Dye adsorption, desorption, and distribution in mesoporous TiO2 films, and its effects on recombination losses in dye sensitized solar cells

O’Regan, Brian C.; Li, Xiaoe; Ghaddar, Tarek H.

doi:10.1039/c2ee21341a

Cited by 117 publications

(134 citation statements)

References 73 publications

(95 reference statements)

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“…5 Figure 1c compares the half-life of the fully dyed D131 sensitized sample with samples where the D131 loading was decreased either by using a short dyeing time or by using the coadsorbent DCA to limit the uptake of the dye to the surface. 25 The case of partial dye desorption is also presented in Section 2 of the Supporting Information. shows that hole lifetimes are consistently shorter for the sample with full coverage than for samples with decreased dye loading, even for concentrations of photo-generated electrons much lower than the total electron density (nph < n/10, see experimental section).…”

Section: Resultsmentioning

confidence: 99%

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films

et al. 2016

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Charge recombination between oxidized dyes attached to mesoporous TiO2 and electrons in the TiO2 was studied in inert electrolytes using transient absorption spectroscopy. Simultaneously, hole transport within the dye monolayers was monitored by transient absorption anisotropy. The rate of recombination decreased when hole transport was inhibited selectively, either by decreasing the dye surface coverage or by changing the electrolyte environment. From Monte Carlo simulations of electron and hole diffusion in a particle, modelled as a cubic structure, we identify the conditions under which hole lifetime depends on the hole diffusion coefficient for the case of normal (disorder free) diffusion. From simulations of transient absorption and transient absorption anisotropy, we find that the rate and the dispersive character of hole transport in the dye monolayer observed spectroscopically can be explained by incomplete coverage and disorder in the monolayer. We show that dispersive transport in the dye monolayer combined with inhomogeneity in the TiO2 surface reactivity can contribute to the observed stretched electron-hole recombination dynamics and electron density dependence of hole lifetimes. Our experimental and computational analysis of lateral processes at interfaces can be applied to investigate and optimize charge transport and recombination in solar energy conversion devices using electrodes functionalized with molecular light absorbers and catalysts.

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Section: Resultsmentioning

confidence: 99%

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films

et al. 2016

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“…30 The TRACER system provides bias light from 10 one Watt white LEDs with focusing optics (Lumileds). Pulse illumination is provided with 5 one Watt red LEDs.…”

Section: Experimental Methodsmentioning

confidence: 99%

Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO₂: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J–V Hysteresis

et al. 2015

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We have examined methylammonium lead iodide (MAPI) cells of the design FTO/sTiO 2 / mpTiO 2 /MAPI/Spiro-OMeTAD/Au using fast opto-electronic techniques including transient photovoltage, differential capacitance, charge extraction, current interrupt, and chronophotoamperometry. The data allow several important conclusions regarding the physics and proper characterization of these cells. 1) In mpTiO 2 /MAPI cells there are two kinds of extractable charge stored under operation: a capacitive electronic charge (~0.2 µC/cm 2 ), and another, much larger, charge (40 µC/cm 2 ) which could be the result of dipole realignment, or the effect of mobile ions. The capacitive charge is ~10 times smaller than in mpTiO 2 /dye/SpiroOMeTAD cells with similar mpTiO 2 thickness. 2) Transient photovoltage decays are strongly double exponential with two time constants that differ by a factor of ~5, independent of bias light intensity. We show that the fast decay (~1 µs at one sun) can be assigned to the predominant charge recombination pathway in the cell. We examine and reject the possibilities that the fast decay is due to ferro-electric relaxation, or to the bulk photovoltaic effect. We provide two possible schematic electrical models for the cells that reproduce the V oc and TPV data.3) It has been previously observed that MAPI cells frequently show current/voltage hysteresis. For example, an increase in J sc and V oc is observed on the return sweep of a cyclic JV. Our capacitance vs V oc data indicate that the hysteresis involves a change in internal potential gradients, most likely a shift in band offsets at the TiO 2 /MAPI interface. The TPV results show that the V oc hysteresis is not due to a change in recombination rate constant. Calculation of recombination flux at V oc shows that the hysteresis is also not due to an increase in charge separation efficiency, and that charge generation is not a function of applied bias. We also show that the JV hysteresis is not a light driven effect, but is caused by exposure to forward bias, light or dark.

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“…For the case of films dyed with D131 only, sufficiently long dyeing time is needed to guarantee full coverage throughout the depth of the film, as also discussed in reference 27 . When the inert coadsorbent chenodeoxycholic acid (DCA) was included in the dye solution to obtain lower dye loading, we observe slow uptake kinetics of D131 on the surface due to the presence of the DCA.…”

Section: Study Of Hole Percolation At Different Scalesmentioning

confidence: 99%

The Role of Hole Transport between Dyes in Solid-State Dye-Sensitized Solar Cells

Moia¹,

Cappel²,

Leijtens

et al. 2015

J. Phys. Chem. C

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In dye-sensitized solar cells (DSSCs) photo-generated positive charges are normally considered to be carried away from the dyes by a separate phase of hole transporting material (HTM). We show that there can also be significant transport within the dye monolayer itself before the hole reaches the HTM. We quantify the fraction of dye regeneration in solid state DSSCs that can be attributed to this process. By using cyclic voltammetry and transient anisotropy spectroscopy we demonstrate that the rate of inter-dye hole transport is prevented both on micrometer and nanometer length scales by reducing the dye loading on the TiO2 surface. The dye regeneration yield is quantified for films with high and low dye loadings (with and without hole percolation in the dye monolayer) infiltrated with varying levels of HTM. Inter-dye hole transport can account for >50% of the overall dye regeneration with low HTM pore filling. This is reduced to about 5% when the infiltration of the HTM in the pores is optimized in 2μm thick films. Finally, we use hole transport in the dye monolayer to characterize the spatial distribution of the HTM phase in the pores of the dyed mesoporous TiO2.

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Dye adsorption, desorption, and distribution in mesoporous TiO2 films, and its effects on recombination losses in dye sensitized solar cells

Cited by 117 publications

References 73 publications

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films

Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO₂: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J–V Hysteresis

The Role of Hole Transport between Dyes in Solid-State Dye-Sensitized Solar Cells

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Dye adsorption, desorption, and distribution in mesoporous TiO2 films, and its effects on recombination losses in dye sensitized solar cells

Cited by 117 publications

References 73 publications

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films

Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO2: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J–V Hysteresis

The Role of Hole Transport between Dyes in Solid-State Dye-Sensitized Solar Cells

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Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO₂: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J–V Hysteresis