Study Of Electronic Devices Based On Aqueous Two-dimensional Material Inks

Since the discovery of graphene,two-dimensional（2D）materials have shown great potential in electronic devices due to their unique physical and chemical properties.However,how to prepare 2D materials and their devices in a large-scale,low-cost and environmental-friendly manner is still a challenge for researchers.Here,aqueous 2D material inks were prepared using the novel water-based dispersant developed by our group,and a variety of electronic devices,including graphene supercapacitors,photodetectors electroluminescence（EL）devices based on graphene electrodes were fabricated either by drop-casting,spin-coating,or inkjet printing.These electronic devices were then systematically studied.The main research contents of this work are listed as follows:Firstly,by using sodium 2-hydroxy-7-naphthalene sulfonate(C₁₀H₉Na O₄S)as the dispersant,water-based dispersions of 2D materials,including graphene and transition metal dichalcogenides（TMDCs）,such as tungsten disulfide（WS₂）,molybdenum disulfide（MoS₂）and molybdenum ditelluride（MoTe₂）were obtained,followed by adjusting the rheological parameters to prepare the 2D crystal inks.The droplets in different printing modes were captured using a homemade high-speed camera shooting system.Then a variety of micro-area characterization techniques,including optical microscopy（OM）,Raman spectroscopy（Raman）,atomic force microscopy（AFM）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）,have been used to characterize the aqueous inks,demonstrating that the excellent properties of the 2D material inks obtained by this method for the subsequent study of electronic devices;After that,graphene supercapacitors were fabricated by inkjet printing of graphene inks on the flexible substrates using a mask,where the printed graphene films were used as the electrodes and the ionic liquid of sulfuric acid-polyvinyl alcohol（H₂SO₄-PVA）was chosen as the electrolyte.Then,cyclic voltammetry（CV）,galvanostatic charge-discharge（GCD）and electrochemical impedance spectroscopy（EIS）tests were carried out using the electrochemical workstation.Besides,both the graphene supercapacitors in series and in parallel were characterized.The highest calculated stack capacitance reached 5.5 F/cm³,and the maximum energy density and power density could reach 0.763 m Wh/cm³ and 390 W/cm³,respectively.Next,the EL devices which were consisted of the patterned graphene electrodes,the light emitting layer and dielectric layer,have been fabricated.The patterning process of graphene electrodes was achieved by drop-casting of graphene inks using a homemade mask,which was obtained by a micro plane cutting machine.The luminescence wavelength between 450 to 550nm of the EL devices at 120 V and 3 kHz was characterized using a spectrometer and a variable voltage source,which was composed of a signal generator and a voltage amplifier.The luminance of the EL device at different voltages and frequencies,as well as the devoice stability were tested,which showed a maximum luminance of 500 cd/m² at 200 V and 3 kHz.and a decrease in intensity by 10%after 500 times of deformation;Finally,combined with aqueous TMDCs inks and chemical vapor deposition（CVD）graphene,the photodetectors based on the TMDC/graphene vertical heterostructure were prepared by inkjet printing and the performance was optimized with a high responsivity up to2.5A/W.For comparison,the photodetectors based on CVD TMDC/graphene vertical heterostructure were fabricated by the transfer stacking method.Currently,the photo-responsivity of the device was still below 0.1 A/W,which was far inferior to the device prepared by aqueous TMDCs inks,presumedly due to the organic contaminations introduced during the transfer process for CVD TMDCs,as well as the higher thickness of the TMDCs films prepared by 2D TMDC inks.