Studies of coupled charge transport in dye-sensitized solar cells using a numerical simulation tool (original) (raw)
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Modeling of interfacial and bulk charge transfer in dye-sensitized solar cells
Cogent Engineering
A simple, first-principles mathematical model has been developed to analyze the effect of interfacial and bulk charge transfer on the power output characteristics of dye-sensitized solar cells (DSSCs). Under steady state operating conditions, the Butler-Volmer equation and Schottky barrier model were applied to evaluate the voltage loss at counter electrode/electrolyte and TiO 2 /TCO interfaces, respectively. Experimental data acquired from typical DSSCs tested in our laboratory have been used to validate the theoretical J-V characteristics predicted by the present model. Compared to the conventional diffusion model, the present model fitted the experimental J-V curve more accurately at high voltages (0.65-0.8 V). Parametric studies were conducted to analyze the effect of series resistance, shunt resistance, interfacial overpotential, as well as difference between the conduction band and formal redox potentials on DSSCs' performance. Simulated results show that a "lower-limit" of shunt resistance (10 3 Ωcm 2) is necessary to guarantee a maximized efficiency. The model predicts a linear relationship between open circuit voltage (V oc) and photoanode temperature (T) with a slope of −1 mV/°C, which is close to the experimental data reported in literature. Additionally, it is observed that a small value of overpotential (2.2 mV) occurs at the short-circuit condition (J sc = 10.5 mA/cm 2), which is in a close agreement with Volmer-Butler equation. This observation suggests that,
Physica Scripta, 2013
For a better understanding of the mechanisms of dye-sensitized solar cells (DSSCs), based on carbon nano-tube (CNT) electrodes, a phenomenological model is proposed. For modelling purposes, the meso-scopic porous CNT electrode is considered as a homogeneous nano-crystalline structure with thickness L. The CNT electrode is covered with light-absorbing dye molecules, and interpenetrated by the tri-iodide (I − /I − 3 ) redox couple. A simulation platform, designed to study coupled charge transport in such cells, is presented here. The work aims at formulating a mathematical model that describes charge transfer and charge transport within the porous CNT window electrode. The model is based on a pseudo-homogeneous active layer using drift-diffusion transport equations for free electron and ion transport. Based on solving the continuity equation for electrons, the model uses the numerical finite difference method. The numerical solution of the continuity equation produces current-voltage curves that fit the diode equation with an ideality factor of unity. The calculated current-voltage (J-V) characteristics of the illuminated idealized DSSCs (100 mW cm −2 , AM1.5), and the different series resistances of the transparent conductor oxide (TCO) layer were introduced into the idealized simulated photo J-V characteristics. The results obtained are presented and discussed in this paper. Thus, for a series resistance of 4 of the TCO layer, the conversion efficiency (η) was 7.49% for the CNT-based cell, compared with 6.11% for the TiO 2 -based cell. Two recombination kinetic models are used, the electron transport kinetics within the nano-structured CNT film, or the electron transfer rate across the CNT-electrolyte interface. The simulations indicate that both electron and ion transport properties should be considered when modelling CNT-based DSSCs and other similar systems. Unlike conventional polycrystalline solar cells which exhibit carrier recombination, which limits their efficiency, the CNT matrix (in CNT-based cells) serves as the conductor for majority carriers and prevents recombination. This is because of special conductivity and visible-near-infrared transparency of the CNT. Charge transfer mechanisms within the porous CNT matrix and at the semiconductor-dye-electrolyte interfaces are described in this paper.
Modeling, simulation and design of dye sensitized solar cells
RSC Adv., 2014
It is well known that recombination and transport rule the performance of dye sensitized solar cells (DSC's); although, the influence that these two phenomena have in their performance, particularly in the open circuit-potential (V oc) and in the short circuit current (J sc), is not fully understood. In this paper a phenomenological model is used to describe the quantitatively effect that transport and recombination have in the performance of the solar cell and their influence in its optimal design. The model is used to predict the influence of the recombination reaction rate constant (k r) and diffusion coefficient (D eff) in the V oc and in the J sc , whether a linear or non-linear recombination kinetic is considered. It is provided a methodology for decoupling the conduction band shifts from recombination effect in charge extraction experiments. Results also suggest that the influence of recombination in the V oc and in J sc is highly dependent on the reaction order considered. This fact highlights the importance of considering the reaction order when modeling data obtained by experimental methods. The combined results are analyzed and discussed in terms of the collection efficiency and in the optimization of the photoelectrode thickness. The model provides also a useful framework for exploring new concepts and designs for improving DSCs performance.
Phenomenological modeling of dye-sensitized solar cells under transient conditions
Solar Energy, 2011
A phenomenological model is proposed for a better understanding of the basic working mechanisms of dye-sensitized solar cells (DSCs). A steady-state approach allows the construction of the I–V characteristics, giving important informations about the main factors that influence DSCs’ performance. On the other hand, the transient approach model is an important tool to relate the phenomenological behavior with certain dynamic techniques, such as Electrochemical Impedance Spectroscopy (EIS). Bearing in mind the uncertainty arising from fitting the experimental Nyquist diagrams to general electrical analogues, this transient model contributes for a deeper understanding of the DSCs and for obtaining the relevant kinetic parameters with higher accuracy. The one-dimensional transient phenomenological model presented here assumes that the injected conduction-band electrons may recombine only with the electrolyte redox species. Due to the small dimension of the titania particles, no significant electrical potential gradient is considered, resulting only in a diffusive electron transport across the semiconductor. For modeling purposes, the mesoscopic porous structure, consisting of TiO2 nanoparticles covered with light-absorbing dye molecules and interpenetrated by the I-/I3- redox mediator (electrolyte), is considered as a homogeneous nanocrystalline structure of thickness L. The continuity and transport governing equations are defined for the mobile species involved: electrons in the TiO2 conduction band and I-/I3- ions in the electrolyte. The simulated results are in straight agreement with the experimental data.
Electron Transfer in Dye-Sensitized Solar Cells
The dye-sensitized solar cells (DSSC) have been regarded as one of the most promising new generation solar cells. Tremendous research efforts have been invested to improve the efficiency of solar energy conversion which is generally determined by the light harvesting efficiency, electron injection efficiency and undesirable electron lifetime. In this review, various characteristics of dye-sensitized nanostructured TiO 2 solar cells, such as working principle, electron transport and electron lifetime, were studied. The review avoids detailed mathematical and spectroscopic discussion, but rather tries to summarize the key conclusions relevant to materials design.
A comprehensive device modeling of solid-state dye-sensitized solar cell by MATLAB
INTERNATIONAL CONFERENCE ON MULTIFUNCTIONAL MATERIALS (ICMM-2019)
Dye-sensitized solar cell (DSSC) is technically and economically reliable alternative to the p-n junction photovoltaic devices. Recently, the energy conversion efficiency of DSSC has been reported to improve a lot using nanoporous electrode. Numerical modeling is effective strategies for depth understanding of the working mechanism of a solar cell. This paper illustrates the optimization of current density versus voltage (J-V) outcomes using MATLAB by varying the different physical parameter of DSSC like temperature (T), intensity(I), absorption coefficient (α) and thickness of electrode (d) in modeled simulation equation. Second order differential simulation equation has been used in present study for measurement of performance curve of Dye-sensitized solar cell. The current density versus voltage (J-V) curve for DSSC has also been calculated numerically using the internal variable such as diffusion coefficient (D), diffusion length (L), initial concentration of electrons (n 0) and thickness of electrode (t). The current density versus voltage (J-V) curve.