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1.
Chemistry ; 23(68): 17209-17212, 2017 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-29064135

RESUMO

Methods for effective synthesis for the four possible isomeric 3,9-diphenylullazine carboxaldehydes and reactive halogen intermediates are described. Ullazine donor-acceptor (D-A) dyes were studied using UV/Vis, photoluminescence (PL) spectroscopy and cyclic voltammetry. X-ray single crystal diffraction analysis independently confirmed the structures of two key intermediates. A D-A dye based on ullazine with dihexylmalonate acceptor was tested as a dopant-free hole-transporting material (HTM) in a perovskite solar cell, exhibiting promising power conversion efficiency (PCE) reaching 13.07 %.

2.
Nature ; 538(7626): 463-464, 2016 10 27.
Artigo em Inglês | MEDLINE | ID: mdl-27786213
3.
Chem Commun (Camb) ; 50(75): 10971-4, 2014 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-25093945

RESUMO

Novel star-shaped hole transporting materials with a triazine unit have been synthesized. When the new Triazine-Th-OMeTPA was used as a hole transporting material in perovskite solar cells, the power conversion efficiency reached 12.51% under AM 1.5 G (100 mW cm(-2)) illumination, showing competitive photovoltaic performance with the widely used spiro-OMeTAD based solar cell (13.45%).

4.
ChemSusChem ; 7(10): 2930-8, 2014 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-25146378

RESUMO

Two thiocyanate-free ruthenium(II) sensitizers, TFRS-41 and TFRS-42, with distinctive dialkoxyphenyl thienyl substituents were successfully prepared and tested for potential applications in making dye-sensitized solar cells (DSCs). Subsequent device fabrication was conducted by using a [Co(bpy)3 ](2+/3+) -based (bpy=2,2'-bipyridine) electrolyte, for which the best performance data, namely, JSC =13.11 mA cm(-2) , VOC =862 mV, fill factor=0.771, and η=8.71%, were recorded for the sensitizer TFRS-42 with a 2,6-dialkoxyphenyl substituent under AM 1.5G irradiation. The markedly higher Voc value was confirmed by the longer electron lifetime revealed in transient photovoltage (TPV) measurements versus the TFRS-1 sensitizer. In addition, DFT calculation and detailed first-principles computational analysis were conducted to provide a rationale for the observed trends in their photovoltaic performances and electron lifetimes, with reference to different performances exhibited by three thiocyanate-free sensitizers, TFRS-1, TFRS-41 and TFRS-42, versus Z907 reference. Through the proper control of peripheral substituents, the thiocyanate-free ruthenium(II)-based DSC sensitizers can positively influence the performances of DSCs, with better light-harvesting capability and suppressed charge recombination, for DSC cells fabricated by using a [Co(bpy)3 ](2+/3+) -based electrolyte.


Assuntos
Azóis/síntese química , Fontes de Energia Elétrica , Compostos Organometálicos/síntese química , Piridinas/síntese química , Rutênio/química , Energia Solar , Azóis/química , Técnicas Eletroquímicas , Espectroscopia de Ressonância Magnética , Simulação de Dinâmica Molecular , Compostos Organometálicos/química , Piridinas/química , Espectrometria de Massas de Bombardeamento Rápido de Átomos
5.
Inorg Chem ; 53(11): 5417-9, 2014 Jun 02.
Artigo em Inglês | MEDLINE | ID: mdl-24823893

RESUMO

Coordination of bidentate 5-pentafluorophenyldipyrrinate (pfpdp) or 5-(2-thienyl)dipyrrinate (2-tdp) to a Ru(II) center bearing 2,2':6',2″-terpyridine-4,4',4″-tricarboxylate (tctpy) and a NCS(-) ligand results in strongly light-absorbing complexes [Ru(tctpy)(L)(NCS)] (L = pfpdp or 2-tdp). Anchored to a mesoporous TiO2 electrode, these complexes afford a photoaction spectral response at wavelengths of up to 950 nm, one of the most red-shifted values reported to date for molecular dyes in the dye-sensitized solar cell (DSSC).

