Study Of Graphene Optimized Dye-sensitized Solar Cells

Dye-sensitized soalr cells (DSSCs) have attracted much attention for their advantages of such as the simple making processes, the low cost, the short energy pay-back time, the non-toxicity to the environment, and so on. On the other hand, the two dimensional material graphene has also obtained many focuses. To make use of the good properties of graphene such as conductivity and the high specific area etc, as well as the special optical properties and energy band structures of graphene quantum dots, one can apply them in the DSSCs, and prepare DSSCs optimized by graphene-based materials. This is also one of the hot-spot for the researchers. In this dissertation, we developed our research based on the preparations of materials and got the corresponding results as follows:(1) The preparation of graphene-P25composite photoelectrodes. By the simple ball-milling method, and using the graphene oxide (GO) and the commercial titanium dioxide (P25) ad the resources, we exploited the optimum ratio of GO to P25, made the graphen-P25composite photoelectrodes with good properties and applied them in the DSSC, which finally a DSSC with enhanced performances was obtained. Comparing to the photocurrent conversion efficiency of P25-based DSSC, the photocurrent conversion efficiency of DSSC used the optimum G-P25as the photoelectrode was increased by20%, which the enhancement can be attributed to the increased specific area after the annealing of GO and the good conductivity of graphene. This work made a good foundation of the usage of graphene in the DSSCs.(2) The preparation of graphene-TiO2composite photoelectrodes and the improved properties in the DSSC. Graphene-composited TiO2photoelectrodes are prepared by hydrothermal method. The influences of different amount of graphene on the structures and properties of the dye-sensitized solar cells (DSSCs) are studied and an optimal graphene-composited DSSC is obtained. Studies indicate that compositing of graphene can effectively enhance the open circuit voltage, short circuit current density, and photoelectric conversion efficiency (?) of the DSSCs. Furthermore, the ? of the DSSC with the optimal graphene-composited TiO2film is7.02±0.06%, significantly higher than that of the pure TiO2DSSC. These improvements can be attributed to the increased dye absorption due probably to the increase of the photoelectrode films'specific surface area and the good conductivity of graphene. (3) The preparation of graphene quantum dots (GQDs) and their application in the DSSCs. GQDs possess a special optical property.Graphene quantum dots (GQDs) optimized TiO2photoanodes and their dye-sensitized solar cells (DSSCs) were successfully demonstrated in this study for the first time. The characteristics of GQDs were confirmed by Raman and TEM measurements. Study indicated that the amount of dye-adsorption decreased firstly and then increased as the increase of the GQDs in the photoanodes, while that the JSc, Voc and ? of the corresponding DSSCs increased firstly and then decreased. Of all the DSSCs, the DSSC with an optimal amount of GQDs had the best performance with a minimum dye-adsorption while the maximum Jsc of14.07±0.02mA cm-2and ? of6.10?0.01%, higher than those of the conventional DSSC without GQDs by30.9%and19.6%, respectively. The minimum dye-adsorption while the maximum Jsc and ? obtained in the optimal DSSC are mainly attributed to the unique photoexcitation response of GQDs and the hot electrons injection from GQDs into TiO2. This study indicates that not only the properties of DSSCs can be improved by GQDs, but more importantly, the reduced use of dye by using GQDs is of significant importance for low cost and environment-friendly DSSCs.