Porphyrin Dyes Research Articles

Enhanced Electron Lifetimes in Dye-Sensitized Solar Cells Using a Dichromophoric Porphyrin: The Utility of Intermolecular Forces.

Electron lifetimes in dye-sensitized solar cells employing a porphyrin dye, an organic dye, a 1:1 mixture of the two dyes, and a dichromophoric dye design consisting of the two dyes using a nonconjugated linker were measured, suggesting that the dispersion force of the organic dyes has a significant detrimental effect on the electron lifetime and that the dichromophoric design can be utilized to control the effect of the dispersion force.

Photoinjection of High Potential Holes into Cu5Ta11O30 Nanoparticles by Porphyrin Dyes

Excited-state hole injection into the valence band of Cu5Ta11O30 nanoparticles (NP-Cu5Ta11O30) was investigated through sensitization with zinc porphyrin dyes using simulated solar irradiance. The Cu5Ta11O30 nanoparticles were prepared by a flux-mediated synthesis and found to have an average particle size of ∼10–15 nm by DLS and TEM. The zinc 4-(10,15,20-tris(4-pyridinyl)-porphin-5-yl)phenylphosphonic acid (D1) and its analogue, in which the pyridine groups are methylated (D2), were synthesized and found to have excited-state reduction potentials appropriate for p-type dye sensitization of the nanoparticles. The dye-sensitized NP-Cu5Ta11O30 exhibited fluorescence quenching consistent with electron transfer from the NP-Cu5Ta11O30 to the dye; forward and recombination rates were obtained by transient absorption measurements. Hole injection times of 8 ps and <100 fs were observed for D1 and D2, respectively. Nanoparticulate films of Cu5Ta11O30 were prepared and evaluated in dye-sensitized solar cells under simulated solar irradiance (AM 1.5 G, 100 mW/cm2). Measurable photocurrents and open-circuit potentials (Voc) of 200 and 110 mV were observed using D1 and D2, respectively.

D–π–A system based on zinc porphyrin dyes for dye-sensitized solar cells: Combined experimental and DFT–TDDFT study

A series of four new porphyrin-furan dyads were designed and synthesized by having anchoring group either at meso-phenyl or pyrrole-β position of a zinc porphyrin based on donor–π–acceptor (D–π–A) approach. The porphyrin macrocycle acts as donor, furan hetero cycle acts as π-spacer and either cyanoacetic acid or malonic acid group acts as acceptor. These dyads were fully characterized by UV–Visible, 1H NMR, MALDI-MS and fluorescence spectroscopies and cyclic voltammetry. Both of the observed and TD-DFT simulated UV–Vis spectra has strong correlation which validate and confirm the synthesized dyads and theoretical method for this type of compounds. Both soret and Q-bands are red shifted in the case of pyrrole-β substituted dyads. The redox potentials of all four dyads are not altered in comparison with their individual constituents. The dyads were tested in dye sensitized solar cells and found pyrrole-β substituted zinc porphyrins are showing better performance in comparison with the corresponding meso-phenyl dyads. Optical band gap, Natural bonding, and Molecular bonding orbital (HOMO–LUMO) analysis are in favour of pyrrole-β substituted zinc porphyrins contrast to meso-phenyl dyads.

Synthesis and Characterization of Schiff Base-Substituted Zinc Porphyrin Dye for Sensitized Solar Cells

Synthesis and Characterization of Schiff Base-Substituted Zinc Porphyrin Dye for Sensitized Solar Cells

Strategy for tuning the photophysical properties of photosensitizers for use in photodynamic therapy.

A novel approach for tuning spectral properties, as well as minimizing aggregation, in zinc porphyrin and zinc phthalocyanine-based compounds is presented. Particular emphasis is placed on use of these compounds as photosensitizers in photodynamic therapy (PDT). To accomplish this aim, a bulky hydrophobic cation, trihexyltetradecylphosphonium, is paired with anionic porphyrin and phthalocyanine dyes to produce a group of uniform materials based on organic salts (GUMBOS) that absorb at longer wavelengths with high molar absorptivity and high photostability. Nanoparticles derived from these GUMBOS possess positively charged surfaces with high zeta potential values, which are highly desirable for PDT. Upon irradiation at longer wavelengths, these GUMBOS produced singlet oxygen with greater efficiency as compared to the respective parent dyes.

