Prepartion And Characterization Of Tungsten Disulfide Counter Electrodes For Dye-sensitized Solar Cells

With the development of economy and social, energy issues have been the core problem of sustainablehuman development. Due to the depletion of fossil energy and greenhouse which is translated into globalclimate changing, solar energy as environmentally friendly energy that converts solar energy to electricitydirectly has attracted our eyes. In the past decades, DSSC has been one of the favourite topics of energyresearch between countries. Since1991, Michael Gr teal and Brian O’Regan invented dye-sensitized solarcells (DSSC). DSSC are expected to provide better properties of the sample preparation process, low cost,high conversion efficiency etc.Dye-sensitized solar cells are typically consisted with working electrode which is dye-sensitized withTiO2, an electrolyte and counter electrode made with Pt. Pt as a precious metal is not the best chance for theindustrial development of dye-sensitized solar cells because of its expensive price and rare. In previousstudies, many kinds of materials have been studied to substitute Pt, such as carbon materials, CoS, WC andsome conductive polymer materials and so on.In our earlier work, we found WS2show high catalytic activity in the redox reactions at counterelectrodes of DSSC. In addition, with the inferior conductivity, WS2as counter electrodes have low filledfactor,so it is important for us to improve the performance of WS2. In the present work, we study thecounter electrodes material made with WS2and MoS2.The preparation process of WS2and MoS2filmsfollowed methods of lithium-ion batteries. The paper includes the following sections:First, it features the development of solar cells and describes dye-sensitized solar cells principlesbriefly. This section also introduces the purpose and significance of this project.Second, experimental methods and instrumentation principles were described.Third, it will simplify the best ratio between materials in the preparation process of WS2as counterelectrodes. WS2is invoked as active materials for the DSSC counter electrode. The ratio between thevarious materials (such as the active material, acetylene black, PVDF, et al.) used for the counter electrodewas optimized. The WS2counter electrode showed the best performance When the mass ratio of dynamicmaterials, acetylene black and PVDF were7:1.5:1.5. Under such condition, the short-circuit current density(Jsc), open circuit voltage (Voc), fill factor (FF) were15.18mAcm-2,0.64V and0.67, respectively. As a consequence, the power conversion efficiency of the DSSC (5.48%)was a litter low which was comparablewith that of the DSSC assembled with a Pt counter electrode (6.6%). But it demonstrate that the WS2is ahypothetical functional material for the counter electrode of DSSC as well. Of course WS2as counterelectrodes material still require further optimization.Forth, we prepared carbon-coated electrodes for WS2using a straightforward method. Under optimalconditions, the total power conversion efficiency of WS2carbon-coated electrodes was5.5%. The flexiblephotocathode was working on ITO (indium tin oxide)/PEN (polyethylene naphthalene) which showed anoverall power conversion efficiency of5.02%under one sun illumination. This is necessary to demonstratethat the WS2electrode coated with carbon is a very promising material alternative to the Pt electrodematerial.Fifth, we investigated that MoS2was used only for the counter electrode of DSSC. At the samecondition, the power conversion efficiency of MoS2counter electrode was3.49%while the WS2counterelectrode was4.39%.Due to its short-circuit current density and open circuit voltage is lower than WS2, thepower conversion efficiency of MoS2is lower too. We just have preliminaries exploration of pure MoS2material, if the preparation condition of MoS2were optimized, the DSSC performance would need to beimproved significantly.Sixth, it is the summary and outlook of our studies.