Design Of Dye-sensitized Solar Cells Research Articles

Simulation of Dye-sensitized Solar Cells Based on a Population Dynamics Model

Dye-sensitized solar cells are electrochemical devices with very interesting properties that provide an alternative to the conventional semiconductor solar cell technology. However, the details of the charge transport mechanisms, which include both electronic and ionic transport, are not yet fully understood. In this paper, we present a novel approach to dye-sensitized solar cell modeling and simulation which is based on population dynamics models that have recently been extensively used to model reactions between biological molecules. It is shown that the proposed model can be used to simulate the operation of dye-sensitized solar cells and produces I-V characteristics that are in qualitative agreement with the experimental ones. Furthermore, the model presented here can be used to optimize the characteristics and the design of dye-sensitized solar cells. Keywords: Dye-sensitized solar cells, modeling, simulation, population dynamics

Dye-sensitized solar cells on glass paper: TCO-free highly bendable dye-sensitized solar cells inspired by the traditional Korean door structure

Dye-sensitized solar cells (DSSCs) are considered a suitable photovoltaic system for urban applications and highly bendable DSSCs can be expanded to applications such as dispensable DSSCs for commercial advertising and small portable power sources. However, although many reports have shown flexible or highly bendable photoelectrodes using TCO-coated polymeric substrates or metal meshes, until now, few have shown highly bendable DSSCs using electrodes because the flexibility of a single electrode is not a critical issue for highly bendable DSSCs. Here, we report a new DSSC design, inspired by the traditional Korean door structure consisting of a paper-bonded wooden frame, and a process for TCO-free highly bendable DSSCs utilizing glass paper and metal mesh. In the new DSSC design, constituents such as stainless steel mesh and mesoporous TiO2 loaded with a Ru-complex dye were bonded on the glass paper, which was sputter-coated with Pt on one side and filled with electrolyte. The glass-paper-based flexible DSSCs showed 2% energy-conversion efficiency, which was maintained under bending until the radius of curvature reached 2 cm. The new glass-paper-based flexible DSSCs may have potential applications as low-cost highly bendable solar cells to overcome the limitations of conventional sandwich-type DSSCs.

Analysis and design of dye-sensitized solar cell

Abstract This paper presents a methodology to numerically investigate the influence of design and operating parameters on the performance of dye-sensitized solar cell (DSSC). A one-dimensional steady-state model of the DSSC coupled with a model to predict global irradiance on a terrestrial surface is utilized to analyze the performance of a DSSC installation. Hourly, daily, monthly and annual performance of a DSSC installation is systematically analyzed over a wide range of design and operating parameters and the optimum configuration is identified with the objective of maximizing the power density. Overall, this paper illustrates a methodology to ascertain the optimal design and operating configurations of a DSSC which can be extended to any terrain.

Pushing the Frontiers of First-Principles Based Computer Simulations of Chemical and Biological Systems

The Laboratory of Computational Chemistry and Biochemistry is active in the development and application of first-principles based simulations of complex chemical and biochemical phenomena. Here, we review some of our recent efforts in extending these methods to larger systems, longer time scales and increased accuracies. Their versatility is illustrated with a diverse range of applications, ranging from the determination of the gas phase structure of the cyclic decapeptide gramicidin S, to the study of G protein coupled receptors, the interaction of transition metal based anti-cancer agents with protein targets, the mechanism of action of DNA repair enzymes, the role of metal ions in neurodegenerative diseases and the computational design of dye-sensitized solar cells. Many of these projects are done in collaboration with experimental groups from the Institute of Chemical Sciences and Engineering (ISIC) at the EPFL.

Theoretical Procedure for Optimizing Dye-Sensitized Solar Cells: From Electronic Structure to Photovoltaic Efficiency

A step-by-step theoretical protocol based on density functional theory (DFT) and time-dependent DFT at both the molecular and periodic levels is proposed for the design of dye-sensitized solar cell (DSSC) devices including dyes and electrolyte additives. This computational tool is tested with a fused polycyclic pyridinium derivative as a novel dye prototype. First, the UV-vis spectrum of this dye alone is computed, and then the electronic structure of the system with the dye adsorbed on an oxide semiconductor surface is evaluated. The influence of the electrolyte part of the DSSC is investigated by explicitly taking into account the electrolyte molecules co-adsorbed with the dye on the surface. We find that tert-butylpyridine (TBP) reduces the electron injection by a factor of 2, while lithium ion increases this injection by a factor of 2.4. Our stepwise protocol is successfully validated by experimental measurements, which establish that TBP divides the electronic injection by 1.6 whereas Li(+) multiplies this injection by 1.8. This procedure should be useful for molecular engineering in the field of DSSCs, not only as a complement to experimental approaches but also for improving them in terms of time and resource consumption.

