Electronic Transport in Dye-Sensitized Nanoporous TiO<sub>2</sub> Solar CellsComparison of Electrolyte and Solid-State Devices

Kron, Gerald E.; Egerter, T.; Werner, A.; Rau, Uwe

doi:10.1021/jp0222144

Cited by 126 publications

(124 citation statements)

References 36 publications

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“…This denomination, adopted recently in some papers in the DSSC area 50,51 (and also used by us sometimes), is not very fortunate because diffusion is an irreversible energy loss process, whereas the capacitance is a reversible energy storage element. It is well-known that diffusion is caused by a local difference of chemical potentials.…”

Section: Relationship Of Chemical Capacitance To Diffusionmentioning

confidence: 99%

Interpretation of the Time Constants Measured by Kinetic Techniques in Nanostructured Semiconductor Electrodes and Dye-Sensitized Solar Cells

2004

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The processes of charge separation, transport, and recombination in dye-sensitized nanocrystalline TiO 2 solar cells are characterized by certain time constants. These are measured by small perturbation kinetic techniques, such as intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS), and electrochemical impedance spectroscopy (EIS). The electron diffusion coefficient, D n , and electron lifetime, τ n , obtained by these techniques are usually found to depend on steady-state Fermi level or, alternatively, on the carrier concentration. We investigate the physical origin of such dependence, using a general approach that consists on reducing the general multiple trapping kinetic-transport formalism, to a simpler diffusion formalism, which is valid in quasi-static conditions. We describe in detail a simple kinetic model for diffusion, trapping, and interfacial charge transfer of electrons, and we demonstrate the compensation of trap-dependent factors when forming steady-state quantities such as the diffusion length, L n , or the electron conductivity, σ n .

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Section: Relationship Of Chemical Capacitance To Diffusionmentioning

confidence: 99%

Interpretation of the Time Constants Measured by Kinetic Techniques in Nanostructured Semiconductor Electrodes and Dye-Sensitized Solar Cells

2004

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“…Presently, DSSC can achieve as much as 10% energy conversion efficiency (Gratzel, 2001). The ongoing research and development focus on new DSSC materials for higher cell efficiency and theoretical modelling for insightful understanding of the basic working mechanisms (Ruile et al, 1997;Gratzel, 2000;Kron et al, 2002Kron et al, , 2003aKron et al, , 2003bRau et al, 2003;Durr et al, 2004;Fredin et al, 2005;Lenzmann et al, 2005;Gratzel, 2006;Ito et al, 2006;Kroon et al, 2006;Kumara et al, 2006;Ni et al, 2006a;Pettersson et al, 2006;Sastrawan et al, 2006). Some studies have been conducted to determine the effect of the TiO 2 electrode thickness on the DSSC performance.…”

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confidence: 99%

Theoretical modelling of the electrode thickness effect on maximum power point of dye‐sensitized solar cell

Leung

2008

Can J Chem Eng

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The maximum power point (MPP) of a dye‐sensitized solar cell (DSSC) is often more important than the open‐circuit voltage and the short‐circuit current as MPP better represents the DSSC power output and energy conversion efficiency. In this investigation, the DSSC J–V characteristics and MPP were studied using a simple theoretical electron diffusion model. Parametric analyses were performed to determine the particular effect of electrode thickness on the MPP output. The analytical results are well consistent with the experimental results published in the literature. In the optimization analysis, it was specially found that the optimal electrode thickness for the highest MPP is rather insensitive to the operating conditions. It implies that an optimally designed DSSC can be always operated at its highest MPP regardless of any geographical, seasonal, and solar hour factors. Such an important attribute facilitates the design and manufacture of DSSC for worldwide commercialization at competitive costs.

