Dye-sensitized Nanocrystalline Solar Cells Research Articles

A new improved structure of dye-sensitized solar cells with reflection film

A new improved structure of dye-sensitized nanocrystalline solar cells (DSSC) for utilizing reflected light was introduced in this paper. Typical DSSC is based on a sandwich structure, which consists of photoanode, electrolyte and cathode. For the improved structure of DSSC in this paper, a sliver reflection film was attached to the back of transparent conducting glass of cathode. In this way, the residual light passing through photoanode was reflected to it to be used again. The photocurrent-voltage characteristics of DSSC fabricated by two different thickness of TiO2 film were measured to illustrate the effects of utilizing reflected light. As a result, the improved DSSC with reflection film exhibited higher photocurrent and solar-to-electric conversion efficiency than DSSC without reflection film.

Computer simulations of light scattering and mass transport of dye-sensitized nanocrystalline solar cells

Abstract Light scattering of nanocrystalline TiO2 porous film with a double layer structure is studied by computer simulations in terms of four-flux radiative transfer model. Efficient light scattering in the double layer film composed of a transparent layer containing 10 nm particles and a scattering layer containing a mixture of 10 and 150 nm particles is obtained by optimizing the film structure. An increase of the light absorption from the strong light scattering of the double layer film and the contribution of back reflection at the counter electrode leads to improve the total photocurrent density significantly. Limitation of the maximum total photocurrent density of the double layer film by the mass transport of the redox species is examined in virtue of the dependence of the diffusion limiting current densities on film structure under different diffusion coefficients of the redox species I - / I 3 - .

Modification of photocathode of dye-sensitized nanocrystalline solar cell with platinum by vacuum coating, thermal decomposition and electroplating

Conducting glass substrates are modified with platinum by vacuum coating, thermal decomposition and electrochemical sedimentation methods. A dye-sensitized nanocrystalline solar cell (DSC) is assembled by using a substrate modified with platinum as photocathode. The surface status of the photoanode is observed, the surface resistance of the substrate is measured, and the influence of the photoanode on the photoelectrical efficiency of the DSC is investigated. It is found that the platinum film prepared by the electrochemical sedimentation method with a plane, shining and uniform appearance shows lower surface resistance and better photoelectric efficiency than that prepared by the other two methods. The surface resistance is 12.4 Ω · cm−1, using it as photoanode, and the DSC's open circuit voltage, short current and fill factor is 6.2 mA/cm2, 0.662 V and 52.3%, respectively.

Interface engineering for solid-state dye-sensitised nanocrystalline solar cells: the use of an organic redox cascade

We demonstrate the formation of a charge transfer cascade at a nanostructured TiO2/dye/polymer/molecular hole transport multilayer interface. Charge recombination dynamics at this interface are shown to be retarded when the ionisation potential of the polymer layer exceeds that of the molecular hole transport layer.

Characterization and Modeling of Transport and Interfacial Transfer of Electrons in Dye-Sensitized Solar Cells

ABSTRACTFactors that determine the performance of dye-sensitized nanocrystalline solar cells are discussed

Dye-sensitized nanocrystalline solar cells incorporating ethylmethylimidazolium-based ionic liquid electrolytes

Abstract High-performance dye-sensitized solar cells incorporating electrochemically stable non-volatile electrolytes are especially desirable devices. In particular, ionic liquid systems based on ethylmethylimidazolium dicyanamide seem to be promising for this purpose. These have triggered our interest in the properties of further ethylmethylimidazolium-based ionic liquids with anions which are close relatives of dicyanamide. In this study, the effect of three different anions, tricyanomethanide, dicyanamide and thiocyanate, on the performance of dye-sensitized solar cells have been investigated. Both the short circuit photocurrent and conversion efficiency are increased with decreasing viscosity of the ionic liquids under comparable conditions. A conversion efficiency of 2.1% at 30% light intensity was observed for the cell containing the tricyanomethanide salt, which has lowest viscosity among the three ionic liquids, while efficiencies of 0.7% and 1.7% at the same light intensity were observed in the case of dicyanamide and thiocyanate salts, respectively, as an electrolyte. To cite this article: Q. Dai et al., C. R. Chimie 9 (2006).

A novel hybrid nanocrystalline TiO2 electrode for the dye-sensitized nanocrystalline solar cells

A novel hybrid nanocrystalline TiO2 electrode for the dye-sensitized nanocrystalline solar cells

Determination of the Density and Energetic Distribution of Electron Traps in Dye-Sensitized Nanocrystalline Solar Cells

Electron transport and recombination in dye-sensitized nanocrystalline solar cells (DSCs) are strongly influenced by the presence of trapping states in the titanium dioxide particles, and collection of photoinjected electrons at the contact can require times ranging from milliseconds to seconds, depending on the illumination intensity. A direct method of determining the density and energetic distribution of the trapping states responsible for slowing electron transport has been developed. It involves extraction of trapped electrons by switching the cell from an open circuit to a short circuit after a period of illumination. An advantage of this charge extraction method is that it is less sensitive than other methods to shunting of the DSC by electron transfer at the conducting glass substrate. Results derived from charge extraction measurements on DSCs (with and without compact TiO(2) blocking layers) are compared with those obtained by analysis of the open circuit photovoltage decay.

