The Printing And Properties Of Flexible Inorganic Semiconductor Films

Flexible printing technology provides the possibility for large-scale and low-cost production of foldable,portable,and mechanically durable electronic devices.Therefore,it has received a growing amount of attention in both academia and industry.Some materials commonly used in flexible printing are metals,carbon nanotubes,graphene,and organic compounds.Since they are relatively soft,they could be easily prepared into inks and combined with flexible substrates to produce flexible electronics.As the research moves along,some inorganic semiconductors could also be used to prepare flexible electronic products with printing technology.However,there are still a number of challenges coming in the way.First,because the chemical bond of inorganic semiconductor has high directivity,the flexibility of current inorganic semiconductor devices is unsatisfactory.To adapt to the complex geometric curves of the human body and meet the requirements of wearable electronics and the Internet of Things,inorganic semiconductors products with more excellent mechanical flexibility should be developed.This dissertation adopts the design idea of preparing ink and preparing it as thin film on flexible substrate by printing and annealing.According to the above idea,copper selenide nanoparticles were prepared by hydrothermal method.Then,Ethylene glycol was added to copper selenide to prepare ink.Finally,flexible inorganic semiconductor composite films were prepared by coating and annealing.The produced film can endure 10,000 bends at a bending radius of 5 mm and with a small amount of mechanical damage.The resistance only increased by 50%.This degree of flexibility was comparable to silver,making it a breakthrough in the study of large-size flexible inorganic semiconductor films.In addition,the mechanism of the film flexibility was explored in detail both experimentally and theoretically.It is concluded that the flexible substrate could inhibit strain localization of the composite film so the film can deform uniformly and not easily be broken,which lays a solid foundation for the preparation of the flexible film.Second,although there are studies on the fabrication of flexible inorganic semiconductor thin films using printing,most of them only focus on inkjet printing and transfer printing technology.Screen printing,which is suitable for large-scale production,is rarely used in the production of flexible inorganic semiconductor products.Also,most inorganic semiconductor samples are prepared using plastic substrates,such as PEN,PET and PI.The application of these substrates may bring about environmental problems.Environmentally friendly materials like paper and fabric are less frequently used as substrates,as they are less capable of withstanding high temperature.This dissertation made different types of inorganic semiconductor materials into uniform and stable inks,then prepared flexible films on fabrics(fibres and silks)using screen printing and annealing.These substrates used in this research were suitable for wearable electronics and environmental protection.Since the capillary force and roughness of the fabric surface were not suitable to printing continuous patterns,we modified the surface with glue to improve the resolution of patterns.The resistance of the prepared composite film only increases by 38%-156%of the initial value when bending at a radius of 3 mm for 100,000 times.In short,the scheme can be patterned on fabric to prepare inorganic semiconductor films with excellent flexibility.It is easy to operate and suitable for large-scale production.Third,current applications of flexible inorganic semiconductors on thermoelectric generator and high-level information encryption are still limited.Therefore,further research in these two fields will bring new light to the development of flexible electronics.To further expand the application of flexible inorganic semiconductors in these fields,this dissertation measured the thermoelectric(TE)properties of the previously prepared films,and selected silver selenide with good performance for further optimization.The TE film,which showed excellent thermoelectric properties,good flexibility,and the capability to be patterned,were prepared on paper by screen printing and annealing.The power factor(PF)of the film is 3250.9μW/m·K~2 at 400 K,which is approaching the highest silver selenide PF value ever reported in the literature(3500μW/m·K~2).Furthermore,the film shows excellent flexibility.Its resistance value change was smaller than 1%under repeated bending.In short,flexible silver selenide film was prepared by hydrothermal method,screen printing and annealing.T his scheme is simple and environmentally friendly,suitable for large-scale industrial production,and fully meets the requirements of wearable electronics and Internet of Things.Finally,the dissertation expands the application of inorganic semiconductor thin film in paper information security.Carbon quantum dots were synthesized,and their basic properties were studied,including fluorescence properties,stability and biotoxicity.Next,Quantum dots were used for high-level information security protection by combining their fluorescence properties with artificial intelligence.Because the printed pattern presents different information under visi ble light and ultraviolet light irradiation,and the neural network is almost impossible to crack,the scheme is highly deceptive,highly complex and unpredictable,so the information is well-protected.This method meets all the requirements of paper information protection,including good stability,low cost,easy preparation,and high security.