Controllable Synthesis Of Silver Nanowires And Research On Their Optoelectronic Properties Of Composite Electrodes

Transparent electrodes,as an important part of optoelectronic devices,have a wide range of applications,especially in the use of organic light-emitting diodes,display panels,touch screens,and solar cells,and being one of the emphases for researchers.With a rapid development of electronic products and the corresponding manufacturing techniques,indium tin oxide(ITO)as a traditional transparent electrode material,has been limited for its wide applications due to its indium deficiency,high manufacturing cost,and poor flexibility.Therefore,there is an urgent need to find new alternatives.Among many new types of transparent electrode materials,silver nanowire transparent electrodes have many advantages including its excellent conductivity,high light transmittance,high flexibility,and simple green fabrication process.It also accords with the trend of low-cost and bendable development for electronic products,to be an ideal alternative for ITO transparent electrodes.It is well known that the aspect ratio of nanowires greatly influences the electrode characteristics of transparent electrodes.However,there are still many issues in the synthesis process such as difficult control of the aspect ratio,poor repeatability,harsh reaction conditions,and cumbersome operation procedures.In addition,the silver nanowire transparent electrode itself also has many disadvantages of high contact resistance,weak oxidation resistance,poor adhesion,constraining the industrialization process.Various strategies have been proposed to address these issues.The welding induced by thermal or light,pressure or plasmon,can effectively reduce the junction resistance,without an attenuation of the light transmission.However,it brings some side effects,such as partial oxidation,to a certain degree of damage to the device.In addition,the performance of the electrode can be effectively improved by constructing a composite,such as AgNWs/PEDOT: PSS,AgNWs/ZnO,AgNWs/AZO,and so on.It can not only protect the silver nanowire,improving its stability,but also fill the voids effectively,increasing the adhesion to adjacent layers and the carrier transmission.However,there are various problems in this way,such as the weak anti-oxidation and corrosion resistance of PEDOT: PSS,poor flexibility and film-forming ability of ZnO,and so on.Thus,a new approach needs to be explored to comprehensively improve the adhesion,stability,and conductivity without reducing the light transmittance and electrical conductivity.Aiming for solving the above issues,this dissertation focuses on the controllable synthesis and applications of silver nanowires.Firstly,by the steric hindrance effect of PVP molecular chains and the chemical cationic properties of the additives,a modified traditional polyol reduction process was elaborately designed,for the synthesized AgNWs with contronllable lengths and diameters.The synthesized AgNWs were further employed in a CIGS thin-film solar cell,which breaks the limitation of pristine silver nanowires have low efficiency in CIGS-based photovoltaic devices,achieving a champion efficiency of 4.97%.Furthermore,to address the issues of poor stability of silver nanowires and poor adhesion to the adjacent layer,a combination of junction welding and protective layer introducing,was proposed to achieve the goal to further improve the efficiency of CIGS photovoltaic devices.The specific research contents are as follows:1.Controllable synthesis of AgNWs with a high aspect ratioSimple and reliable solvothermal method was used to control the preparation of silver nanowires through a modified polyol reduction process.The steric hindrance effect of the surfactant polyvinylpyrrolidone(PVP)molecular chains and cationic chemical characteristics were mainly explored on the effect of morphological evolution.By using the interpenetration effect of long and short chains of PVP,two different molecular weight PVPs were introduced to form a protective layer induced by steric hindrance on the {100} plane to allow the selective growth of silver nanowires.Thus,silver nanowires with an aspect ratio of up to 1000 were successfully obtained.For the first time,the effect of the cationic chemical characteristics of the chloride control agent on the Ag morphological evolution has been proposed and investigated in detail,which provides a possibility for the wide applications of AgNWs-based high-performance.2.The construction of silver nanowire transparent electrode and its application in CIGS photovoltaic devicesFirstly,the AgNWs went through a selective sedimentation with acetone to increase their purity,washed with ethanol to remove the PVP coated on the surface,and finally dispersed in ethanol to make silver nanowire inks.Secondly,silver nanowire transparent electrode was constructed by a spin coating method,with a uniform distribution of square resistance,high light transmittance,and good conductivity through the precise adjustment of the coating conditions such as rotation speed,spin coating times,and ink concentration.It was further applied to CIGS-based photovoltaic devices,which achieved a highest efficiency of 4.97% compared with that of the previously reported pure silver nanowire electrodes.3.Optimization of silver nanowire transparent electrode and its effect on photovoltaic performanceThe interaction between halide ions and dissolved oxygen molecules is used to chemically weld the junctions with NaCl salt solution to reduce the junction resistance.Sequentially,a protection layer of chitosan,which is one of the most biocompatible,degradable,environmentally friendly non-toxic natural polymers,along with its excellent ability to resist oxidation corrosion,good film formability,and high transparency,was introduced.An AgNW-NaCl-Chi composite electrode was constructed to solve the problems of weak adhesion of the silver nanowires to the bottom and its own poor thermal stability and weak oxidation resistance,to achieve the optimization of the silver nanowire transparent electrode.Finally,through the double optimization of junction welding and construction of composites,the efficiency and stability of CIGS photovoltaic devices were further improved.