n-type Dye-Sensitized Solar Cells (DSSCs) is presented. The dyes are assembled using a stepwise, on-surface assembly. The dyes contain a phosphonic acid-functionalized 2,2′-bipyridine (bpy) anchoring domain (5) and ancillary bpy ligands that bear peripheral phenyl (1), 4-methoxyphenyl (2), 3,5-dimethoxyphenyl (3), or 3,4,5-trimethoxyphenyl (4) substituents. In masked DSSCs, the best overall photoconversion efficiency was obtained with the dye [Cu(5)(4)]+ (1.96% versus 5.79% for N719). Values of JSC for both [Cu(5)(2)]+ (in which the 4-MeO group is electron releasing) and [Cu(5)(4)]+ (which combines electron-releasing and electron-withdrawing effects of the 4- and 3,5-substituents) and are enhanced with respect to [Cu(5)(1)]+. DSSCs with [Cu(5)(3)]+ show the lowest JSC. Solid-state absorption spectra and external quantum efficiency spectra reveal that [Cu(5)(4)]+ benefits from an extended spectral range at higher energies. Values of VOC are in the order [Cu(5)(4)]+ > [Cu(5)(1)]+ > [Cu(5)(2)]+ > [Cu(5)(3)]+. Density functional theory calculations suggest that methoxyphenyl character in MOs within the HOMO manifold in [Cu(5)(2)]+ and [Cu(5)(4)]+ may contribute to the enhanced performances of these dyes with respect to [Cu(5)(1)]+. Full article
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Open AccessArticle Computational Treatments of Hybrid Dye Materials of Azobenzene and Chiral Schiff Base Metal Complexes
Received: 8 March 2018 / Revised: 27 March 2018 / Accepted: 27 March 2018 / Published: 28 March 2018
Cited by 1 | PDF Full-text (8675 KB) | HTML Full-text | XML Full-text
Abstract
Molecular orientation of dyes must be one of the important factors for designing dye-sensitized solar cells (DSSC). As model systems, we have prepared new hybrid materials composed of azobenzene (AZ) and chiral Schiff base Cu(II) complexes (pn(S)Cu and
[...] Read more.
Molecular orientation of dyes must be one of the important factors for designing dye-sensitized solar cells (DSSC). As model systems, we have prepared new hybrid materials composed of azobenzene (AZ) and chiral Schiff base Cu(II) complexes (pn(S)Cu and pn(R)Cu) in polymethyl methacrylate (PMMA) cast films. In addition to experimental results, in order to understand their behavior due to anisotropic alignment of them by linearly polarized UV light irradiation, the so-called Weigert effect, we treated theoretically and discussed based on computational chemistry and mathematical treatments (MD simulation and Bayesian statistics). Full article
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