Development of Organic and Inorganic Nanostructured Thin Films through Electrohydrodynamic Atomization towards Multifunctional Applications

Abstract

This chapter summarizes the entire results and over all achievements in this thesis. Concluding, this dissertation presented the basic understanding of electrohydrodynamic atomization technique and deposition of nanostructured functional thin films with detailed spectroscopic characterizations. Our experimental results suggesting that the deposition of functional thin films can be controlled by the physico-chemical properties of precursor solution or ink and the atomization process of EHDA. On this basis, we have presented different types of functional thin films (organic, inorganic and composites) for wide range of multifunctional applications. Initially, we have discussed the merits and demerits of conventional techniques for thin film deposition and then motivation and importance of alternative technique of electrohydrodynamic atomization for large scale thin film deposition on different substrates (flexible and non-flexible). This chapter clearly discussed the working principle, importance of atomization modes such as dripping, micro-dripping, unstable cone-jet, stable-jet and multi-jet and also significant influence of process parameters (flow rate, applied potential, stand-off distance, etc.) along with physico-chemical properties of precursor solution or ink. With the understanding the basic principle of EHDA, We used to deposition of functional organic thin films such as PEDOT:PSS and multi-layered thin films. The PEDOT:PSS thin film deposited on flexible PET substrate. Optimum flow rate and applied potential for stable cone jet mode has been confirmed through operating envelope. The uniformity and film thickness has been investigated by a field emission scanning electron microscope. The thin film shows nearly 75-82 % transmittance in visible region. The electrical study shows good ohmic behavior of PEDOT:PSS thin film with the resistivity of approximately 49.6 mΩ cm. However, multi-layered P3HT:PCBM/ PEDOT:PSS deposited on ITO coated flexible substrate. Deposition conditions such as stable cone jet formation, flow rate and applied potential have been investigated. X-ray diffraction analysis revealed the presence of P3HT polymer in the as deposited film. Surface morphology of the films are investigated using a field emission-scanning electron microscope confirms that a uniform deposition of thin films was achieved. The current?voltage characteristics of the as deposited films show a rectifying behavior. The capacitance?voltage study indicated that the frequency dependent capacitance of the as deposited thin films depended on the frequency. We also demonstratedthat the deposition of nanostructured metal oxide thin films using EHDA process. Herein, the deposition of nanostructured TiO2 ZnO and NiO thin films using the EHDA technique with organic polymers as a stabilizer. The required parameters for achieving the uniform films using EHDA are also discussed in detail. X-ray diffraction results confirmed that the TiO2 ZnO and NiO films were oriented in the anatase, wurtzite and cubic phases. Field emission scanning electron microscope studies revealed the uniform deposition of the nanostructured metal oxides thin films. The purity of the films are characterized using Fourier transform infra-red (FTIR) and X-ray photoelectron (XPS) spectroscopy confirming the presence of Ti?O, Zn?O and Ni?O bonding in the films without any organic residues. The optical properties of the thin films were measured by the UV-visible spectroscopy which shows the transparency of the films is in the visible region. The current-voltage (I-V) curve of the TiO2 thin films shows a nearly linear behavior with 45 mΩ.cm of electrical resistivity. The photocurrent measurement of ZnO thin film is investigated under the UV light illumination. Finally, the electrochemical analysis of NiO thin film demonstrated that the electrode behavior and storage capacity for energy storage application. Finally, Silver nanowires (AgNWs) embedded PEDOT:PSS nanocomposite thin films was deposited on flexible substrate through EHDA. The optimization of flow rate and applied potential for achieving uniform thin film via Taylor cone formation has been discussed in detail. The crystallinity and surface morphology of the as-deposited thin films was investigated by X-ray diffraction and field emission scanning electron microscope. The X-ray photoelectron spectroscopy results showed that the nature of chemical bonding and film purity of intercalated AgNWs in PEDOT:PSS matrix. The optical and electrical studies revealed high transparency in the visible region and lower sheet resistance of the AgNWs/PEDOT:PSSthin films. These results indicate that the AgNWs embedded PEDOT:PSS is a key factor to enhance the film conductivity without any loss of optical properties which may create new horizon in their potential applications in optoelectronics. The unique advantage of EHDA technique play a significant role for the manufacture of functional thin films based printed devices at room atmospheric conditions and this thesis is used to further illuminates the EHDA process as an alternative to conventional techniques.