Built-in Quantum Dot Antennas in Dye-Sensitized Solar Cells

A new design of dye-sensitized solar cells involves colloidal semiconductor quantum dots that serve as antennas, funneling absorbed light to the charge separating dye molecules via nonradiative energy transfer. The colloidal quantum dot donors are incorporated into the solid titania electrode resulting in high energy transfer efficiency and significant improvement of the cell stability. This design practically separates the processes of light absorption and charge carrier injection, enabling us to optimize each of these separately. Incident photon-to-current efficiency measurements show a full coverage of the visible spectrum despite the use of a red absorbing dye, limited only by the efficiency of charge injection from the dye to the titania electrode. Time resolved luminescence measurements clearly relate this to Forster resonance energy transfer from the quantum dots to the dye. The presented design introduces new degrees of freedom in the utilization of quantum dot sensitizers for photovoltaic cells. In particular, it opens the way toward the utilization of new materials whose band offsets do not allow direct charge injection.

Large improvement of photon capture for a dye-sensitized solar cell integrated with a fluorescent layer

An integrated design of dye-sensitized solar cell with fluorescent layer is realized. A fluorescent layer is deposited on a fluorine-doped tin oxide (FTO) glass with a blank right above a N719 dye-sensitized TiO2 coating which is printed on the central area of the conductive face of the FTO glass. Current density–voltage characteristic measurement indicates that our integrated system largely enhances photon harvesting by 44% compared with a cell without a fluorescent layer, which is attributed to the improvement of photon harvesting from the spectrum range and the space area.

The Influence of Particle Sizes on the Optical Characteristics of Nanocrystalline TiO2 Films for Dye-Sensitized Solar Cells

AbstractIncreasing the light harvesting efficiency (LHE) of photovoltaic devices is important for improving the conversion efficiency of solar light into electricity. The optical properties of mesoporous TiO2 films for Dye-Sensitized Solar Cells (DSCs) were investigated by varying the size of the particles (20–150 nm). A four–flux optical model was used to describe the light absorption and scattering within the film. Reflectance and transmittance spectra were recorded by a spectrophotometer equipped with an integrating sphere. The wavelength-dependent absorption coefficient k(λ) and scattering coefficient s(λ) were determined for different films. The absorptance G(λ) (absorbed light flux) for films made of different particle sizes and of varying thicknesses can be calculated from these optical parameters. This study helps in improving the optical design of dye-sensitized solar cells.

Amphiphilic ruthenium dye as an ideal sensitizer in conversion of light to electricity using ionic liquid crystal electrolyte

The optimization of interfacial charge transfer between the dye and the electrolyte is crucial to the design of dye-sensitized solar cells. In this paper, we address the combined use of an ionic liquid crystal electrolyte and amphiphilic ruthenium dyes in dye-sensitized solar cells. The solar cell with an amphiphilic ruthenium dye [Ru(H 2dcbpy)(tdbpy)(NCS)2] (H 2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine, tdbpy = 4,4′-tridecyl-2,2′-bipyridine), exhibited a short-circuit photocurrent density of 9.1 mA/cm 2, an open-circuit voltage of 665 mV and a fill factor of 0.58, corresponding to an overall conversion efficiency of 3.51%. We find that increasing dye alkyl chain length to octadecyl from tridecyl results in lower short-circuit photocurrent density and open-circuit voltage, and the suitable dyes for ionic liquid crystal electrolyte differed completely from those used in liquid and ionic liquid electrolyte cells.

Portable, parallel grid dye-sensitized solar cell module prepared by screen printing

Screen-printing technology is used to fabricate large dye-sensitized solar cells (DSSCs). The high series-resistance associated with transparent conductive oxide glass substrates causes poor performance in large DSSCs especially at an exposure of 1 sun. The DSSC design has an embedded silver grid; a fluorine-doped tin oxide (FTO) glass substrate and stripe type titanium dioxide (TiO2) active layers introduced by screen-printing. The counter electrode is prepared from a screen printable paste based on hexachloro platinic acid. A DSSC module, which consists of five stripe-type working electrodes on a 5 cm × 5 cm, embedded silver grid FTO glass substrate, shows stable performance with an energy conversion efficiency of 5.45% under standard test conditions. © 2006 Elsevier B.V. All rights reserved.