Sn(IV) Metalloporphyrin/Co(III) Complex: An All-Abundant-Element System for the Photocatalytic Production of H2 in Aqueous Solution.

A new, molecular system for the light-driven production of hydrogen in aqueous solution was developed by combining a water-soluble tin porphyrin ([Sn(IV)Cl2TPPC], A) acting as photosensitizer with a cobalt-based proton-reduction catalyst ([Co(III)Cl(dmgH)2(py)], C). Under visible light illumination and with triethanolamine (TEOA) as electron source, the system evolves H2 for hours and is clearly catalytic in both dye and catalyst. A detailed analysis of the relevant redox potentials in combination with time-resolved spectroscopy resulted in the development of a Z-scheme type model for the flow of electrons in this system. Key intermediates of the proposed mechanism for the pathway leading to H2 are the porphyrin dye's highly oxidizing singlet excited state (1)A* (E ∼ +1.3 V vs NHE), its strongly reducing isobacteriochlorin analogue (E ∼ +0.95 V), and the Co(I) form of C (E ∼ -0.8 V), acting as catalyst for H2 formation. Among other results, the suggested reaction sequence is supported by the detection of a shortened excited-state lifetime for singlet (1)A* (τ ∼ 1.75 ns) in the presence of TEOA and the ultraviolet-visible detection of the Sn(IV) isobacteriochlorin intermediate at λ = 610 nm. Thus, a molecular, conceptually biomimetic, and precious-metal-free reaction chain was found which photocatalytically generates H2 in a 100% aqueous system from an electron donor with a high oxidation potential (E(TEOA) ∼ +1.1 V). On the other hand, at identical conditions, this photoreaction chain yields H2 markedly slower than a system using the photosensitizer [Re(I)(CO)3(bpy) (py)](+), probably due to the much longer excited-state lifetime (τ ∼ 120 ns) of the rhenium dye and better electron-transfer rates caused by its simple single-electron photoreduction chemistry.

Efficient co-sensitization of dye-sensitized solar cells by novel porphyrin/triazine dye and tertiary aryl-amine organic dye

A novel porphyrin dye ZnP-triazine-(gly)2, consisting of a zinc-metallated porphyrin unit covalently linked through its peripheral aryl-amino group with a 1,3,5-triazine group which is functionalized by two carboxylic acid groups of glycine moieties, has been synthesized. Photophysical and electrochemical measurements, as well as theoretical DFT calculations, suggest that the compound exhibits appropriate light absorption characteristics and frontier molecular orbital levels for use as sensitizer in dye-sensitized solar cells (DSSCs). The ZnP-triazine-(gly)2 based solar cell was found to exhibit a power conversion efficiency (PCE) value of 4.72%. A significant improvement of the overall photovoltaic efficiency of the solar cell was achieved up to 7.34% upon co-sensitization with a tertiary aryl-amine D with two ethynyl-pyridine substituents and cyano-acetic acid anchoring group, which exhibits complementary light absorption characteristics with the porphyrin dye. The higher PCE value of the co-sensitized solar cell is attributed to its enhanced short circuit current (Jsc), which is due to improved light harvesting efficiency, reduced porphyrin aggregation, and faster electron injection and charge collection, as well as its enhanced open circuit voltage (Voc), which is due to increased electron density in the TiO2 conduction band of the photoanode. These results are in accordance with electrochemical impedance spectra (EIS) of the solar cells, which revealed higher charge recombination resistance (Rrec), longer electron lifetime (τe), and shorter electron transport time (τd) for the co-sensitized solar cell.

Porphyrin Sensitizers Bearing a Pyridine-Type Anchoring Group for Dye-Sensitized Solar Cells.

