Iron-Sensitized Solar Cells (FeSSCs).

ConspectusThe harvesting and conversion of solar energy have become a burning issue for our modern societies seeking to move away from the exploitation of fossil fuels. In this context, dye-sensitized solar cells (DSSCs) have proven to be trustworthy alternatives to silicon-based cells with advantages in terms of transparency and efficiency under low illumination conditions. These devices are highly dependent on the ability of the sensitizer that they contain to collect sunlight and transfer an electron to a semiconductor after excitation. Ruthenium and polypyridine complexes are benchmarks in this field as they exhibit ideal characteristics such as long-lasting metal-ligand charge transfer (MLCT) states and efficient separation between electrons and holes, limiting recombination at the dye-semiconductor interface. Despite all of these advantages, ruthenium is a noble metal, and the development of more sustainable energy devices based on earth-abundant metals is now a must. A quick glance at the periodic table reveals iron as a potential good candidate, since it belongs to the same group of ruthenium, which suggests similar electronic properties. However, striking photophysical differences exist between ruthenium(II) polypyridyl complexes and their Fe(II) analogues, the latter suffering from short-lived MLCT states resulting of their ultrafast relaxation into metal-centered (MC) states. Pyridyl-N-heterocyclic carbenes (pyridylNHC) brought a strong σ-donor character required to promote a higher ligand field splitting of the iron d orbitals. This induces destabilization of the MC states over the MLCT manifold and a consequent slowdown of the excited states deactivation providing iron(II) complexes with tens of picoseconds lifetimes, making them more promising for applications in DSSCs. This Account highlights our recent advances in the development and characterization of iron-sensitized solar cells (FeSSCs) with a focus on the design of efficient sensitizers going from homoleptic to heteroleptic complexes (bearing different anchoring groups) and the tuning of electrolyte composition. Our rational approach led to the best photocurrent and efficiency ever reported for an iron sensitized solar cell (2% PCE and 9 mA/cm2) using a cosensitization process. This work clearly evidences that the solar energy conversion based on iron complex sensitization is now an opened and fruitful route.

Operando double-edge high-resolution X-ray absorption spectroscopy study of BiVO4 photoanodes.

High energy resolution fluorescence detected X-ray absorption spectroscopy is a powerful method for probing the electronic structure of functional materials. The X-ray penetration depth and photon-in/photon-out nature of the method allow operando experiments to be performed, in particular in electrochemical cells. Here, operando high-resolution X-ray absorption measurements of a BiVO4 photoanode are reported, simultaneously probing the local electronic states of both cations. Small but significant variations of the spectral lineshapes induced by the applied potential were observed and an explanation in terms of the occupation of electronic states at or near the band edges is proposed.

Designing Ionic Ir(III) Cyclometalated Complexes as Photocatalysts for Light Assisted ATRP of MMA. A Combined Experimental and Mechanistic Study.

A new family of ionic Ir(III) cyclometalated complexes with general formula [Ir(CN)2(NN)][Br], was designed and prepared to be assessed as photocalysts for the visible light assisted ATRP polymerization of MMA. To this purpose, our design strategy involved both: i) the decoration of the cyclometalating (CN) and the ancillary (NN) ligands with various electron withdrawing and/or electron donor substituents and, ii) the use of Br- as the counter anion for these cationic Ir(III) species. After an extensive screening in which the [Ir(CN)2(NN)][Br]-type compounds were compared to the model neutral complex fac-[Ir(ppy)3], the "fully" amino-substituted ion pairs abbreviated as [10][Br] and [11][Br], exhibited the best photocatalytic performances under irradiation with CFL lamps. It is worth noting that the outcomes of transient absorption spectroscopy (TAS) experiments combined with theoretical DFT calculations, enlightened the role played by the Ir(III) complexes in the mechanism of the photoATRP process, and suggested the rationalization of the different performances that were highlighted by our Ir(III) catalyst in the visible light assisted photopolymerization of MMA.

Electrocatalytic Poly(3,4-ethylenedioxythiophene) for Electrochemical Conversion of 5-Hydroxymethylfurfural.

