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“Background Dye-sensitized solar cells (DSSCs) are attracting attention globally because of their

low cost, high energy Fer-1 conversion efficiency and potential applications [1–4]. Graphene has been extensively utilized in organic photovoltaic (PV) cells owing to its excellent optical and electrical characteristics, which are exploited in transparent conductive films or electrodes [5–8]. Some researchers have reported on composite graphene-TiO2 photoelectrodes in DSSCs [9–12]. Fang et al. [9, 10] discussed the effect of the amount of graphene on the structures and properties of DSSCs. DSSCs with the optimal composite TiO2 film can achieve a photoelectrical conversion efficiency of 7.02%. Graphene is also commonly PKC412 manufacturer used in graphene-based counter electrodes in DSSCs [13–15]. The conventional counter electrode is platinum (Pt) because of its outstanding conductivity, catalytic activity, and stability when in contact with an iodine-based electrolyte. The expensive Pt can be replaced with graphene films in DSSCs without significantly sacrificing photoelectrical efficiency.

This replacement can simply reduce the cost of the fabrication process [13]. Zhang et al. [14] grew DSSCs with graphene-based counter electrodes, which exhibited a photoelectrical conversion efficiency of as high as 6.81%. Double-layer photoelectrodes have been used to increase the photoelectrical conversion efficiency of DSSCs. Many investigations have focused on modifying the nanostructures of TiO2 photoelectrodes ARRY-162 to nanospheres, nanospindles, nanorods, nanowires, and others [16–20]. Many special nanostructures of photoelectrodes can increase ioxilan the scattering of light and improve the performance of DSSCs [16, 17]. This work develops a new TiO2/graphene/TiO2 sandwich structure for photoelectrodes. A thin layer of graphene was inserted into the traditional TiO2 photoelectrode layer, making it a double layer. DSSCs with the traditional structure were also fabricated and the characteristics

of the prepared DSSCs were compared. The DSSC with the TiO2/graphene/TiO2 sandwich structure exhibited excellent performance and higher photoelectrical conversion efficiency. This improvement is associated with the increase in electron transport efficiency and the absorption of light in the visible range. Methods Preparation of TiO2 photoelectrodes The TiO2 slurry was prepared by mixing 6 g of nanocrystalline powder (P25 titanium oxide; Evonik Degussa Japan Co., Ltd., Tokyo, Japan), 0.1 mL Triton X-100, and 0.2 mL acetylacetone. The slurry was then stirred for 24 h before being spin-coated on ITO glass substrate at a rotation rate of 2,000 or 4,000 rpm. Following the deposition of graphene, the above procedure was carried out in the fabrication of DSSCs with the TiO2/graphene/TiO2 sandwich structure. The as-prepared TiO2 photoelectrodes were dried and annealed at 450°C for 30 min.