The New Design of Dye-Sensitized Solar Cell Adopted by Sputter Deposition of Counter Electrode

The counter electrode widely used in DSCs (Dye-sensitized Solar Cells) is constructed of conducting glass substrates coated with Pt films, where the platinum acts as a catalyst. Pt counter electrodes in DSCs are one important component. It is expected that characteristics of Pt electrodes strongly depend on fabrication process and its surface condition. In this study, Pt counter electrode surface of DSC is deposited by RF sputtering under the conditions of Ar 6.7×10-1 Pa, RF power of 120 W and substrate temperature of 100°C. Surface morphology of Pt electrodes was investigated by FE-SEM and AFM. And this paper shows our recent results and technology to fabricate the new designed cell with Pt electrodes deposited by sputtering method. We have achieved fill factor 68% and photoelectric conversion efficiency around 2.6% as the best results of new designed DSCs structure.

Alkyl Chain Barriers for Kinetic Optimization in Dye-Sensitized Solar Cells

The optimization of interfacial charge transfer is crucial to the design of dye-sensitized solar cells. In this paper we address the dynamics of the charge separation and recombination in liquid-electrolyte and solid-state cells employing a series of amphiphilic ruthenium dyes with varying hydrocarbon chain lengths, acting as an insulating barrier for electron-hole recombination. Dynamics of electron injection, monitored by time-resolved emission spectroscopy, and of charge recombination and regeneration, monitored by transient optical absorption spectroscopy, are correlated with device performance. We find that increasing dye alkyl chain length results in slower charge recombination dynamics to both the dye cation and the redox electrolyte or solid-state hole conductor (spiro-OMeTAD). These slower recombination dynamics are however paralleled by reduced rates for both electron injection into the TiO2 electrode and dye regeneration by the I-/I3- redox couple or spiro-OMeTAD. Kinetic competition between electron recombination with dye cations and dye ground state regeneration by the iodide electrolyte is found to be a key factor for liquid electrolyte cells, with optimum device performance being obtained when the dye regeneration is just fast enough to compete with electron-hole recombination. These results are discussed in terms of the minimization of kinetic redundancy in solid-state and liquid-electrolyte dye-sensitized photovoltaic devices.

Theoretical modeling of TiO2/TCO interfacial effect on dye-sensitized solar cell performance

A theoretical model based on an integration of both Schottky barrier model and electron diffusion differential model was developed to determine the TiO2/TCO interfacial effect on the current–voltage (J–V) characteristics of a dye-sensitized solar cell (DSSC). The thermionic-emission theory was appropriately applied to describe the electron transfer at the TiO2/TCO interface. A parametric analysis was conducted to study how the photoelectric outputs varied with multiple independent variables, such as Schottky barrier height (φb) and temperature. It was found that the variation of the maximum DSSC power output (Pmax) was insignificant when φb varied at a low value; however, an increase in φb exceeding a critical value caused an apparent decrease in the maximum DSSC power output. The theoretical results were quantitatively compared and agreed very well with published theoretical results. The experimental data from literature were found to agree well with the present theoretical results, qualitatively validating the present model. The theoretical model can be applied to facilitate selection of suitable TCO material in DSSC design to avoid the adverse TiO2/TCO interfacial effect.

Internal Reference Electrode in Dye Sensitized Solar Cells for Three-Electrode Electrochemical Characterizations

A new design of dye-sensitized solar cells that contains an internal reference electrode enables detailed electrochemical characterization of the cells at the practical operating configuration. A thin insulating gap splits the nanoporous TiO2 electrode in twin halves, one serving as the active electrode in the solar cell and the other one as a photoreference that maintains the open circuit potential. This configuration allows separation of the two components of the cell potential, that of the photoactive electrode and that in the counter electrode, while maintaining the practical sandwich configuration. Analysis of efficient solar cells shows that the contributions of the counter electrode to the energy losses are larger than expected. By intentionally decreasing the counter electrode quality, we observed a modification of the photocurrent at the same effective electrode potential. This result is explained in terms of the coupling between the hole collection efficiency at the counter electrode and the rec...