Rita Boaretto

New Components for Dye-Sensitized Solar Cells

Dye-Sensitized Solar Cells (DSSCs) are among the most promising solar energy conversion devices of new generation, since coupling ease of fabrication and low cost offer the possibility of building integration in photovoltaic windows and facades. Although in their earliest configuration these systems are close to commercialization, fundamental studies are still required for developing new molecules and materials with more desirable properties as well as improving our understanding of the fundamental processes at the basis of the functioning of photoactive heterogeneous interfaces. In this contribution, some recent advances, made in the effort of improving DSSC devices by finding alternative materials and configurations, are reviewed.

Photochemistry of the [Fe(CN)5N(O)SR]3- complex : A mechanistic study

Photochemical behaviour of the title complex (RS − = mercaptosuccinate) was defined as photodissociation and photooxidation–

Some aspects of the charge transfer dynamics in nanostructured WO3 films

The photoanodic response of two different types of nanocrystalline WO3 electrodes prepared by following either the sol gel approach or the accelerated anodization route was explored in sulfate containing electrolytes with the aim of exploring the mechanism of charge separation at WO3/electrolyte interfaces. Combined evidence by electrochemical impedance spectroscopy and transient absorption spectroscopy indicates that hole transfer occurs through the valence band and that, under applied bias, the voltage drop involves predominantly the space charge layer of the semiconductor, controlling the photocurrent via potential-induced variations of hole density at the surface of WO3. OH radicals were found among the primary water oxidation intermediates, and are partly responsible for mediated back recombination. The generation of hydroxyl radicals suggests, however, that WO3 based materials can find promising applications in environmental photoremediation under visible light, promoting ˙OH mediated oxidation of impervious contaminants. In principle, the removal of ˙OH by organic scavengers will also optimize the photocurrent generation in photoelectrochemical cells where the generation of hydrogen can be coupled to environmental decontamination.

Generation of [Tp∗Rh(η4-1,3-COD)] (Tp∗ = hydridotris(3,5-dimethyl)pyrazolylborate, 1,3-COD = cyclooctadiene) and its potential in CH bond activation

Photolysis of [Tp∗Rh(η4-1,5-COD)] 1 (Tp∗ = hydridotris(3,5-dimethylpyrazolyl)borate, 1,5-COD = cyclooctadiene) in benzene at 400 nm gives a quantitative yield of the new compound [Tp∗Rh(η4-1,3-COD)] 2. Selected photolysis of 2 at 336 nm can be used to produce (a) hydrido-phenyl-phosphite [Tp∗Rh(H)(C6H5)P(OMe)3], (b) hydrido-carbonyl [Tp∗Rh(H)2(CO)], (c) chelate [Tp∗Rh(C6H5)(CH2CH2COOtBu] when the photoreactions were made in the presence of P(OMe)3, CH3OH and tBu-acrylate, respectively. These results are interpreted in terms of oxidative addition reactions by the reactive intermediates photogenerated in the Rh system 2.

Photochemistry of platinum phosphine complexes. Perspective in CH bond activation

The photochemistry of the diphosphino Pt(II) hydrides [LPtH2] (L=(t-Bu)2P(CH2)2P(t-Bu)2 (7); L=(t-Bu)2P(CH2)3P(t-Bu)2 (8);L=(t-Bu)(Ph)P(CH2)2P(Ph)(t-Bu) (9)) is reported. The primary photoevent is the dissociation of H2 and formation of the 14-e [LPt] species. These coordinatively unsaturated intermediates provide a versatile entry point into the CH bond activation of hydrocarbons. [LPt] reacts with benzene in an oxidative addition reaction to yield [LPt(H)(C6H5)] complexes. The importance of the metal centre and ancillary ligation in the CH bond activation is discussed.

Solar Energy Conversion in Photoelectrochemical Systems

The organization of photoresponsive molecular systems and nano-materials on semiconductor surface holds great potential in the building of solar energy conversion devices where efficient energy conversion results from the optimized cooperation of several subsystems (semiconductor, dye sensitizers, redox mediator, hole transport medium), whose properties can be finely tuned through rational synthetic design. This chapter will review the fundamentals of semiconductor sensitization, a process relying on the quenching by charge transfer of molecular excited states coupled to semiconductor surfaces, and will move on by describing the structural and electronic properties of some of the most successful dye designs, used in conjunction with new electron transfer mediators in liquid electrolytes. From liquid electrolytes, a step forward is made by developing solid state hole conductors, which found their best employment in hybrid junctions with organo-halide lead perovskites, representing, at present, the most promising materials for solar-to-electric power conversion in mesoscopic solar cells. Finally, one of the most challenging tasks which can find solution by exploiting molecular level sensitized materials is discussed in detail through meaningful case studies: the production of solar fuels by photoelectrochemical water splitting.

