Preparation Of Carbon Quantum Dots And Its Application In Dye-sensitized Solar Cells

Carbon quantum dots(CQDs), one kind of nano carbon marterial,was firstly prepared in the year of 2004 and have attracted considerable interests. Due to their great advantages of excellent fluorescent performance, low toxicity, biocompability, high stability and easy surface tuning, a series of applications, like bioimaging, ion probe, fluorescent ink, surface-enhancement raman scattering(SERS), have been developed by many researching groups. These applications have great connection with the good fluorescent property and biocompatibility while not many people use CQDs in the energy storage and energy transformation field, expecially in the field of dye-sensitized solar cells(DSSCs). Therefore, it becomes necessary for extending CQDs application and digging their full potential that suitable CQDs can be synthesized and employed to enhance DSSCs performance.Nitric acid oxidation cutting method is employed to prepare graphene quantum dots(GQDs) with plenty oxygen containing groups from graphene.The Co2+ can be absorbed to the surface of GQDs because of the electrostatic attraction which will further limit the continuous growth of CoS, resulting in the nano-sized CoS. CoS-GQDs has inherited the same structure as CoS sheet while CoS-GQDs becomes much smaller and the lamellar stacking is shown more tightly. When used as the counter electrode of DSSCs, CoS-GQDs delivers much better performance than CoS, even than Pt, with the reason of that nano-sized CoS-GQDs which can be soaked totally by electrolyte have decreased the amounts of interface between counter electrode(CE) material and electrolyte, leading to their improved catalytic activity reducing I3- to I-. The DSSCs based on CoS-GQDs can be modulated by the experimental voltage. When the voltage is set as 2 V, the corresponding CoS-GQDs-DSSCs obtain the best conversion efficiency of 7.30%.Hydrothermal treatment is applied to synthesize CQDs with high electronegativity from holly leaves and PAN-CQDs fiber is prepared successfully via blending spinning combined with carbonization technique. PAN-CQDs still well maintains the fiber structure of PAN after being added a certain amount of CQDs. Not only the fiber diameter, but also the defective area could be tuned by CQDs amounts. Evaluated as the CE material of DSSCs, PAN-CQDs gives rise to the highest conversion efficiency of 7.33% superior to Pt of 6.94% when the additon of CQDs reachs to CQDs:PAN=7.4:100(wt%) due to the smallest diameter of 130 nm and the maximum defective area.