Photoinduced Charge Carrier Dynamics of Zn−Porphyrin−TiO<sub>2</sub> Electrodes: The Key Role of Charge Recombination for Solar Cell Performance

Imahori, Hiroshi; Kang, Soonchul; Hayashi, Hironobu; Haruta, Mitsutaka; Kurata, Hiroki; Isoda, Seiji; Canton, Sophie E.; Infahsaeng, Yingyot; Kathiravan, Arunkumar; Pascher, Torbjörn; Chábera, Pavel; Yartsev, Arkady; Sundström, Villy

doi:10.1021/jp103747t

Cited by 214 publications

(290 citation statements)

References 81 publications

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“…Therefore, despite their theoretical superiority, DSCs equipped with porphyrin sensitizers and Co(polypyridyl) redox couples largely fail to outperform those with ruthenium-based sensitizers and the I − /I 3 − system. Their inferior performance is primarily attributable to the severe molecular aggregation in porphyrin sensitizers induced by π-π stacking of the heterocyclic body on TiO 2 NP surfaces, charge recombination between the electron in the conduction band of the TiO 2 and porphyrin radical cation [ 10 ] as well as the sluggish mass transport of cobalt mediators in conventional mesoporous TiO 2 fi lms, [ 11 ] which lead to lower short-circuit currents ( J SC ) and consequently to low PCE.…”

Section: Introductionmentioning

confidence: 99%

Trifunctional TiO₂ Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

Zhai

Hsieh

Yeh

et al. 2015

Adv Funct Materials

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In this study, highly mesoporous TiO2 composite photoanodes composed of functional {001}‐faceted TiO2 nanoparticles (NPs) and commercially available 20 nm TiO2 NPs are employed in efficient porphyrin‐sensitized solar cells together with cobalt polypyridyl‐based mediators. Large TiO2 NPs (approximately 50 nm) with exposed {001} facets are prepared using a fast microwave‐assisted hydrothermal (FMAH) method. These unique composite photoanodes favorably mitigate the aggregation of porphyrin on the surface of TiO2 NPs and strongly facilitate the mass transport of cobalt‐polypyridyl‐based electrolytes in the mesoporous structure. Linear sweep voltammetry reveals that the transportation of Co(polypyridyl) redox is a diffusion‐controlled process, which is highly dependent on the porosity of TiO2 films. Electrochemical impedance spectroscopy confirms that the FMAH TiO2 NPs effectively suppress the interfacial charge recombination toward [Co(bpy)3]3+ because of their oxidative {001} facets. In an optimal condition of 40 wt% addition of FMAH TiO2 NPs in the final formula, the power conversion efficiency of the dye‐sensitized cells improves from 8.28% to 9.53% under AM1.5 (1 sun) conditions.

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Section: Introductionmentioning

confidence: 99%

Trifunctional TiO₂ Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

Zhai

Hsieh

Yeh

et al. 2015

Adv Funct Materials

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“…10,[18][19][20] Strategies to remove such limitations have driven the development of several new porphyrin dyes, [21][22][23][24] however, despite encouraging progress, the reasons for limitations in porphyrin sensitizer performance are not completely understood.…”

Section: Introductionmentioning

confidence: 99%

Cation Exchange at Semiconducting Oxide Surfaces: Origin of Light-Induced Performance Increases in Porphyrin Dye-Sensitized Solar Cells

et al. 2013

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The origin of simultaneous improvements in the short-circuit current density ( Jsc) and open-circuit voltage (Voc) of porphyrin dye-sensitized TiO2 solar cells following white light illumination was studied by systematic variation of several different device parameters. Reduction of the dye surface loading resulted in greater relative performance enhancements, suggesting open space at the TiO2 surface expedites the process. Variation of the electrolyte composition and subsequent analysis of the conduction band potential shifts suggested that a light-induced replacement of surface-adsorbed lithium (Li+) ions with dimethylpropylimidazolium (DMPIm+) ions was responsible for an increased electron lifetime by decreasing the recombination with the redox mediator. Variation of the solvent viscosity was found to affect the illumination time required to generate increased performance, while similar performance enhancements were not replicated by application of negative bias under dark conditions, indicating the light exposure effect was initiated by formation of dye cation molecules following photoexcitation. The substituents and linker group on the porphyrin chromophore were both varied, with light exposure producing increased electron lifetime and Voc for all dyes; however, increased Jsc values were only measured for dyes containing binding moieties with multiple carboxylic acids. It was proposed that the initial injection limitation and/or fast recombination process in these dyes arises from the presence of lithium at the surface, and the improved injection and/or retardation of fast recombination after light exposure is caused by the Li+ removal by cation exchange under illumination. there an initial injection limitation and/or fast recombination process in these dyes arises from the presence of lithium at the surface, and the improved injection and/or retardation of fast recombination after light exposure was caused by the Li + removal by cation exchange under illumination.