This study investigates the utilization of the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) as a catalytic material for the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). PEDOT films doped with different counterions were electrodeposited on graphite foil. In particular, the mobile anion perchlorate and the polymeric ionomers polystyrenesulfonate, Nafion, and Aquivion were used. The electrocatalytic properties of PEDOT films were evaluated toward the TEMPO redox mediator in the absence and the presence of HMF as a substrate for oxidation reactions. The electrocatalytic HMF oxidation was confirmed to occur at PEDOT electrodes, and it was also found that the chemical nature of PEDOT counterions controls the electrocatalytic conversion of HMF by modulating the kinetics of the electrochemical generation of the oxoammonium cation TEMPO(+). Potentiostatic electrolysis experiments showed that both the reference graphite electrode and PEDOT substrates were able to convert HMF to FDCA with an 80% faradaic efficiency (FE) and a >90% yield (FDCA), but, compared to graphite, the complete conversion of HMF to FDCA required a ca. 30% shorter time when using PEDOT electrodes doped with perchlorate or Aquivion, thanks to their ability to sustain a higher current density in the initial phase of the electrolysis. In addition, while all PEDOT films were chemically stable under the electrochemical conditions herein described, only PEDOT films doped with Aquivion were also mechanically robust and stable against delamination. Thus, the new PEDOT/Aquivion composite may represent the best choice for the implementation of PEDOT-based electrodes in TEMPO-mediated electrocatalytic applications.

Metal Complexes for Dye-Sensitized Photoelectrochemical Cells (DSPECs).

Since Mallouk's earliest contribution, dye-sensitized photoelectrochemical cells (DSPECs) have emerged as a promising class of photoelectrochemical devices capable of storing solar light into chemical bonds. This review primarily focuses on metal complexes outlining stabilization strategies and applications. The ubiquity and safety of water have made its splitting an extensively studied reaction; here, we present some examples from the outset to recent advancements. Additionally, alternative oxidative pathways like HX splitting and organic reactions mediated by a redox shuttle are discussed.

Antibactericidal Ir(III) and Ru(II) Complexes with Phosphine-Alkaloid Conjugate and Their Interactions with Biomolecules: A Case of N-Methylphenethylamine.

The phosphine ligand (Ph2 PCH2 N(CH3 )(CH2 )2 Ph, PNMPEA) obtained by the reaction of the (hydroxymethyl)diphenylphosphine with naturally occurring alkaloid N-methylphenethylamine, was used to synthesize the half-sandwich iridium(III) (Ir(η5 -Cp*)Cl2 Ph2 PCH2 N(CH3 )(CH2 )2 Ph, IrPNMPEA) and ruthenium(II) (Ru(η6 -p-cymene)Cl2 Ph2 PCH2 N(CH3 )(CH2 )2 Ph, RuPNMPEA) complexes. They were characterized using a vast array of methods, including 1D and 2D NMR, ESI(+)MS spectrometry, elemental analysis, cyclic voltammetry (CV), electron spectroscopy in the UV-Vis range (absorption, fluorescence) and density functional theory (DFT). The initial antimicrobial activity in vitro toward Gram-positive and Gram-negative bacterial strains was examined, indicating that both complexes are selective towards Gram-positive bacteria, e. g., Staphylococcus aureus, where the IrPNMPEA has been more bactericidal compared to RuPNMPEA. Additionally, the interactions of these compounds with various biomolecules, such as DNA (ctDNA, plasmid DNA, 9-ethylguanine (9-EtG), and 9-methyladenine (9-MeA)), nicotinamide adenine dinucleotide (NADH), glutathione (GSH), and ascorbic acid (Asc) were described. The results showed that both Ir(III) and Ru(II) complexes accelerate the oxidation process of NADH, GSH and Asc that appeared to occur by an electron transfer mechanism. Interestingly, only IrPNMPEA leads to the formation of various biomolecule adducts, which can explain its higher activity. Furthermore, RuPNMPEA and IrPNMPEA have been interacting with the DNA through weak noncovalent interactions.

Photoredox Cross-Dehydrogenative Coupling of N-Aryl Glycines Mediated by Mesoporous Graphitic Carbon Nitride: An Environmentally Friendly Approach to the Synthesis of Non-Proteinogenic α-Amino Acids (NPAAs) Decorated with Indoles.