6.
Chemphyschem ; 15(6): 1033-6, 2014 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-24590767

RESUMO

A new phthalocyanine (Pc) bearing bulky peripheral substituents and a carboxylic anchoring group directly attached to the macrocycle has been prepared and used as a sensitizer in DSSCs, reaching 5.57% power conversion efficiency. In addition, an enhanced performance for the TT40 dye, previously reported by us, was achieved in optimized devices, obtaining a new record efficiency with Pc-sensitized cells.

7.
ACS Nano ; 8(3): 2261-8, 2014 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-24552648

RESUMO

Mesoporous TiO2 nanoparticle films are used as photoanodes for high-efficiency dye-sensitized solar cells (DSCs). In spite of excellent photovoltaic power conversion efficiencies (PCEs) displayed by titanium dioxide nanoparticle structures, the transport rate of electrons is known to be low due to low electron mobility. So the alternate oxides, including ZnO, that possesses high electron mobility are being investigated as potential candidates for photoanodes. However, the PCE with ZnO is still lower than with TiO2, and this is typically attributed to the low internal surface area. In this work, we attempt to make a one-to-one comparison of the photovoltaic performance and the electron transfer dynamics involved in DSCs, with ZnO and TiO2 as photoanodes. Previously such comparative investigations were hampered due to the morphological differences (internal surface area, pore diameter, porosity) that exist between zinc oxide and titanium dioxide films. We circumvent this issue by depositing different thicknesses of these oxides, by atomic layer deposition (ALD), on an arbitrary mesoporous insulating template and subsequently using them as photoanodes. Our results reveal that at an optimal thickness ZnO exhibits photovoltaic performances similar to TiO2, but the internal electron transfer properties differ. The higher photogenerated electron transport rate contributed to the performances of ZnO, but in the case of TiO2, it is the low recombination rate, higher dye loading, and fast electron injection.

8.
Angew Chem Int Ed Engl ; 53(12): 3151-7, 2014 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-24554633

RESUMO

Hybrid organic-inorganic lead halide perovskite APbX3 pigments, such as methylammonium lead iodide, have recently emerged as excellent light harvesters in solid-state mesoscopic solar cells. An important target for the further improvement of the performance of perovskite-based photovoltaics is to extend their optical-absorption onset further into the red to enhance solar-light harvesting. Herein, we show that this goal can be reached by using a mixture of formamidinium (HN=CHNH3 (+), FA) and methylammonium (CH3 NH3 (+), MA) cations in the A position of the APbI3 perovskite structure. This combination leads to an enhanced short-circuit current and thus superior devices to those based on only CH3 NH3 (+). This concept has not been applied previously in perovskite-based solar cells. It shows great potential as a versatile tool to tune the structural, electrical, and optoelectronic properties of the light-harvesting materials.

9.
Nano Lett ; 14(3): 1190-5, 2014 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-24524200

RESUMO

We present a photoanode for dye-sensitized solar cell (DSC) based on ZnO nanoshell deposited by atomic layer deposition at 150 °C on a mesoporous insulating template. An ultrathin layer of ZnO between 3 and 6 nm, which exhibits quantum confinement effect, is found to be sufficient to transport the photogenerated electrons to the external contacts and exhibits near-unity collection efficiency. A 6 nm ZnO nanoshell on a 2.5 µm mesoporous nanoparticle Al2O3 template yields photovoltaic power conversion efficiency (PCE) of 4.2% in liquid DSC. Perovskite absorber (CH3NH3PbI3) based solid state solar cells made with similar ZnO nanostructures lead to a high PCE of 7%.

10.
Chemistry ; 20(7): 2016-21, 2014 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-24443172

RESUMO

A series of subphthalocyanines (SubPcs) bearing a carboxylic acid group either at the peripheral or axial position have been designed and synthesized to investigate the influence of the COOH group positions on the dye-sensitized solar cell (DSSC) performance. The DSSC devices based on SubPcs with axially substituted carboxylic acid groups showed low photovoltaic performance, whereas peripherally substituted one exhibited higher power conversion efficiency owing to improved injection from LUMO of SubPcs to the TiO2 conduction band.