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“…[8][9][10][11] However, very few studies address the nature of the contacts between the semiconductors and the electrodes. [12][13][14][15] We show that the size of a Schottky barrier, present at the anode interface, is dramatically reduced under UV illumination. We attribute this to the generation of surface states, resulting in a "pinning" of the Fermi level (E F ) in the semiconductor at this junction.…”

mentioning

confidence: 78%

The Role of a “Schottky Barrier” at an Electron‐Collection Electrode in Solid‐State Dye‐Sensitized Solar Cells

2006

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The field of polymer, molecular, and hybrid optoelectronics is progressing at a phenomenal pace with new records for material properties and nanostructured composites being reported regularly. [1][2][3][4][5] The promise of cheap, large-area, flexible solar cells, displays, and printable electronics is close to becoming a reality. However, connecting the functional components to the "outside world" can limit the end performance of the systems. The characteristics of the functional materials are often completely governed by the nature of the interfaces between the electrodes and these materials. [6,7] Here, we show that a "Schottky barrier" present at an electron-collecting electrode governs the performance of a solid-state dye-sensitized solar cell. This is a hybrid system comprising of light-absorbing sensitizer molecules at the interface between a nanostructured inorganic (n-type) and an organic (p-type) semiconductor. There has been much work concentrating on the dynamics, kinetics, and physical processes occurring at the dye interface. [8][9][10][11] However, very few studies address the nature of the contacts between the semiconductors and the electrodes. [12][13][14][15] We show that the size of a Schottky barrier, present at the anode interface, is dramatically reduced under UV illumination. We attribute this to the generation of surface states, resulting in a "pinning" of the Fermi level (E F ) in the semiconductor at this junction. We tune the size of the barrier by controlling the "doping level" in the inorganic semiconductor; reduction of the barrier height results in significant improvements in device performance. The solid-state dye-sensitized solar cell comprises of a fluorine-doped tin-oxide (FTO) semitransparent anode, a nanoporous TiO 2 film coated with a monolayer of dye molecules, infiltrated with the organic hole transporter 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-MeOTAD) and caped with a gold cathode.[16] A compact TiO 2 layer is inserted between the FTO and the nanoporous TiO 2 in order to reduce losses through recombination between holes in the hole transporter and electrons in the FTO. A compact TiO 2 layer is also occasionally employed in the "liquid cell" where a liquid electrolyte is used in place of Spiro-MeOTAD. [17,18] A phenomenon associated with dye-sensitized solar cells is the "UV effect", where the solar-cell performance is observed to improve dramatically when exposed to UV light. [19,20] The observed behavior has been explained by the generation of surface states on the TiO 2 nanoparticles. There is uncertainty as to the exact nature of these surface states, whether they are neutral or charged.[21] However, a consistency throughout is that an apparent positive shift in the conduction band is always observed under UV illumination (in this work positive is with respect to the normal hydrogen electrode (NHE), which is more negative with respect to the vacuum energy). This has the effect of improving electron injection from the lowest unoccupied...

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Electronic Transport in Dye-Sensitized Nanoporous TiO₂ Solar CellsComparison of Electrolyte and Solid-State Devices

Cited by 126 publications

References 36 publications

Interpretation of the Time Constants Measured by Kinetic Techniques in Nanostructured Semiconductor Electrodes and Dye-Sensitized Solar Cells

Interpretation of the Time Constants Measured by Kinetic Techniques in Nanostructured Semiconductor Electrodes and Dye-Sensitized Solar Cells

Theoretical modelling of the electrode thickness effect on maximum power point of dye‐sensitized solar cell

The Role of a “Schottky Barrier” at an Electron‐Collection Electrode in Solid‐State Dye‐Sensitized Solar Cells

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Electronic Transport in Dye-Sensitized Nanoporous TiO2 Solar CellsComparison of Electrolyte and Solid-State Devices

Cited by 126 publications

References 36 publications

Interpretation of the Time Constants Measured by Kinetic Techniques in Nanostructured Semiconductor Electrodes and Dye-Sensitized Solar Cells

Interpretation of the Time Constants Measured by Kinetic Techniques in Nanostructured Semiconductor Electrodes and Dye-Sensitized Solar Cells

Theoretical modelling of the electrode thickness effect on maximum power point of dye‐sensitized solar cell

The Role of a “Schottky Barrier” at an Electron‐Collection Electrode in Solid‐State Dye‐Sensitized Solar Cells

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Electronic Transport in Dye-Sensitized Nanoporous TiO₂ Solar CellsComparison of Electrolyte and Solid-State Devices