Theoretical Study On Graphene-based Counter Electrode Of Dye-sensitized Solar Cells

Dye-sensitized solar cell(DSSC)has received considerable attention as a promising new-generation solar cells in recent years owing to its low cost,environmental friendliness and easy production.The electrochemical performance of DSSC is directly determined by the quality of the counter electrode.As a traditional electrode material,platinum nano-materials are widely used.However,the high cost and limited availability of platinum have restricted the large-scale commercial application of DSSCs.Therefore,it is necessary to search for alternative counter electrode materials with relatively low cost,high conductivity,and excellent catalytic activity to replace the traditional platinum material.Graphene,as one of the hottest star materials,has attracted extensive attention due to its unique two-dimensional plane structure,special single atomic layer,as well as rich properties of this material.Because of its resiliance,strength,thermal,electrical,optical and other properties,graphene materical can be used in many areas,such as aerospace engineering,physics,chemistry,materials,telecommunications,computer science.Recently,many experimental groups reported the synthetise and application of graphene-based counter electrode materials which exhibit high electrocatalytic efficiency.In present paper,the density functional theory is used to perform quantum chemical calculations for the doping effect and adsorption behaviors of pristine graphene and N or/and S doped graphene materials.The calculations explain the experimental restults very well,and also provide further insight for screening and development of promising electrode materials for DSSC.The main results and conclusion are as follows:Using the B3LYP method and Gaussian package,the NBO atomic charge density distributions are calculated based on the fragment model of graphene and the N or/and S doped graphene.It shows that more active sites with positive charge are produced by N or S doping.The N/S co-doping induces a synergistic effect by producing more active sites with bigger positive charge and thus enhances the electrocatalytic activity of the counter electrode material.Using the PBE functional and VASP program,based on the periodic model of graphene series,the adsorption behaviors of pristine graphene and N or/and S doped graphene for I2 were studied in detail.The calculations for the adsoption energy,adsorption sites,charge transfer,and band structures show that the N/S codoped graphene has stronger adsorption ability for I2 than that of N or S monodoped graphene.The BADER charge analysis also revealed the synergistic effect by co-doping with N and S atoms.Based on both of the fragment or periodic graphene series models,the theoretical calculations come to the same conclusion.The doping of nitrogen and sulfur atoms in graphene leads to the formation of more active sites,which contribute to the adsorption upon I2.Furthmore,the N/S co-doping produces synergistic effect to improves the electrochemical performance of the graphene-based electrode material.