ELECTRON INJECTION AT DYE-SENSITIZED SEMICONDUCTOR ELECTRODES

Electron injection at dye-sensitized semiconductors is reviewed. Particular emphasis is placed on theoretical and photoelectrochemical studies of dye-sensitized planar and single-crystal electrodes. The accepted mechanism of electron injection, which was derived from these classical studies, is introduced. Selected photoelectrochemical studies of dye-sensitized nanocrystalline semiconductors are reviewed; emphasis is given to factors that influence the efficiencies of electron injection and charge recombination. The development of quasi-solid-state nanocrystalline dye-sensitized solar cells is also discussed. Recent time-resolved spectroscopic studies of electron injection and charge recombination are reviewed. These studies have led to a better understanding of electron injection mechanisms, and have revealed the limitations of the classical models.

How Does Back-Reaction at the Conducting Glass Substrate Influence the Dynamic Photovoltage Response of Nanocrystalline Dye-Sensitized Solar Cells?

In dye-sensitized nanocrystalline solar cells (DSC), the transfer of electrons from the conducting glass substrate to triiodide ions in solution is an important loss mechanism that can be suppressed by using thin compact blocking layers of TiO(2). Whereas back-reaction at the substrate is relatively unimportant under short circuit conditions, it must be taken into account at the maximum power point or at open circuit. The influence of the back-reaction on open circuit photovoltage decay measurements and on intensity modulated photovoltage (IMVS) measurements has been studied by model simulations and by experimental measurements. The simulations demonstrate that reliable information about DSC properties such as trapping distributions can only be derived from transient or periodic photovoltage responses if the back-reaction is suppressed by the use of suitable blocking layers.

Stable ⩾8% efficient nanocrystalline dye-sensitized solar cell based on an electrolyte of low volatility

We demonstrate a ⩾8% efficient nanocrystalline dye-sensitized solar cell retaining over 98% of its initial performance after 1000 h of accelerated tests subjected to thermal stress at 80 °C in the dark. Device degradation was also negligible following 1000 h of visible light soaking at 60 °C. This high performance and stable device was realized by using a robust electrolyte of low volatility in conjunction with the amphiphilic ruthenium sensitizer [Ru(4,4′-dicarboxylic acid-2,2′-bipyridine)(4,4′-bis(p-hexyloxystyryl)-2,2′-bipyridine)(NCS)2], coded as K-19, which was grafted together with 1-decylphosphonic acid on the mesoporous titania film acting as photoanode.

Grain Morphology and Trapping Effects on Electron Transport in Dye-Sensitized Nanocrystalline Solar Cells

We have examined the combined effects of grain morphology and electron trapping on the transient response of photoelectrons moving through the TiO2 grains in a dye-sensitized nanocrystalline solar cell using a multi-time-scale random walk Monte Carlo model. Our use of a multi-time-scale approach enables us to simulate transport for electrons moving through spherical connected grains in a three-dimensional (3D) voided network and look at the effect of the size of interparticle boundaries on carrier dynamics. We can also address similar times to those over which measurements are taken, namely, 0.1 ms. These times are long because of deep traps in the TiO2 grains. The grains have 2-fold connectivity in one dimension (linear chains) or 4-fold or 6-fold connectivity in three dimensions and traps with an exponential distribution of energies. Photoelectrons are generated by a light pulse of short duration. The spatial distribution of the photogenerated electron density from this pulse either has a uniform profile or is peaked on the electrolyte side. We show that the constrictions at the grain necks slow the electrons, making trapping more likely and hence further delaying their passage to the extracting electrode. By comparing our results for 4-fold and 6-fold coordinated particles on a cubic lattice with 2-fold coordinated particles on linear chains, we show that transport is slowed in the former case due to the additional paths available to the electrons in the 3D network. We also find that the charge and current transients cannot be fit to an analytical solution of the continuum equations with an effective diffusion coefficient even at long times. Therefore, caution must be exercised when attempting to fit experimental transient data with an effective diffusion coefficient.

Charge Separation versus Recombination in Dye-Sensitized Nanocrystalline Solar Cells: the Minimization of Kinetic Redundancy

In this paper we focus upon the electron injection dynamics in complete dye-sensitized nanocrystalline metal oxide solar cells (DSSCs). Electron injection dynamics are studied by transient absorption and emission studies of DSSCs and correlated with device photovoltaic performance and charge recombination dynamics. We find that the electron injection dynamics are dependent upon the composition of the redox electrolyte employed in the device. In a device with an electrolyte composition yielding optimum photovoltaic device efficiency, electron injection kinetics exhibit a half time of 150 ps. This half time is 20 times slower than that for control dye-sensitized films covered in inert organic liquids. This retardation is shown to result from the influence of the electrolyte upon the conduction band energetics of the TiO2 electrode. We conclude that optimum DSSC device performance is obtained when the charge separation kinetics are just fast enough to compete successfully with the dye excited-state decay. These conditions allow a high injection yield while minimizing interfacial charge recombination losses, thereby minimizing "kinetic redundancy" in the device. We show furthermore that the nonexponential nature of the injection dynamics can be simulated by a simple inhomogeneous disorder model and discuss the relevance of our findings to the optimization of both dye-sensitized and polymer based photovoltaic devices.