11.
Dalton Trans ; 43(7): 2726-32, 2014 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-24366343

RESUMO

A new Ru(II) dye, Ru(L1)(L2) (NCS)2, L1 = (4-(5-hexylthiophen-2-yl)-4'(4-carboxyl-phenyl 2,2'-bipyridine) and L2 = (4-4'-dicarboxy-2,2'-bipyridine), labelled MC112, based on a dissymmetric bipyridine ligand for improved interfacial and optical properties, was synthesized and used in DSCs, yielding photovoltaic efficiencies of 7.6% under standard AM 1.5 sunlight and an excellent device stability. Increased light harvesting and IPCE maximum were observed with MC112 compared to the prototypical homoleptic N719 dye, due to the functionalized bipyridyne ligand acting as an antenna. In addition, the mixed bipyridyne ligand allowed MC112 binding to TiO2 to occur via three anchoring carboxylic groups, thus exhibiting similar interfacial properties to those of the N719 dye. DFT/TDDFT calculations were performed on the new dye, both in solution and adsorbed on a TiO2 surface model, revealing that the peculiar photovoltaic properties of the MC112 dye are related to its anchoring mode. The new design rule thus allows us to engineer both light-harvesting and interfacial properties in the same dye.

12.
Dalton Trans ; 43(15): 5667-79, 2014 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-24345847

RESUMO

While phosphorescent cyclometalated iridium(iii) complexes have been widely studied, only correlations between oxidation potential EOX and Hammett constant σ, and between the redox gap (ΔEREDOX = EOX-ERED) and emission or absorption wavelength (λabs, λem) have been reported. We present now a quantitative model based on Hammett parameters that rationalizes the effect of the substituents on the properties of cyclometalated iridium(iii) complexes. This simple model allows predicting the apparent redox potentials as well as the electrochemical gap of homoleptic complexes based on phenylpyridine ligands with good accuracy. In particular, the model accounts for the unequal effect of the substituents on both the HOMO and the LUMO energy levels. Consequently, the model is used to anticipate the emission maxima of the corresponding complexes with improved reliability. We demonstrate in a series of phenylpyridine emitters that electron-donating groups can effectively replace electron-withdrawing substituents on the orthometallated phenyl to induce a blue shift of the emission. This result is in contrast with the common approach that uses fluorine to blue shift the emission maximum. Finally, as a proof of concept, we used electron-donating substituents to design a new fluorine-free complex, referred to as EB343, matching the various properties, namely oxidation and reduction potentials, electrochemical gap and emission profile, of the standard sky-blue emitter FIrPic.

13.
Nanoscale ; 6(3): 1508-14, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24322660

RESUMO

We report the use of Y(3+)-substituted TiO2 (0.5%Y-TiO2) in solid-state mesoscopic solar cells, consisting of CH3NH3PbI3 as the light harvester and spiro-OMeTAD as the hole transport material. A power conversion efficiency of 11.2% under simulated AM 1.5 full sun illumination was measured. A 15% improvement in the short-circuit current density was obtained compared with pure TiO2, due to the effect of Y(3+) on the dimensions of perovskite nanoparticles formed on the semiconductor surface, showing that the surface modification of the semiconductor is an effective way to improve the light harvesters' morphology and electron transfer properties in the solid-state mesoscopic solar cells.

14.
Nature ; 499(7458): 316-9, 2013 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-23842493

RESUMO

Following pioneering work, solution-processable organic-inorganic hybrid perovskites-such as CH3NH3PbX3 (X = Cl, Br, I)-have attracted attention as light-harvesting materials for mesoscopic solar cells. So far, the perovskite pigment has been deposited in a single step onto mesoporous metal oxide films using a mixture of PbX2 and CH3NH3X in a common solvent. However, the uncontrolled precipitation of the perovskite produces large morphological variations, resulting in a wide spread of photovoltaic performance in the resulting devices, which hampers the prospects for practical applications. Here we describe a sequential deposition method for the formation of the perovskite pigment within the porous metal oxide film. PbI2 is first introduced from solution into a nanoporous titanium dioxide film and subsequently transformed into the perovskite by exposing it to a solution of CH3NH3I. We find that the conversion occurs within the nanoporous host as soon as the two components come into contact, permitting much better control over the perovskite morphology than is possible with the previously employed route. Using this technique for the fabrication of solid-state mesoscopic solar cells greatly increases the reproducibility of their performance and allows us to achieve a power conversion efficiency of approximately 15 per cent (measured under standard AM1.5G test conditions on solar zenith angle, solar light intensity and cell temperature). This two-step method should provide new opportunities for the fabrication of solution-processed photovoltaic cells with unprecedented power conversion efficiencies and high stability equal to or even greater than those of today's best thin-film photovoltaic devices.