Three novel efficient donor-acceptor porphyrins, MH1-MH3, with a pyridine-type acceptor and anchoring group were synthesized and their optical, electrochemical, and photovoltaic properties investigated. Replacing the commonly used 4-carboxyphenyl anchoring group with 2-carboxypyridine, 2-pyridone, and pyridine did not significantly change the absorption and electrochemical properties of the porphyrin dyes. These new porphyrin dyes MH show power conversion efficiencies of 8.3%, 8.5%, and 8.2%, which are comparable to that of the benchmark YD2-o-C8 (η=8.25%) under similar conditions. It was demonstrated that 2-carboxypyridine is an efficient and stable anchoring group as MH1 and showed better cell performance and long-term stability than YD2-o-C8 under light soaking conditions.

Wearable System for Monitoring of Oxygen Concentration in Breath Based on Optical Sensor

This paper reports the development of a compact, portable prototype for the determination of gaseous oxygen in breath. This system is fully wearable, it can be worn by the user as an armband where the electronics are placed, i.e., connected to a mouthpiece where the breath is sensed. The prototype is based on an optical luminescent sensor consisting of a stabilized porphyrin dye directly deposited onto a color detector. The sensor response, when it is optically excited, is quenched by the surrounding oxygen. The intensity of the generated luminescence is registered by means of a digital color detector whose output data correspond to the coordinates of the RGB color space. For this particular optical sensor, the red coordinate is directly related to the concentration of O2, and it is sent to a remote device such as a smartphone or tablet by a Bluetooth link. An application for Android operative system has also been developed for data visualization and analysis. Employing this novel system, a high resolution in the range of few parts per billion in the determination of oxygen can be achieved.

Molecular engineering of organic dyes with a hole-extending donor tail for efficient all-solid-state dye-sensitized solar cells.

We report a new concept for the design of metal-free organic dyes (OD5-OD9) with an extended donor-π-acceptor (D-π-A) molecular framework, in which the donor terminal unit is attached by a hole-extending side chain to retard back electron transfer and charge recombination; the π-bridge component contains varied thiophene-based substituents to enhance the light-harvesting ability of the device. The best dye (OD9) has a D-A-π-A configuration with the hexyloxyphenylthiophene (HPT) side chain as a hole-extension component and a benzothiadiazole (BTD) internal acceptor as a π-extension component. The co-sensitization of OD9 with the new porphyrin dye LW24 enhanced the light-harvesting ability to 800 nm; thus, a power conversion efficiency 5.5 % was achieved. Photoinduced absorption (PIA) and transient absorption spectral (TAS) techniques were applied to account for the observed trend of the open-circuit voltage (VOC ) of the devices. This work provides insights into the molecular design, photovoltaic performance, and kinetics of charge recombination.

2-Ethynyl-6-methylthieno[3,2-b]thiophene as an efficient π spacer for porphyrin-based dyes

In this study, three donor-π-acceptor (D-π-A) type unsymmetrical porphyrin-based dyes have been designed and synthesized for dye-sensitized solar cells (DSSCs). The photophysical, electrochemical and photovoltaic properties of the dyes were successfully adjusted by using functionalized arylamines (triphenylamine or N, N-dimethyl-4-(acetylene)-aniline) as donor, porphyrin derivatives as conjugated π bridge, ethynyl-thiophene or ethynyl-thiophthene as π spacer and carboxylic acid as anchor group. Compared with the dye containing ethynyl-thiophene as π spacer, the dyes containing 2-ethynyl-6-methylthieno[3,2-b]thiophene as π spacer between the porphyrin macrocycle and the carboxylic acid anchoring group show broadened absorption spectra on TiO2 films and red-shifted absorption spectra in solution. The dye based on triphenylamine and 2-ethynyl-6-methylthieno[3,2-b]thiophene exhibited a power conversion efficiency (PCE) of 4.53% under simulated air mass 1.5 global sunlight. These results indicate that the introduction of 2-ethynyl-6-methylthieno[3,2-b]thiophene in the meso-positions of porphyrin dyes is an effective approach to improve the photovoltaic performance.