Indole-decorated glycine derivatives are prepared through an environmentally benign cross-dehydrogenative coupling between N-aryl glycine analogues and indoles (yield of ≤81%). Merging heterogeneous organocatalysis and photocatalysis, C-H functionalization has been achieved by selective C-2 oxidation of N-aryl glycines to afford the electrophilic imine followed by Friedel-Crafts alkylation with indole. The sustainability of the process has been taken into account in the reaction design through the implementation of a metal-free recyclable heterogeneous photocatalyst and a green reaction medium. Scale-up of the benchmark reaction (gram scale, yield of 69%) and recycling experiments (over seven runs without a loss of efficiency) have been performed to prove the robustness of the protocol. Finally, mechanistic studies were conducted employing electron paramagnetic resonance spectroscopy to unveil the roles of the photocatalyst and oxygen in the formation of odd-electron species.

Liposomal Binuclear Ir(III)-Cu(II) Coordination Compounds with Phosphino-Fluoroquinolone Conjugates for Human Prostate Carcinoma Treatment.

Novel heteronuclear IrIII-CuII coordination compounds ([Ir(η5-Cp*)Cl2Pcfx-Cu(phen)](NO3)·1.75(CH3OH)·0.75(H2O) (1), [Ir(η5-Cp*)Cl2Pnfx-Cu(phen)](NO3)·1.75(CH3OH)·0.75(H2O) (2), [Ir(η5-Cp*)Cl2Plfx-Cu(phen)](NO3)·1.3(H2O)·1.95(CH3OH) (3), [Ir(η5-Cp*)Cl2Psfx-Cu(phen)] (4)) bearing phosphines derived from fluoroquinolones, namely, sparfloxacin (Hsfx), ciprofloxacin (Hcfx), lomefloxacin (Hlfx), and norfloxacin (Hnfx), have been synthesized and studied as possible anticancer chemotherapeutics. All compounds have been characterized by electrospray ionization mass spectrometry (ESI-MS), a number of spectroscopic methods (i.e., IR, fluorescence, and electron paramagnetic resonance (EPR)), cyclic voltammetry, variable-temperature magnetic susceptibility measurements, and X-ray diffractometry. The coordination geometry of IrIII in all complexes adopts a characteristic piano-stool geometry with the η5-coordinated and three additional sites occupied by two chloride and phosphine ligands, while CuII ions in complexes 1 and 2 form a distorted square-pyramidal coordination geometry, and in complex 3, the coordination geometry around CuII ions is a distorted octahedron. Interestingly, the crystal structure of [Ir(η5-Cp*)Cl2Plfx-Cu(phen)] features the one-dimensional (1D) metal-organic polymer. Liposomes loaded with redox-active and fluorescent [Ir(η5-Cp*)Cl2Pcfx-Cu(phen)] (1L) have been prepared to increase water solubility and minimize serious systemic side effects. It has been proven, by confocal microscopy and an inductively coupled plasma mass spectrometry (ICP-MS) analysis, that the liposomal form of compound 1 can be effectively accumulated inside human lung adenocarcinoma and human prostate carcinoma cells with selective localization in nuclei. A cytometric analysis showed dominance of apoptosis over the other cell death types. Furthermore, the investigated nanoformulations induced changes in the cell cycle, leading to S phase arrest in a dose-dependent manner. Importantly, in vitro anticancer action on three-dimensional (3D) multicellular tumor spheroids has been demonstrated.

Investigation on Sensing Performance of Highly Doped Sb/SnO2.

Tin dioxide (SnO2) is the most-used semiconductor for gas sensing applications. However, lack of selectivity and humidity influence limit its potential usage. Antimony (Sb) doped SnO2 showed unique electrical and chemical properties, since the introduction of Sb ions leads to the creation of a new shallow band level and of oxygen vacancies acting as donors in SnO2. Although low-doped SnO2:Sb demonstrated an improvement of the sensing performance compared to pure SnO2, there is a lack of investigation on this material. To fill this gap, we focused this work on the study of gas sensing properties of highly doped SnO2:Sb. Morphology, crystal structure and elemental composition were characterized, highlighting that Sb doping hinders SnO2 grain growth and decreases crystallinity slightly, while lattice parameters expand after the introduction of Sb ions into the SnO2 crystal. XRF and EDS confirmed the high purity of the SnO2:Sb powders, and XPS highlighted a higher Sb concentration compared to XRF and EDS results, due to a partial Sb segregation on superficial layers of Sb/SnO2. Then, the samples were exposed to different gases, highlighting a high selectivity to NO2 with a good sensitivity and a limited influence of humidity. Lastly, an interpretation of the sensing mechanism vs. NO2 was proposed.

