Preparations And Researches Of Novel Counter Electrodes For Dye-Sensitized Solar Cells

Dye-sensitized solar cells ?DSSCs? have attracted great attention due to its properties of high photoelectrical conversion efficiency, low cost, and easy fabrication. The counter electrode ?CE? is an important part of DSSCs, whose catalytic ability, conductivity and stability greatly influence the photovoltaic performance of DSSC. The platinum ?Pt? has been used as the counter electrode because of its good catalytic activity and high conductivity. However, both of its low reserves and high price has limited Pt as the counter electrode for large scale applications. Moreover, Pt would corrode in the T/I3- electrolyte and turn into PtI4 or H2PtI6-To explore the novel electrode materials with low price,good stability and excellent photoelectric performance, we try to combine graphene with metal selenides and apply the composites to the CE of DSSC. The main contents and results of the research include as follows:?1? Graphene oxide ?GO? is synthesized by using an improved Hummer's method, and reduced graphene oxide ?rGO? is loaded on the conductive glass FTO by a spinning method as the counter electrode ?CE? of dye-sensitized solar cell. Scanning electron microscopy ?SEM? and transmission electron microscopy ?TEM? show the surface of obtained graphene has a lot of distinct wrinkles, which can increase the contact area with electrolyte. By analyzing electrochemical impedance parameters of the graphene CE and the platinum CE, we find that the catalytic ability of pure graphene CE is inferior to Pt CE in I-/I3-electrolyte. The photoelectric conversion efficiency of graphene-based DSSC is 5.24%, which is 61.5% of Pt-based DSSC.?2? FeSe₂/rGO composites are synthesized by a hydrothermal method, and are applied in DSSCs as the material of CE for the first time. X-ray diffraction ?XRD? analysis shows that the synthesized FeSe₂ is pure phase, SEM and TEM photographs show FeSe₂ nanorods are successfully loaded onto the surface of graphene, and FeSe₂ nanorods has a clear lattice fringes, indicating FeSe₂ has a high degree of crystallization. Cyclic voltammetry ?CV?, electrochemical impedance ?EIS? test, Tafel tests indicate that FeSe₂/rGO CE has both high conductivity and good catalytic ability, whose electrocatalytic ability towards I3- is better than Pt, FeSe₂ and rGO CE in the T/I3- electrolyte. Photocurrent density-voltage ?J-V? curves show that the photoelectric conversion efficiency of DSSC using a FeSe₂/rGO CE has reached 8.90%, which has improved 4.46% compared to the DSSC using a Pt CE. Continuous cyclic voltammetry curves manifest that FeSe₂/rGO CE has a better stability than Pt CE in I-/I3- electrolyte.?3? NiSe₂/rGO composites are synthesized by a hydrothermal method, and NiSe₂/rGO conductive film on FTO is prepared by spin coating. SEM photographs show that NiSe₂ shape like nanospheres, further analysis by TEM photograph manifests that NiSe₂ nanospheres are composed of nanoparticles. NiSej/rGO composites has a mesoporous structure because that NiSe₂ nanospheres and nanoparticles increases the distance between the graphene sheets, which greatly increases the contact area between NiSe₂/rGO CE and I-/I3- electrolyte. According to the electrochemical test of different counter electrodes and photovoltaic performance of DSSCs, we find that NiSe₂/rGO CE has the lowest peak to peak potential difference and the lowest charge transfer resistance ?R&? in I-/I3- electrolyte, compared to the Pt CE, pure graphene CE and NiSe₂ CE. At the same time, the photoelectric conversion efficiency of NiSe₂/rGO-based DSSC has reached 9.00%, which is higher 5.63% than Pt-based DSSC.