Importance of the Reorganization Energy Barrier in Computational Design of Porphyrin-Based Solar Cells with Cobalt-Based Redox Mediators

The shift from iodide-based redox mediators in dye-sensitized solar cells toward octahedral cobalt complexes has led to a significant increase in the efficiency. However, due to the nature of this type of complexes the driving force required for the regeneration of the dye is very high, and this limits the achievable efficiency. Here we show that the large driving force is a direct consequence of the large reorganization energy of the dye regeneration reaction. The reorganization energies for charge transfer between a simple zinc porphyrin dye and two popular cobalt-based redox mediators is calculated using ab initio molecular dynamics with explicit solvent. These results are then combined with a Marcus-based extrapolation scheme to obtain the reorganization energies of more than 5000 porphyrin-based dyes. We propose a scheme for scoring the performance of the porphyrin dyes, which is able to identify already known high-performance dyes in addition to a number of even better candidates. Our analysis shows that the large internal reorganization energy of the Co-based redox mediators is an obstacle for achieving higher efficiencies.

In situ functionalization of gallium nitride powder with a porphyrin dye

Abstract

Introduction of carboxylic ester and acid functionalities to meso-tetrakis(pentafluorophenyl)porphyrin and their limited electronic effects on the chromophore

Alkyl- or aryl-carboxylic acid-functionalized porphyrinic dyes are sought after because of their propensity to adhere strongly to many metal oxide surfaces as required for their application as, for instance, sensitizers in dye-sensitized solar cells (DSSCs), in air purification, or chemosensing systems. The SNAr reaction of the pentafluorophenyl group is a versatile method to introduce functionality into meso-pentafluorophenyl-substituted porphyrins. The conditions to introduce one through four alkyl- or aryl-carboxyl functionalities using mercaptopropionate or 3,4-dihydroxybenzoate esters, respectively, are explored, and the regioisomeric products are spectroscopically characterized. Their saponification to the corresponding carboxylic acids was studied. By experimental determination of their optical properties (absorption and emission spectroscopy) and their frontier orbital positions by cyclic voltammetry, we demonstrate the minimal electronic influence this derivatization method has on the chromophore.

Co-sensitization of free-base and zinc porphyrins: An effective approach to improve the photon-to-current conversion efficiency of dye-sensitized solar cells

Co-sensitization of two or more sensitizers with complementary absorption profiles had been utilized as an imperative tool to achieve panchromatic sensitization in dye-sensitized solar cells. The highly efficient dye-sensitized solar cells consist of a co-sensitization system comprising of a mixture of porphyrin and organic dye. We have prepared four novel free-base and zinc porphyrins in minimum steps and examined their individual as well as co-sensitized performance in dye-sensitized solar cells. The UV-visible spectrum suggests that upon zinc insertion the absorption wavelength is red-shifted by 10 nm in both Soret and Q-band region. The density functional theory (DFT) calculations revealed that the presence of an electron withdrawing cyanoacrylic acid as the anchoring group has pronounced effect on the charge distribution. IPCE spectra suggest that the co-sensitization of a free-base porphyrin with a zinc porphyrin resulted in panchromatic absorption in whole visible region. The device made with Mix-2, which is composed from the free-base porphyrin N4CN and the zinc porphyrin N4ZnCN gave the best performance with an overall photon-to-current conversion efficiency of 4.18%, with Jsc of 10.4 mA.cm-2, Voc of 0.56 V and fill factor of 72%.

Insight into D-A-π-A Structured Sensitizers: A Promising Route to Highly Efficient and Stable Dye-Sensitized Solar Cells.