15.
ACS Appl Mater Interfaces ; 5(8): 3487-93, 2013 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-23506374

RESUMO

Low-temperature processing of dye-sensitized solar cells (DSCs) is crucial to enable commercialization with low-cost, plastic substrates. Prior studies have focused on mechanical compression of premade particles on plastic or glass substrates; however, this did not yield sufficient interconnections for good carrier transport. Furthermore, such compression can lead to more heterogeneous porosity. To circumvent these problems, we have developed a low-temperature processing route for photoanodes where crystalline TiO2 is deposited onto well-defined, mesoporous templates. The TiO2 is grown by atomic layer deposition (ALD), and the crystalline films are achieved at a growth temperature of 200 °C. The ALD TiO2 thickness was systematically studied in terms of charge transport and performance to lead to optimized photovoltaic performance. We found that a 15 nm TiO2 overlayer on an 8 µm thick SiO2 film leads to a high power conversion efficiency of 7.1% with the state-of-the-art zinc porphyrin sensitizer and cobalt bipyridine redox mediator.

16.
Angew Chem Int Ed Engl ; 52(1): 376-80, 2013 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-22927088

RESUMO

Positive to the core: ullazine has both strong electron-donating and weak accepting properties. This heterocycle was incorporated into sensitizers for dye-sensitized solar cells (DSCs). One of these sensitizers demonstrated strong light absorption across the UV/Vis region. The corresponding DSC device has a maximum IPCE of 95 % at 520 nm, with a power conversion efficiency of 8.4 %.

17.
Dalton Trans ; 42(4): 1073-87, 2013 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-23114723

RESUMO

Four new heteroleptic iridium(III) complexes in the family [Ir(dfppz)(2)(N^N)](+), where Hdfppz = 1-(2,4-difluorophenyl)-1H-pyrazole and N^N = 6-phenyl-2,2'-bipyridine (1), 4,4'-(di-tert-butyl)-6-phenyl-2,2'-bipyridine (2), 4,4'-(di-tert-butyl)-6,6'-diphenyl-2,2'-bipyridine (3) and 4,4'-bis(dimethylamino)-2,2'-bipyridine (4), have been synthesized as the hexafluoridophosphate salts and fully characterized. Single crystal structures of ligand 3 and the precursor [Ir(2)(dfppz)(4)(µ-Cl)(2)] have been determined, along with the structures of the complexes 4{[Ir(dfppz)(2)(1)][PF(6)]}·3CH(2)Cl(2), [Ir(dfppz)(2)(3)][PF(6)]·CH(2)Cl(2) and [Ir(dfppz)(2)(4)][PF(6)]·CH(2)Cl(2). The role of inter- and intramolecular face-to-face π-stacking in the solid state is discussed. In the [Ir(dfppz)(2)(N^N)](+) (N^N = 1-3) cations, the phenyl substituent in ligands 1, 2 or 3 undergoes hindered rotation on the NMR timescale at 298 K in solution and the systems have been studied by variable temperature NMR spectroscopy. Acetonitrile solutions of [Ir(dfppz)(2)(N^N)][PF(6)] (N^N = 1-3) exhibit similar absorption spectra arising from ligand-based transitions; absorption intensity is enhanced on going to [Ir(dfppz)(2)(4)][PF(6)] and the spectrum extends further into the visible region. Acetonitrile solutions of the complexes are blue emitters with λ(em) = 517, 505, 501 and 493 nm for N^N = 1, 2, 3 and 4, respectively (λ(exc) = 280-310 nm). The redox behaviours of [Ir(dfppz)(2)(N^N)][PF(6)] (N^N = 1-3) are similar, and the introduction of the electron-donating NMe(2) substituents onto the N^N ligand shifts the metal-centred oxidation to less positive potentials. Theoretical calculations predict a mixed metal-to-ligand/ligand-to-ligand charge transfer (MLCT/LLCT) character for the emitting triplet state in agreement with the broad and unstructured character of the emission bands. The NMe(2) substituents enlarge the HOMO-LUMO gap and blue-shifts the emission of [Ir(dfppz)(2)(4)](+) that is centred on the ancillary ligand. These complexes, when processed into a thin film and sandwiched between two electrodes, lead to very low voltage operating electroluminescent devices. No additional components are needed, which demonstrates their electron and hole transport abilities in conjunction with the luminescent properties.

