Study On The Preparation And Performance Of Organic Bistable Devices Based On Graphene Quantum Dots

In recent years,organic bistable devices have been widely studied as their hold promise for potential applications in next-generation flexible and transparent electronic devices.For bistable devices,suitable charge trapping materials were very important.Graphene quantum dots(GQDs)were potential suitable candidate as charge trapping material due to their low toxicity and high chemical stability.In this work,synthesis of GQDs and their application in organic bistable devices were studied.The optical and electrical performances of the devices were studied.The electron transport mechanisms were proposed to explain the effect of GQDs embedded in dielectric layers,which caused the bistable performance of the device.The main conclusions are shown as follows:Firstly,synthesis of GQDs was studied.By using hydrothermal method,double-walled carbon nanotubes were cut up and then purified by dialysis and centrifugation to obtain GQDs solution.The size of GQDs was 2-5 nm with an average thickness of 0.7 nm.GQDs showed strong green fluorescence excitation and fluorescence spectrum dependency of excitation.Subsequently,the organic bistable device with embedded GQDs in polymethylmethacrylate(PMMA)layers was fabricated on transparent indium-tin-oxide(ITO)coated polyethylene terephthalate(PET)substrate.The average transmittance in the visible wavelength range of the fabricated device was about 81.68%with the turn on voltage(VON)was-1.8 V,and the erase voltage(VOFF)was 2.7 V.The ratio of high current state to low current state was up to 104.The possible electron transport mechanisms through the fabricated device were proposed as Schottky emission,Poole-Frenkel emission and space-charge-limited-current based on the obtained current-voltage(I-V)electrical characterization.The device demonstrated promising stability with a distinct ON/OFF ratio of 104 up to 104 s and reprogrammable more than 1000 times.Even though GQDs embedded in PMMA layers shows promising bistable memory behavior,however,in real application,polymer with high thermal stability would be preferable as PMMA could be decomposed about 200 ?.Hence,the excellent thermal stability and attractive mechanical hardness hybrid organic-inorganic polymers,i.e.polymethylsilsesquioxane(PMSSQ)was chosen as dielectric layers in the subsequent study.The device was constructed on ITO coated polyethylene terephthalate to fabricate transparent and flexible organic bistable device.The average transmittance in the visible wavelength range of the device was measured 82.95%with VON about-0.9 V and VOFF was 2.2 V.The ratio of high current state and low current state was up to 104.The probable electron transport mechanisms through the fabricated bistable device were direct tunneling and space-charge-limited-current based on the I-V electrical results.The device also demonstrated promising stability with a distinct ON/OFF ratio of 104 up to 104 s without significant degradation and reprogrammable more than 1000 times.In addition,the device showed the stable hysteresis window without obvious degradation upon bending under different curvature radii.In summary,the preparation and performance of organic bistable devices based on GQDs were studied.To optimize the performance of the device,PMSSQ was chosen as dielectric layers instead of PMMA,which has excellent thermal stability and attractive mechanical hardness.The fabricated device utilizing hybrid nanocomposites consisting of GQDs sandwiched between PMSSQ layers hold promise for potential applications in next-generation flexible and transparent non-volatile memory.