Visible Light Reductive Photocatalysis of Azo-Dyes with n-n Junctions Based on Chemically Deposited CdS.

New composite photocatalysts have been obtained by chemical bath deposition of CdS on top of either nanostructured crystalline ZrO2 or TiO2 films previously deposited on conductive glass FTO. Their morphological, photoelectrochemical and photochemical properties have been investigated and compared. Time resolved spectroscopic, techniques show that in FTO/TiO2/CdS films the radiative recombination of charges, separated by visible illumination of CdS, is faster than in FTO/ZrO2/CdS, evidencing that carrier dynamics in the two systems is different. Photoelectrochemical investigation evidence a suppression of electron collection in ZrO2/CdS network, whereas electron injection from CdS to TiO2 is very efficient since trap states of TiO2 act as a reservoir for long lived electrons storage. This ability of FTO/TiO2/CdS films is used in the reductive cleavage of N=N bonds of some azo-dyes by visible light irradiation, with formation and accumulation of reduced aminic intermediates, identified by ESI-MS analysis. Needed protons are provided by sodium formate, a good hole scavenger that leaves no residue upon oxidation. FTO/TiO2/CdS has an approximately 100 meV driving force larger than FTO/ZrO2/CdS under illumination for azo-dye reduction and it is always about 10% more active than the seconds. The films showed very high stability and recyclability, ease of handling and recovering.

Optically Transparent Gold Nanoparticles for DSSC Counter-Electrode: An Electrochemical Characterization.

A gold nanoparticles transparent electrode was realized by chemical reduction. This work aims to compare the transparent gold nanoparticles electrode with a more commonly utilized gold-film-coated electrode in order to investigate its potential use as counter-electrode (CE) in dye-sensitized solar cells (DSSCs). A series of DSSC devices, utilizing I-/I3- and Co(III)/(II) polypyridine redox mediators [Co(dtb)3]3+/2+; dtb = 4,4'ditert-butyl-2,2'-bipyridine)], were evaluated. The investigation focused firstly on the structural characterization of the deposited gold layers and then on the electrochemical study. The novelty of the work is the realization of a gold nanoparticles CE that reached 80% of average visible transmittance. We finally examined the performance of the transparent gold nanoparticles CE in DSSC devices. A maximum power conversion efficiency (PCE) of 4.56% was obtained with a commercial I-/I3--based electrolyte, while a maximum 3.1% of PCE was obtained with the homemade Co-based electrolyte.

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

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 Mg2+ and NBu4 I-based electrolyte and a thick 20 µm TiO2 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.

Artificial photosynthesis: photoanodes based on polyquinoid dyes onto mesoporous tin oxide surface.

Dye-sensitized photoelectrochemical cells represent an appealing solution for artificial photosynthesis, aimed at the conversion of solar light into fuels or commodity chemicals. Extensive efforts have been directed towards the development of photoelectrodes combining semiconductor materials and organic dyes; the use of molecular components allows to tune the absorption and redox properties of the material. Recently, we have reported the use of a class of pentacyclic quinoid organic dyes (KuQuinone) chemisorbed onto semiconducting tin oxide as photoanodes for water oxidation. In this work, we investigate the effect of the SnO2 semiconductor thickness and morphology and of the dye-anchoring group on the photoelectrochemical performance of the electrodes. The optimized materials are mesoporous SnO2 layers with 2.5 µm film thickness combined with a KuQuinone dye with a 3-carboxylpropyl-anchoring chain: these electrodes achieve light-harvesting efficiency of 93% at the maximum absorption wavelength of 533 nm, and photocurrent density J up to 350 µA/cm2 in the photoelectrochemical oxidation of ascorbate, although with a limited incident photon-to-current efficiency of 0.075%. Calculations based on the density functional theory (DFT) support the role of the reduced species of the KuQuinone dye via a proton-coupled electron transfer as the competent species involved in the electron transfer to the tin oxide semiconductor. Finally, a preliminary investigation of the photoelectrodes towards benzyl alcohol oxidation is presented, achieving photocurrent density up to 90 µA/cm2 in acetonitrile in the presence of N-hydroxysuccinimide and pyridine as redox mediator and base, respectively. These results support the possibility of using molecular-based materials in synthetic photoelectrochemistry.

