Influence of the Adsorption of Phycocyanin on the Performance in DSS Cells: and Electrochemical and QCM Evaluation

Jean-David Décoppet, Michael Graetzel, Thomas Moehl
2016
Journal paper

Abstract

The influence of some coadsorbents and different pH values on the efficiency of DSS cells assembled with phycocyanin was evaluated using quartz crystal microbalance (QCM) and electrochemical techniques as impedance spectroscopy (EIS) and cyclic voltammetry (CV). Chlorophyll, heptadecanoic acid and 7.5 or 8.5 pH values were applied when nanostructured TiO2 electrode was dipped in the dye solution. Best efficiency conversion values were obtained when using fatty acids as coadsorbents, reaching a conversion efficiency of 0.04 % for open cells.

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Dye-sensitized solar cells with power conversion efficiencies of up to 6.5% have been fabricated using a cobalt trisbipyridyl redox mediator with the cis-diisothiocyanato-(2,2'-bipyridyl-4,4'-dicarboxylic acid)-(2,2'-bipyridyl-4,4'-dinonyl) ruthenium(II) (Z907) sensitizer. This represents a significant improvement in efficiency compared with previous reports using ruthenium sensitizers. In situ near-IR transmittance measurements in conjunction with electrochemical impedance spectroscopy have been used to explain the difference in performance between DSCs using Z907 and another benchmark sensitizer cis-diisothiocyanato-bis(2,2'-bipyridyl-4,4'-dicarboxylic acid) ruthenium(II) bis(tetrabutylammonium) (N719). It is found that the small-perturbation electron diffusion length (L-n) is significantly longer in Z907 cells compared with that in N719 cells, which can explain most of the difference in performance. It is also shown that the longer L-n in Z907 cells is caused by inhibited recombination, as opposed to faster transport, and possible reasons for this are discussed. Our methodological approach is especially useful for accurately determining L-n when it is shorter than the TiO2 layer thickness, where standard dynamic techniques start to become unreliable.

American Chemical Society2011

Effect of Sensitizer Adsorption Temperature on the Performance of Dye-Sensitized Solar Cells

Pascal Comte, Jean-David Décoppet, Michael Graetzel, Mohammad Khaja Nazeeruddin, Peng Wang, Shaik Mohammed Zakeeruddin, Min Zhang

Employing a mesoscopic titania photoanode whose bilayer structure was judiciously selected to fit the optoelectronic characteristics of the Ru-based heteroleptic complex Na-cis-Ru(4,4'-(5-hexyltiophen-2-yl)-2,2'-bipyridine)(4-carboxylic-acid-4'-carboxylate-2,2'-bipyridine)(thiocyanate)(2), coded as C101, we investigated the effect of temperature for dye adsorption on the photovoltaic performance of dye-sensitized solar cells (DSCs). We found a significant efficiency enhancement upon lowering the temperature applied during the sensitizer uptake from solution. When the dye adsorption was performed at 4 degrees C, the photovoltaic performance parameters measured under standard reporting conditions (AM1.5 G sunlight at 1000 W/m(2) intensity and 25 degrees C), i.e., the open circuit voltage (V-oc), the short circuit photocurrent density (J(sc)), the fill factor (FF), and consequently the power conversion efficiency (PCE), improved in comparison to cells stained at 20 and 60 degrees C.Results from electrochemical impedance spectroscopy (EIS) and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) show that the self-assembled layer of C101 formed at lower temperature impairs the back-electron transfer from the TiO2 conduction band to the triiodide ions in the electrolyte more strongly than the film produced at 60 degrees C. Profiting from the favorable influence that the low-temperature dye uptake exerts on photovoltaic performance, we have realized DSCs showing a power conversion efficiency of 11.5%.

2011

Influence of the counter electrode on the photovoltaic performance of dye-sensitized solar cells using a disulfide/thiolate redox electrolyte

Julian Burschka, Michael Graetzel, Mohammad Khaja Nazeeruddin, Shaik Mohammed Zakeeruddin

Strong scientific interests focus on the investigation of iodine-free redox couples for their application in dye-sensitized solar cells (DSCs). Recently, a disulfide/thiolate-based redox electrolyte has been proposed as a valuable alternative to the conventional I-3(-)/I- system due to its transparent and non-corrosive nature. In the work presented herein, we systematically studied the influence of different counter electrode materials on the photovoltaic performance of DSCs employing this promising organic redox electrolyte. Our investigations focused on understanding the importance of electrocatalytic activity and surface area of the electroactive material on the counter electrode, comparing the conventional platinum to cobalt sulfide (CoS) and poly(3,4-ethylenedioxythiophene) (PEDOT). Electrochemical Impedance Spectroscopy has been used to study in detail the interfacial charge transfer reaction at the counter electrode. By using a high surface area PEDOT-based counter electrode, we finally achieved an unprecedented power conversion efficiency of 7.9% under simulated AM1.5G solar irradiation (100 mW cm(-2)) which, to the best of our knowledge, represents the highest efficiency that has so far been reported for an organic redox couple.

2012