Initial Light Soaking Treatment Enables Hole Transport Material to Outperform Spiro-OMeTAD in Solid-State Dye-Sensitized Solar Cells (original) (raw)
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Short-term light soaking effect on dye-sensitized solar cells
Journal of Physics: Conference Series, 2019
Dye-sensitized solar cells (DSSCs) are one of the most promising third generation solar cells and have been regarded as a competitive alternative to the conventional silicon-based photovoltaic devices due to their relatively low production cost. Light soaking effect is an intriguing phenomenon that exists in DSSCs, which refers to the enhancement of the electrical parameters in the cells after being exposed to light soaking. In this paper, we report on the variation in the electrical parameters of DSSCs under continuous exposure to a simulated solar irradiation for a period up to 6h. Increments of Jsc and Voc in DSSC were observed after 6h of light soaking, which led to improved efficiency from 3.87% to 4.50%. The improvements may be ascribed to the formation of electron trapping states below the TiO2 conduction band edge, which facilitated the charge carrier transport.
The Journal of Physical Chemistry C, 2014
Push−pull" structures have been considered a winning strategy for the design of fully organic molecules as sensitizers in dyesensitized solar cells (DSSC). In this work we show that the presence of a molecular excited state with a strong charge-transfer character may be critical for charge generation when the total energy of the photoexcitation is too low to intercept accepting states in the TiO 2 photoanode. Though hole transfer to the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene can be very fast, an electron−hole pair is likely to form at the organic interface, resulting in a possible traplike excitation. This leads to poor photocurrent generation in the solid state DSSC (ss-DSSC) device. We demonstrate that it is possible to overcome this issue by fabricating SnO 2 -based ss-DSSC. The resulting solar cell shows, for the first time, that a SnO 2 -based ss-DSSC can outperform a TiO 2 -based one when a perylene-based, low-band-gap, push− pull dye is used as sensitizer. equally to this work. Figure 4. (a) Current/voltage characteristics under simulated solar conditions measured for ss-DSSC fabricated from either TiO 2 or SnO 2 nanoporous films sensitized with ID504 dye. As inset, the table reports the main figures of merit of the photovoltaic devices. (b) Photovolatic action spectra for TiO 2 -and SnO 2 -based DSSC incorporating ID504 as the sensitizer.
Materials Sciences and Applications, 2013
Light soaking characterization on complete SnO 2 :F/TiO 2 /In(OH) x S y /Pb(OH) x S y /PEDOT:PSS/Au, eta solar cell structure as well as on devices which do not include one or both TiO 2 and/or PEDOT:PSS layers has been conducted. Additionally, studies of SnO 2 :F/In(OH) x S y /Pb(OH) x S y /PEDOT:PSS/Au solar cell have been performed. The power conversion efficiency and the short circuit current density have been found to increase with light soaking duration by a factor of about 1.6-2.7 and 2.1-3, respectively. The increase in these two parameters has been attributed to the filling up of trap states and/or charge-discharge of deep levels found in In(OH) x S y. These effects take place at almost fill factor and open circuit voltage being unaffected by the light soaking effects.
Electron Lifetime in Dye-Sensitized Solar Cells: Theory and Interpretation of Measurements
Journal of Physical Chemistry C, 2009
The electron lifetime τ n in dye-sensitized solar cells (DSC) is a central quantity to determine the recombination dynamics in the solar cell. It can be measured by several methods: impedance spectroscopy, IMVS, stepped time transients, and open-circuit voltage decays. The paper aims at a better understanding of this fundamental parameter. We summarize the main models that describe the lifetime dependence on bias voltage or carrier density, and find that there are two complementary approaches to clarify the structure of the lifetime. The first is to treat the lifetime as a product of the chemical capacitance and recombination resistance. This approach is important because the resistance largely determines steady state operation characteristics of the solar cell close to open-circuit voltage. The second approach is based on a kinetic model that describes in detail the different processes governing the decay of the carrier population in a measurement of τ n . The lifetime is composed of a trapping factor and a free electron lifetime. Since the diffusion coefficient contains the reciprocal of the trapping factor, it is found that a product (diffusion coefficient) × (lifetime) reveals the shape of the free electron lifetime, which contains the essential information on kinetics of electron transfer at the surface as a function of the position of the Fermi level. A model based on an exponential distribution of surface states provides a good description of the voltage and temperature dependence of free electron lifetime and diffusion lengths in high performance DSCs.
Journal of Electroanalytical Chemistry, 2010
Electron transport in dye-sensitized solar cells with varying mesoporous TiO 2 film thicknesses was investigated using experimental and computational methods. More specifically, photocurrent transients resulting from small-amplitude square-wave modulation of the incident light were recorded for a series of solar cells, whereby the dependence of the wavelength and direction of the illumination was investigated. The responses were compared to simulations using different models for diffusional charge transport and analyzed in detail. The photocurrent transients are composed of two components: an initial fast response in case of illumination from the working electrode side, or an initial apparent delay of photocurrent decay for illumination from the counter electrode side, followed by a single exponential decay at longer times, with a time constant that is identified as the electron transport time. The initial response depends on the thickness and the absorption coefficient of the film. Transport times for different films were compared at equal short-circuit current density, rather than at equal light intensity. Experimentally, the transport time showed a power-law dependence on the film thickness with an exponent of about 1.5. Analysis using the quasi-static multiple trapping (MT) formulation demonstrates that this behavior originates from differences in quasi-Fermi level in the TiO 2 films of different thickness when equal photocurrents are generated. The Fokker-Planck relation was used to derive expressions for the electrons flux in porous TiO 2 films with a position-dependent diffusion coefficient.