Photoelectrocatalytic degradation of emerging contaminants at WO3/BiVO4 photoanodes in aqueous solution.

WO3/BiVO4 films obtained by electrochemical deposition of BiVO4 over mesoporous WO3 were applied to the photoelectrochemical degradation of selected emerging contaminants (ketoprofen and levofloxacine) in aqueous solutions. The WO3/BiVO4 films in this work are characterized by a mesoporous morphology with a maximum photoconversion efficiency >40% extending beyond 500 nm in Na2SO4 electrolytes. Oxygen was found to be the dominant water oxidation product (ca. 90% faradaic yield) and no evidence for the photogeneration of OH radicals was obtained. Nevertheless, both 10 ppm levofloxacine and ketoprofen could be degraded at WO3/BiVO4 junctions upon a few hours of illumination under visible light. However, while levofloxacine degradation intermediates were progressively consumed by further oxidation at the WO3/BiVO4 interface, ketoprofen oxidation byproducts, being stable aromatic species, were found to be persistent in aqueous solution even after 15 hours of solar simulated illumination. This indicates that, due to the lower oxidizing power of photogenerated holes in BiVO4 and a different water oxidation mechanism, the employment of WO3/BiVO4 in photoelectrochemical environmental remediation processes is much less universal than that possible with wider band gap semiconductors such as TiO2 and WO3.

Electronic and charge transfer properties of bio-inspired flavylium ions for applications in TiO2-based dye-sensitized solar cells.

We present here a complete study on four synthetic environmentally friendly flavylium salts employed as sensitizers for dye-sensitized solar cells (DSSCs). The effect of several donor groups on the molecular structure of flavylium ions was investigated by combining electrochemical, spectroscopic and computational means. The computational investigation indicated that these molecules can interact strongly with the TiO2 surface by a single OH group of the dihydroxybenzene moiety, and can efficiently inject electrons into the TiO2 following the excitation of their lowest singlet states exhibiting charge transfer (CT) character. In general, all dyes within the explored series exhibited quite good regeneration efficiencies, often ≥70%, in the presence of an iodide electron donor, explaining the high IPCEs and photocurrents recorded in the presence of high lithium content electrolytes. The combination of molecular orbital calculations and electrochemical measurements has also revealed that the introduction of donor groups on the benzopyrylium ring has a generally positive effect resulting in an extended low energy light harvesting and in a potential improvement of the photoinduced charge separation at the semiconductor/dye/electrolyte interface. It also increases the reversibility of the oxidative redox processes of these bio-inspired species, a feature in favour of their long-term stability. At present the best dye within the explored series is 7-(N,N-diethylamino)-3',4'-dihydroxyflavylium chloride based on a dialkylamine donor which is capable of delivering, under optimized conditions, a short-circuit current density of 15 mA cm-2. This is the highest value so far obtained for synthetic analogues of anthocyanins.

Rapid Static Sensitizer Regeneration Enabled by Ion Pairing.

An anionic CoII complex, [Co(TTT) (NCS)3]- (TTT = 4,4',4″-tri-tert-butyl-2,2':6',2″-terpyridine and NCS = isothiocyanate), was synthesized for use in dye-sensitized solar cells (DSSCs). The CoII complex was found to ion-pair with the hexacationic sensitizer [Ru(tmam)2(dcb)]6+ (tmam = 4,4'-bis(trimethylaminomethyl)-2,2'-bipyridine and dcb = 4,4'-(CO2H)2-2,2'-bipyridine) anchored to TiO2 thin films immersed in acetonitrile solution. Visible light excitation of the ion pairs resulted in excited-state injection followed by rapid static regeneration of the oxidized sensitizer (<10 ns). The static component to regeneration gave an ion-pair equilibrium constant of 6000 M-1. This value is an order of magnitude smaller than the equilibrium constant determined for [Ru(tmam)2(deeb)]6+ (deeb = 4,4'-(CO2Et)2-2,2'-bipyridine) dissolved in acetonitrile. DSSC studies employing [Co(TTT) (NCS)3]- or the cationic [Co(DTB)3]2+ (DTB = 4,4'-di-tert-butyl-2,2'-bipyridine) as redox mediators revealed a 3 fold photocurrent increase in the presence of the anionic cobalt complex. As the regeneration step was greatly enhanced through the formation of Coulombic ion pairs, both electron injection and regeneration were complete within 10 ns which is unprecedented for dye-sensitization. The results obtained reveal that ground-state ion-pairing can be a powerful strategy for DSSC optimization.