Multi-timescale Monte Carlo method for simulating electron transport in dye-sensitized nanocrystalline solar cells

We present a novel multi-timescale approach to simulating transport for electrons moving through a mesoporous film of TiO2 grains in the dye-sensitized solar cell. This method is unique in its ability to integrate microscopic (intra-grain) with mesoscopic (inter-grain) charge transport processes. Comparisons are made with experimental measurements of transient currents.

A novel method for preparing platinized counter electrode of nanocrystalline dye-sensitized solar cells

The platinized FTO glass counter electrode was prepared by employing techniques of colloid preparation, Langmuir-Blodgett film and self-assembly. The present electrode had very low platinum loading, high catalytic activity for iodine/triiodide reduction reaction. Compared with the conventional counter electrodes used in nanocrystalline dye-sensitized solar cells, the present electrode had provided a much higher catalytic performance which was attributed to the structure of platinum nanoclusters distributed homogeneously on the electrode.

A High Molar Extinction Coefficient Sensitizer for Stable Dye-Sensitized Solar Cells

An amphiphilic heteroleptic polypyridyl ruthenium complex with a high molar extinction coefficient was synthesized and demonstrated as an efficient, thermostable sensitizer in nanocrystalline dye-sensitized solar cells.

How Important is the Back Reaction of Electrons via the Substrate in Dye-Sensitized Nanocrystalline Solar Cells?

The role of the conducting glass substrate (fluorine-doped tin oxide, FTO) in the back reaction of electrons with tri-iodide ions in dye-sensitized nanocrystalline solar cells (DSCs) has been investigated using thin-layer electrochemical cells that are analogues of the DSCs. The rate of back reaction is dependent on the type of FTO and the thermal treatment. The results show that this back-reaction route cannot be neglected in DSCs, particularly at lower light intensities, where it is the dominant route for the back transfer of electrons to tri-iodide. This conclusion is confirmed by measurements of the intensity dependence of the photovoltages of DSCs with and without blocking layers. It follows that blocking layers should be used to prevent the back reaction in mechanistic studies in which the light intensity is varied over a wide range. Conclusions based on studies of the intensity dependence of the parameters of DSCs such as photovoltage and electron lifetime in cells without blocking layers, must be critically re-examined.

Enhancement in Photoelectric Conversion Properties of the Dye-Sensitized Nanocrystalline Solar Cells Based on the Hybrid TiO2 Electrode

A hybrid electrode containing a sputter-deposited layer and a nanocrystalline layer was fabricated on a conducting glass by dc magnetron sputtering and the doctor blade technique, respectively. The sputter-deposited layer (20-40 nm) fabricated at 100-250°C is found to be outstanding for improving the performance of the dye-sensitized solar cells. In this case, a high solar-to-electric energy conversion efficiency of 8.1%, larger short-circuit photocurrent of and open-circuit voltage of 682 mV were attained under irradiation of white light Compared with the pure nanocrystalline electrodes, this hybrid has an improvement of one time in short-circuit current density and nearly one-third in open-circuit voltage. These suggest that this hybrid electrode has a potential for improving the performance of the dye-sensitized nanocrystalline solar cells. © 2004 The Electrochemical Society. All rights reserved.

Flexible, Dye-Sensitized Nanocrystalline Solar Cells Employing Biocatalytically Synthesized Polymeric Electrolytes

A variety of tethered PEGylated polymers were synthesized using a mild, environmentally benign, and highly selective biocatalytic approach for preparing a quasi-solid electrolyte system for dye-sensitized nanocrystalline solar cells (DSSC). The biocatalytic approach developed is based on immobilized Candida antarctica lipase B (Novozyme-435)-catalyzed copolymerization reactions; the polymeric materials thus-obtained were further functionalized with hydrophobic and hydrophilic side chains using mild chemical reactions. All these polymeric materials were used in formulating quasi-solid electrolyte compositions and incorporated into flexible DSSCs, and solar conversion efficiency of as high as 4.6% was obtained.

Stable New Sensitizer with Improved Light Harvesting for Nanocrystalline Dye‐Sensitized Solar Cells

A new heteroleptic polypyridyl ruthenium complex (see Figure) with a high molar extinction coefficient has been synthesized. The complex is demonstrated to be a highly efficient, stable sensitizer for nanocrystalline dye-sensitized solar cells. For a newly developed dye, the achievement of 10.2 % power conversion efficiency is very encouraging.