Paper Title
Screen-Printing Electrolytes Containing TiO2 and ZnO Nanofillers for Dye-Sensitized Solar Cells

Abstract
In this study, screen-printing electrolytes are prepared by mixing poly(ethylene oxide) (PEO) and liquid-type electrolytes. By judiciously adjusting the amount of PEO, the fluidic properties of electrolytes and the thickness of resultant electrolyte layers can be controlled; more importantly, the electrolyte layer in a dye-sensitized solar cell (DSSC) can be fabricated by the screen printing for two times, thus creating a double-layered electrolyte structure. Metal oxide nanoparticles have been greatly used as the nanofillersin electrolytes to improve the performance of DSSCs; in this work, two kinds of nanoparticles are employed and investigated, i.e., TiO2 and ZnO.When the TiO2 is introduced into the electrolyte, the corresponding DSSC shows increases in both short-circuit current density (JSC) and conversion efficiency (from 8.12% to 8.55%),which isattributed tothe reduced charge transfer resistance at the electrolyte/counter electrode (CE)interface;however, the introduction of TiO2 in the electrolyte might cause concern about the desorption of dyes, which can further result in poor stability of DSSCs.On the other hand,the adoption of ZnO in the electrolyte can enhance the open-circuit voltage (VOC) of a DSSC significantly; an impedance result confirms that in such solar cell, the conduction band of the TiO2thin film is negatively shifted. But, the use of ZnO also triggers inferior charge transfer at the electrolyte/CE interface. To fully take advantage of the two nanofillers, a strategy for a DSSC including two different electrolyte layersis executed.Two kinds of DSSCs are fabricated; one is assembled by printing TiO2- and ZnO-involved electrolytes on the photoelectrode (PE) and the CE, respectively (PE/Electrolyte-TiO2/Electrolyte-ZnO/CE), and the other has a similar structure but in reverse order (PE/Electrolyte-ZnO/Electrolyte-TiO2/CE). Experimental results exhibit that the former shows photovoltaic parameters comparable to those of a solar cell without nanofillers, while the latter can display a high VOC and a low charge transfer resistance, together with a much better conversion efficiency of 8.518%. Keywords - Dye-sensitized solar cell, Screen printing,Additive, Metal oxde