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“…The comparable values for τ 1 for all derivatives suggests that this EI process does not occur via the anchoring ligand, but instead directly from the zinc phthalocyanine core toward the TiO 2 , possibly via a through-space mechanism. 43 The second component can be attributed to a through-bond EI. Increasing the length of the spacer in between the anchoring ligand and the molecule (TT1 → TT6) slows down EI.…”

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confidence: 99%

Impact of the Anchoring Ligand on Electron Injection and Recombination Dynamics at the Interface of Novel Asymmetric Push–Pull Zinc Phthalocyanines and TiO₂

et al. 2013

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Phthalocyanines are promising photosensitizers for dye-sensitized solar cells (DSSCs). A parameter that has been problematic for a long time involves electron injection (EI) into the TiO 2 . The development of push−pull phthalocyanines shows great potential to improve the ratio of EI to back electron transfer (BET). We have studied the impact of the anchoring ligand on EI and BET using transient absorption. The best performing derivative, which has a dicarboxylic acid anchoring ligand (TT15, DSSC efficiency of 3.96%), shows the fastest EI. The EI process occurs via an ultrafast component (∼700 fs for all derivatives) and a slower component (5.8 ps for TT15). The ps component is considerably slower for the other derivatives studied. Also BET depends on the anchoring ligand and is the slowest for TT15. This knowledge is essential for the optimization of the EI/BET ratio and the efficiency of a phthalocyanine-based DSSC. ■ INTRODUCTIONThe dye-sensitized solar cell (DSSC) is a low-cost alternative to conventional solid-state photovoltaic devices.1 The heart of a DSSC involves the interface between a semiconductor nanoparticle (usually TiO 2 ) and a photosensitizer molecule. Excitation of the photosensitizer should lead to efficient electron injection (EI) into the semiconductor; recombination or back electron transfer (BET) has to be avoided to allow electrons to diffuse away from the interface. Among the most successful photosensitizers are polypyridylruthenium complexes, with efficiencies up to 10−11%. 2,3 In the region with strong absorption, incident photons are converted into charges with close to unity efficiency, indicating a high EI/BET ratio. Utilization of the red part of the visible spectrum where the solar flux is maximum is however problematic due to lack of absorption in this region.Phthalocyanines are well-known for their intense absorption in the red/near-IR region of the solar spectrum and excellent photochemical stability. DSSC devices based on phthalocyanines, however, have shown efficiencies below 1% for a long time.4,5 This is likely caused by a low EI/BET ratio. Recently, significantly higher efficiencies up to about 6% have been realized. 6−14 An important tool in the development toward higher efficiencies involves the prevention of aggregation and the introduction of directionality in the electron transfer process. Only the chemical functionality anchored onto the TiO 2 should attract the electron, while functionalities not attached to the TiO 2 should be both electron-pushing and bulky enough to prevent aggregation.An important aspect to address is the ideal chemical structure of the anchoring group. It should attach the phthalocyanine molecule onto the semiconductor. Carboxylic acid functionalities are known to bind to metal oxide surfaces and therefore often applied as anchoring side group. 15,16 According to the Marcus theory, 17 the electronic coupling between electron donor and acceptor is an important parameter determining the electron transfer rate. The mutual orientation of...

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Photoinduced Charge Carrier Dynamics of Zn−Porphyrin−TiO₂ Electrodes: The Key Role of Charge Recombination for Solar Cell Performance

Cited by 214 publications

References 81 publications

Trifunctional TiO₂ Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

Trifunctional TiO₂ Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

Cation Exchange at Semiconducting Oxide Surfaces: Origin of Light-Induced Performance Increases in Porphyrin Dye-Sensitized Solar Cells

Impact of the Anchoring Ligand on Electron Injection and Recombination Dynamics at the Interface of Novel Asymmetric Push–Pull Zinc Phthalocyanines and TiO₂

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Photoinduced Charge Carrier Dynamics of Zn−Porphyrin−TiO2 Electrodes: The Key Role of Charge Recombination for Solar Cell Performance

Cited by 214 publications

References 81 publications

Trifunctional TiO2 Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

Trifunctional TiO2 Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

Cation Exchange at Semiconducting Oxide Surfaces: Origin of Light-Induced Performance Increases in Porphyrin Dye-Sensitized Solar Cells

Impact of the Anchoring Ligand on Electron Injection and Recombination Dynamics at the Interface of Novel Asymmetric Push–Pull Zinc Phthalocyanines and TiO2

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Photoinduced Charge Carrier Dynamics of Zn−Porphyrin−TiO₂ Electrodes: The Key Role of Charge Recombination for Solar Cell Performance

Trifunctional TiO₂ Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

Trifunctional TiO₂ Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

Impact of the Anchoring Ligand on Electron Injection and Recombination Dynamics at the Interface of Novel Asymmetric Push–Pull Zinc Phthalocyanines and TiO₂