The dye-sensitized solar cell (DSSC) is one of the most promising photovoltaic technologies with potential of low cost, light weight, and good flexibility. The practical application of DSSCs requires further improvement in power conversion efficiency and long-term stability. Recently, significant progress has been witnessed in DSSC research owing to the novel concept of the D-A-π-A motif for the molecular engineering of organic photosensitizers. New organic and porphyrin dyes based on the D-A-π-A motif can not only enhance photovoltaic performance, but also improve durability in DSSC applications. This Spotlight on Applications highlights recent advances in the D-A-π-A-based photosensitizers, specifically focusing on the mechanism of efficiency and stability enhancements. Also, we find insight into the additional acceptor as well as the trade-off of long wavelength response. The basic principles are involved in molecular engineering of efficient D-A-π-A sensitizers, providing a clear road map showing how to modulate the energy bands, rationally extending the response wavelength, and optimizing photovoltaic efficiency step by step.

Charge Generation, Regeneration and Recombination in Di-Chromophoric Carbazole-Thiophene-Porphyrin-Sensitised Solar Cells

Porphyrins are among the best performing dyes for their application in dye-sensitized solar cells. However, light harvesting efficiencies between the Soret and Q bands of most simple porphyrins are limited, especially when thin electrodes or electrodes with low surface area are used. Filling the absorption gap is an important objective to further enhance their efficiency, in addition to extending their absorption band edge to better match the solar spectrum. In this work, the absorption gap between the Soret and Q bands is filled using a multi-chromophoric approach following the synthetic strategy we have developed earlier (J. Am. Chem. Soc. 2009, 131, 15621-15623; J. Mater. Chem. A 2014, 2, 16963-16977). Three new porphyrin dyes with carbazole-fused thiophene chromophores attached to the porphyrin core using a non-conjugated phenylethenyl linker are synthesised. When attached to TiO2, an almost complete filling of the absorption gap within the 450 nm to 500 nm is achieved, which leads to doubling of the short circuit current density using the Co2+ / Co3+ electrolyte. In addition, the electron lifetime has significantly improved contributing to increased power conversion efficiency of 4.7%. Particularly significant result is the nearly 100% absorbed photon to collected electron efficiency at wavelengths dominated by the side chain absorption, suggesting the promise of the multi-chromophoric dye design using the non-conjugated approach. Detailed transient absorption and spectro-electrochemical investigations reveal a significant acceleration of dye cation regeneration kinetics in carbazole-porphyrin dyads attached to TiO2. This is attributed to a picosecond to microsecond intramolecular hole transfer from the porphyrin cation to carbazole, followed by a fast reduction of the carbazole cation by the electron donor redox mediator dissolved in the electrolyte. Such increase of the turnover rates without affecting the final electrochemical potential of the photo-generated species is promising for a variety of photo-electrochemical energy conversion processes, including solar cells and solar fuels.