Dye-sensitized solar cells based on a push-pull zinc phthalocyanine bearing diphenylamine donor groups : computational predictions face experimental reality

Computational studies have suggested that the integration of secondary amine as donor groups in the structure of unsymmetrical zinc phthalocyanine (ZnPc) should have positive effects on photovoltaic performance, once the molecule is integrated as light harvester in dye sensitized solar cells (DSSCs). Aiming at obtaining experimental confirmation, we synthesized a peripherally substituted push-pull ZnPc bearing three electron donating diphenylamine substituents and a carboxylic acid anchoring group and integrated it as sensitizer in TiO2-based DSSCs. Detailed functional characterization of solar energy converting devices resulted in ruling out the original hypothesis. The causes of this discrepancy have been highlighted, leading to a better understanding of the conditions for an effective design of push-pull diarylamino substituted ZnPcs for DSSCs.

Photoelectrochemical Behavior of Electrophoretically Deposited Hematite Thin Films Modified with Ti(IV)

Doping hematite with different elements is a common strategy to improve the electrocatalytic activity towards the water oxidation reaction, although the exact effect of these external agents is not yet clearly understood. Using a feasible electrophoretic procedure, we prepared modified hematite films by introducing in the deposition solution Ti(IV) butoxide. Photoelectrochemical performances of all the modified electrodes were superior to the unmodified one, with a 4-fold increase in the photocurrent at 0.65 V vs. SCE in 0.1 M NaOH (pH 13.3) for the 5% Ti-modified electrode, which was the best performing electrode. Subsequent functionalization with an iron-based catalyst led, at the same potential, to a photocurrent of ca. 1.5 mA·cm−2, one of the highest achieved with materials based on solution processing in the absence of precious elements. AFM, XPS, TEM and XANES analyses revealed the formation of different Ti(IV) oxide phases on the hematite surface, that can reduce surface state recombination and enhance hole injection through local surface field effects, as confirmed by electrochemical impedance analysis.

Photochemistry of μ-hydrido-tetrakis(tertiary phosphine)-diplatinum complexes

Abstract The present work examines the photochemistry of μ-hydrido-tetrakis(ethylphosphine)diplatinum complexes, trans–trans monohydrido-bridged [(PEt 3 ) 2 HPt(μ-H)PtH(PEt 3 ) 2 ][BPh 4 ] ( 1 ) and trans–cis dihydrido-bridged [(PEt 3 ) 2 HPt(μ-H 2 )Pt(PEt 3 ) 2 ][BPh 4 ] ( 2 ). The primary photoprocess of these complexes is homolysis of their Pt–Pt bonds. Interesting consequences of Pt–Pt bond dissociation include cleavage of Pt(μ-H)Pt and Pt(μ-H 2 )Pt yielding the reactive complexes [(PEt 3 ) 2 PtH 2 ] ( 3 ) and [(PEt 3 ) 2 PtH(S)][BPh 4 ] ( 4 ) (S: solvent). Depending on experimental conditions, photoproducts 3 and 4 can undergo a multiplicity of reactions. In acetone photoproducts 3 and 4 undergo a thermal coupling reaction forming the trans–cis isomer 2 . Selective photolysis of 3 and 4 gives elimination of H 2 and solvent with generation of reactive intermediates [(PEt 3 ) 2 Pt] ( 5 ) and [(PEt 3 ) 2 PtH] + ( 6 ). Photogenerated 5 and 6 fragments react cleanly with CO to form 18 electron compounds [(PEt 3 ) 2 Pt(CO) 2 ] ( 7 ) and [(PEt 3 ) 2 Pt(H)(CO)] + ( 8 ). In CH 2 Cl 2 , the photoproducts 5 and 6 could abstract halide from the solvent to form as the only final products [(PEt 3 ) 2 Pt(Cl)CH 2 Cl] ( 9 ) and [(PEt 3 ) 2 Pt(H)Cl] ( 10 ). The photoreactions are interpreted in terms of excited state decay channels.