Study Of Graphene Quantum Dots Film And Devices By Solution Processing Methods

Organic heterojunction solar cells have been considered as next generation solar cells,but mobility of bulk heterojunction materials is poor and efficiency is low. People have been trying to improve the performance of devices. Graphene quantum dots(GQDs) is a kind of zero-dimensional graphene nanomaterials, which has the features of graphene and quantum dots, unique quantum confinement and edge effects resulting in exceptional fluorescence properties and up-conversion luminescence properties. It is promising to apply to optoelectronic devices. The band gap of graphene quantum dots is tunable and its large surface area can improve the efficiency of optoelectronic devices. So mixing GQDs to heterostructure materials is expected to improve the performance of solar cells. But the luminescence mechanism of graphene quantum dots is not clear, so the research in the field is still in its infancy.The thesis first studied the main preparation methods and applications of GQDs, then simply studied the working principle and main parameters of solar cells. The main research contents were as follows:Firstly, the graphene oxide films were prepared and characterized. Graphene oxide was the precursor for the preparation of graphene quantum dots. In this paper, we prepared graphene oxide by improved Hummers method; it was identified in three independent steps:low temperature, medium temperature and high temperature reaction stages. The results of FT-IR, AFM and XRD characterization showed that GO had a lot of oxygen-containing functional groups, the inter-planar spaces of graphene oxide was 8.03 ?.Secondly, the preparation and characterization of graphene quantum dots were investigated. GQDs were prepared by solvothermal method. Graphene oxide(GO) was as the precursor and was diffused in organic solvents after ultrasonicing. Then the suspension was transferred into a poly(tetrafluoroethylene)(Teflon)-lined autoclave(50 mL), in which GO was heated up, bridge oxygen functional groups of GO were broken to get smaller size of GQDs.Thirdly, mixed graphene quantum dot solar cells were investigated by solution-processing method. GQDs were doped to P3HT: PCBM system. The influence factors were investigated on performance of the device, such as doping concentration of GQDs, reduction of GQDs and annealing of the device. Doped GQDs could improve the short-circuit current of the device, and the best doping concentration was 0.15 wt.%,short-circuit current was 2.29 mA/cm2; doped reduced GQDs could improve the fill factor of the device, from 31.57% to 40.80%.