18.
Chemistry ; 19(5): 1819-27, 2013 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-23255425

RESUMO

A series of squaraine-based sensitizers with various π bridges and anchors were prepared and examined in dye-sensitized solar cells. The carboxylic anchor group was attached onto a squaraine dye through π bridges with and without an ethynyl spacer. DFT studies indicate that the LUMO is delocalized throughout the dyes, whilst the HOMO resides on the squaraine core. The dye that incorporates a 4,4-di-n-hexyl-cyclopentadithiophene group that is directly attached onto the π bridge, JD10, exhibits the highest power conversion efficiency in a DSC; this result is attributed, in part, to the deaggregative properties that are associated with the gem-di-n-hexyl substituents, which extend above and below the π-conjugated dye plane. Dye JD10 demonstrates a power-conversion efficiency of 7.3% for liquid-electrolyte dye-sensitized solar cells and 7.9% for cells that are co-sensitized by another metal-free dye, D35, which substantially exceed the performance of any previously tested squaraine sensitizer. A panchromatic incident-photon-to-current-conversion efficiency curve is realized for this dye with an excellent short-circuit current of 18.0 mA cm(-2). This current is higher than that seen for other squaraine dyes, partially owing to a high molar absorptivity of >5,000 M(-1) cm(-1) from 400 nm to the long-wavelength onset of 724 nm for dye JD10.

19.
J Am Chem Soc ; 134(47): 19438-53, 2012 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-23113640

RESUMO

We report a combined experimental and computational investigation to understand the nature of the interactions between cobalt redox mediators and TiO(2) surfaces sensitized by ruthenium and organic dyes, and their impact on the performance of the corresponding dye-sensitized solar cells (DSSCs). We focus on different ruthenium dyes and fully organic dyes, to understand the dramatic loss of efficiency observed for the prototype Ru(II) N719 dye in conjunction with cobalt electrolytes. Both N719- and Z907-based DSSCs showed an increased lifetime in iodine-based electrolyte compared to the cobalt-based redox shuttle, while the organic D21L6 and D25L6 dyes, endowed with long alkoxy chains, show no significant change in the electron lifetime regardless of employed electrolyte and deliver a high photovoltaic efficiency of 6.5% with a cobalt electrolyte. Ab initio molecular dynamics simulations show the formation of a complex between the cobalt electrolyte and the surface-adsorbed ruthenium dye, which brings the [Co(bpy)(3)](3+) species into contact with the TiO(2) surface. This translates into a high probability of intercepting TiO(2)-injected electrons by the oxidized [Co(bpy)(3)](3+) species, lying close to the N719-sensitized TiO(2) surface. Investigation of the dye regeneration mechanism by the cobalt electrolyte in the Marcus theory framework led to substantially different reorganization energies for the high-spin (HS) and low-spin (LS) reaction pathways. Our calculated reorganization energies for the LS pathways are in excellent agreement with recent data for a series of cobalt complexes, lending support to the proposed regeneration pathway. Finally, we systematically investigate a series of Co(II)/Co(III) complexes to gauge the impact of ligand substitution and of metal coordination (tris-bidentate vs bis-tridentate) on the HS/LS energy difference and reorganization energies. Our results allow us to trace structure/property relations required for further development of cobalt electrolytes for DSSCs.

20.
Chem Commun (Camb) ; 48(87): 10727-9, 2012 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-23022986

RESUMO

A novel, asymmetric DPP bridge/core was synthesized and tested in DSC devices. By desymmetrising the DPP core/bridge, a remarkable IPCE of >80% and a maximum power conversion efficiency of 7.7% were achieved. With the use of a wide-bandgap co-sensitizer, 8.6% PCE was realized under standard AM1.5G sunlight.


Assuntos
Corantes/química , Fontes de Energia Elétrica , Pirróis/química , Energia Solar , Corantes/síntese química , Estrutura Molecular , Pirróis/síntese química
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