Synthesis Of Graphene Quantum Dots And Their Applications In Organic Electronic Devices

In comparison with semiconductor quantum dots, graphene quantum dots (Graphene Quantum Dots, GQDs) have advantageous features including chemical stability, low cytotoxicity and unique fluorescent properties. With these outstanding properties, GQDs has demonstrated enticing application prospects in the field of biological imaging, electrochemical sensing, catalysis technology etc. Its research concerns the practical meaning and value like environmentally friendly, resource-saving, portable and others.Currently research is blooming over the globe in GQDs; there are challenges ahead in synthesis as well as processing of GQDs leads to uncontrollable fluorescence, difficulty in size distribution, poor stability. The goal of this thesis is selecting appropriate carbon source to prepare GQDs with stable fluorescence, high yield rate and application of GQDs in organic solar cells and organic storage devices to achieve higher performance devices. The main conclusions are shown as follows:A. GQDs material with blue fluorescence emission dissolved in chlorobenzene was successfully prepared. By using chemical solution method, we open and crop the DWNTs under the conditions of magnetic stirring and heating to obtain graphene nanosheets with sizes ranging from 10nm to 100nm. After separation and extraction process we obtain the desired GQDs and its main characterization results are as follows:size of less than 10nm, lattice fringes, the thickness of 2-3nm, with a strong blue fluorescence emission spectrum, the fluorescence spectrum dependency of excitation wavelength and excellent size-dependent fluorescence lifetime characteristic.B. Preparation of organic solar cells with high energy conversion efficiency based on the active layer of three architectures system with GQDs was studied. By introducing GQDs to the classic organic solar system of P3HT:PCBM, absorption spectra of the device was improved and the absorption peak exhibits trace of red shift. The energy conversion efficiency of organic solar cell reached 4.35%. By adjusting the ratio of PCBM to optimize the device performance, it was found that when the ratio of PCBM was 0.6, the device reached higher energy conversion efficiency of 5.24%. PTB7:PC71BM introduced GQDs to the new system of PTB7:PC71BM to get the device with energy conversion efficiency up to 6.6%. And it was found that the concentration of GQDs can be improved to enhance current density of devices.C. By introducing GQDs, flexible memory device with superior performance was prepared and this study has a certain value in the high density storage devices. Fabrication of flexible memory device based on functional layer with PMMA:GQDs was performed and it was found that the ON/OFF ratio is up to 103. The device performs essentially the same as before after bending several times. The device based on functional layers with PVK:GQDs exhibits low drive power consumption and stable bistability. After nearly thousand times’ scanning, the device with laminated structure of PI/GQDs/PI still has a good resistance degeneration, which has significance for the realization of multi-level cell.In summary, by combining theory and experiment this work presented the preparation of graphene quantum dots with stability, uniform particle size and excellent fluorescence properties in scientific methods. And its skillful application in organic solar cells and organic storage devices also performed to obtain the electronic devices with excellent performance and stability. Thus, this thesis has some innovative and practical value to a certain extent.