Coupling of Zinc Porphyrin Dyes and Copper Electrolytes: A Springboard for Novel Sustainable Dye-Sensitized Solar Cells.

The combination of ß-substituted Zn2+ porphyrin dyes and copper-based electrolytes represents a sustainable route for economic and environmentally friendly dye-sensitized solar cells. Remarkably, a new copper electrolyte, [Cu(2-mesityl-1,10-phenanthroline)2]+/2+, exceeds the performance reached by Co2+/3+ and I-/I3- reference electrolytes.

Tetracoordinated Bis-phenanthroline Copper-Complex Couple as Efficient Redox Mediators for Dye Solar Cells.

A tetracoordinated redox couple, made by [Cu(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2][PF6], 1, and its Cu(II) form [Cu(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2][PF6]2, 2, has been synthesized, and its electrochemical and photochemical features have been investigated and compared with those of a previously published Cu(2+)/Cu(+) redox shuttle, namely, [Cu(2,9-dimethyl-1,10-phenanthroline)2][PF6], 3, and its pentacoordinated oxidized form [Cu(2,9-dimethyl-1,10-phenanthroline)2Cl][PF6], 4. The detrimental effect of the fifth Cl(-) ancillary ligand on the charge transfer kinetics of the redox shuttles has been exhaustively demonstrated. Appropriately balanced Cu-based electrolytes have been then formulated and tested in dye solar cells in combination with a π-extended benzothiadiazole dye. The bis-phenanthroline Cu-complexes, 1 and 2, have been found to provide an overall 4.4% solar energy conversion efficiency, which is more than twice that of the literature benchmark couple, 3 and 4, employing a Cl-coordinated oxidized species and even comparable with the performances of a I(-)/I3(-) electrolyte of analogous concentration. A fast counter-electrode reaction, due to the excellent electrochemical reversibility of 2, and a high electron collection efficiency, allowed through the efficient dye regeneration kinetics exerted by 1, represents two major characteristics of these copper-based electron mediators and may constitute a pivotal step toward the development of a next generation of copper-based efficient iodine-free redox shuttles.

Correction: On the stability of manganese tris(ß-diketonate) complexes as redox mediators in DSSCs.

Correction for 'On the stability of manganese tris(ß-diketonate) complexes as redox mediators in DSSCs' by Stefano Carli et al., Phys. Chem. Chem. Phys., 2016, 18, 5949-5956.

On the stability of manganese tris(ß-diketonate) complexes as redox mediators in DSSCs.

The photoelectrochemical properties and stability of dye sensitized solar cells containing Mn(ß-diketonato)3 complexes, [Mn(III)(acac)3] () (acac = acetylacetonate), [Mn(III)(CF2)3] () (CF2 = 4,4-difluoro-1-phenylbutanate-1,3-dione), [Mn(III)(DBM)3] () (DBM = dibenzoylmethanate), [Mn(II)(CF2)3]TBA (TBA = tetrabutylammonium) () and [Mn(II)(DBM)3]TBA (), have been evaluated. At room temperature, the complexes undergo ligand exchange with 4-tert-butyl-pyridine, an additive commonly used in the solar device to reduce charge recombination at the photoanode. An increased device stability was achieved by using the Z907 dye and passivating the photoanode with short chain siloxanes. It was also found that the Mn(ii)/(iii) couple is involved in the dye regeneration process, instead of Mn(iii)/(iv) (E1/2 > 1 V vs. SCE) previously indicated in the literature.