Porphyrins As Excellent Sensitizers for Dye-Sensitized Solar Cells

Recently we have developed aromatic ring-fused, unsymmetrically pi-elongated porphyrins (i.e., naphthalene-fused and quinoxaline-fused porphyrins) that showed broadened, and red-shifted light absorption properties compared to the corresponding porphyrin references, resulting in the power conversion efficiencies of 4.1% and 6.3%, respectively. As demonstrated for other sensitizers in DSSCs, introduction of both electron-donating and electron-withdrawing substituents to a core of pi system would be appealing for the modulation of the light-harvesting properties of sensitizers. In this talk I will present our recent advance in porphyrin-sensitized solar cells.1-10 In particular, I will focus on novel push-pull porphyrins for porphyrin-sensitized solar cells.1-10 For instance, we synthesized for the first time a push-pull porphyrin dye bearing two diarylamino groups and two carboxyphenylethynyl groups as electron-donating and electron-withdrawing anchoring groups, respectively. The absorption spectrum displayed broad and red-shifted absorption, achieving panchromic light-harvesting in visible and NIR regions. Introduction of multiple push-pull groups into meso-positions is a promising strategy for the rational design of porphyrin sensitizers for light-harvesting applications. The preliminary photovoltaic performance is moderate (3.0%), but the extensive photocurrent generation matches with the excellent light-harvesting ability. Further modulation of the photovoltaic properties of porphyrin DSSCs will be possible by suitable selection of electron-donating and electron-withdrawing groups as well as introduction of the substituents into the porphyrin core. [1] H. Imahori, T. Umeyama, and S. Ito, Acc. Chem. Res. 42, 1809 (2009). [2] H. Imahori, S. Kang, H. Hayashi, M. Haruta, H. Kurata, S. Isoda, S. E. Canton, Y. Infahsaeng, A. Kathiravan, T. Pascher, P. Chabera, A. P. Yartsev, and V. Sundström, J. Phys. Chem. A, 115, 3679 (2011). [3] H. Imahori, H. Iijima, H. Hayashi, Y. Toude, T. Umeyama, Y. Matano, and S. Ito, ChemSusChem, 4, 797 (2011). [4] M. Simon, H. Iijima, Y. Toude, T. Umeyama, Y. Matano, S. Ito, N. V. Tkachenko, H. Lemmetyinen, and H. Imahori, J. Phys. Chem. C, 115, 14415 (2011). [5] H. Imahori, T. Umeyama, K. Kurotobi, and Y. Takano, Chem. Commun. (Feature Article), 48, 4032 (2012). [6] H. Hayashi, A. S. Touchy, Y. Kinjo, Y. Toude, K. Kurotobi, T. Umeyama, Y. Matano, and H. Imahori, ChemSusChem, 6, 508 (2013). [7] S. Ye, A. Kathiravan, H. Hayashi, Y. Tong, Y. Infahsaeng, P. Chabera, T. Pascher, A. P. Yartsev, S. Isoda, H. Imahori, and V. Sundström, J. Phys. Chem. C, 117, 6066 (2013). [8] K. Kurotobi, K. Kawamoto, Y. Toude, Y. Fujimori, Y. Kinjo, S. Ito, Y. Matano, and H. Imahori, Chem. Lett., 42, 725 (2013). [9] K. Kurotobi, Y. Toude, K. Kawamoto, Y. Fujimori, S. Ito, P. Chabera, V. Sundström, and H. Imahori, Chem. Eur. J., 19, 17075 (2013). [10] T. Higashino and H. Imahori, Dalton Trans. (Perspective), in press.

Modulation of photovoltaic behavior of dye-sensitized solar cells by electron donors of porphyrin dyes and cosensitization

Abstract Porphyrin dyes have received great attention due to their excellent photovoltaic performance in dye-sensitized solar cells (DSSCs). In this work, dyes XC1 – XC3 were synthesized by introducing various numbers of bis(4-methoxyphenyl)amino and p -hexyloxyphenyl groups to porphyrin meso -positions. The XC1 molecule contains two p -hexyloxyphenyl groups, and its DSSCs showed the power conversion efficiency of 4.81%. For XC2 and XC3 , the replacement of p -hexyloxyphenyl with diphenylamino groups can effectively enhance the light harvesting around 500 nm. However, the highest occupied molecular orbitals (HOMOs) were elevated too much, which suppressed the dye regeneration processes, leading to low cell efficiencies of 2.51% and 1.27% for XC2 , and XC3 , respectively. To further improve the cell performance, an anthracene derivative C1 was used as the cosensitizer for XC1 , which increased both the J sc and V oc values, with an improved efficiency of 5.75%.

Theoretical studies on the absorption spectra and intramolecular charge transfer of push-pull zinc porphyrin dyes for dye-sensitized solar cells

The electronic structures, absorption spectra and intramolecular charge transfer properties of five push-pull zinc porphyrin analogs with different donor group and π bridge have been investigated by density functional theory(DFT) and TD(time-dependent)-DFT approach. The results show that the asymmetrical substituted diphenylamine group is favorable to the Q-band absorption of porphyrin dyes. The absence of the acetylenic bond in the π bridge part leads to the result that the B-band and the Q-band are blue-shifted and their absorption strength become weaker compared with that containing acetylenic bond, respectively. The introduction of the benzothiadiazole into the π bridge improves the intramolecular charge transfer.