Piezoelectric Performance Of Semiconducting Organo-Metal Halide Perovskite/Mesoporous Polylactic Acid Based Composite Film Devices-Effect Of Ultrasonic Vibrations

Compositing is one common approach to introducing and advancing different properties of a functional material or device.Subsequently,there are various techniques of combining two or more materials to form a unified multifunctional/composite system.Whereas hybrid organo-metal halide perovskites?OMHPs?have been predominantly explored for photo or photo-enhanced applications,which are both time,location or light limited,they have shown multifunctionality when systematically blended with other materials.In this work,electrospinning,sol-gel and vertical ultrasonic assisted substrate vibration?UVPT?processes were employed to prepare and enhance the electroactivity of Poly lactic Acid?PLA?based/methylammonium lead triiodide?MAPbI₃?perovskite composite films.These were then used to fabricate small area mechano-electric/piezo-electric energy harvesters,on bendable substrates,via the following order.Firstly,semiconducting tin?iv?oxide electrospun nanofiber?SnO₂ NF?dispersions were prepared,appropriately mixed with polymer solutions of poly-L-lactic acid?PLLA?,polyvinylidene fluoride?PVDF?,and finally converted to thin mesoporous composite film structures via a systematic UVPT process.The resulting structures were studied and proved using field emission scanning electron microscopy?SEM?,Raman spectroscopy,Fourier transfer infrared spectroscopy?FTIR?,X-ray Diffraction?XRD?and electron dispersive spectroscopy?EDS?.Secondly,MAPbI₃ was then infiltrated into the porous composite scaffolds through vertical ultrasonic vibration of the substrates,followed by addition of other functional layers to complete the device construction.The introduction of MAPbI₃ and exposure to vertical ultrasonic vibrations altered the morphotropic phase nature of the composite towards more electroactive forms,without further electrical poling,the PVDF?and?phases individually rose by 80.61%and 32.44%respectively.There was an induced transformation of poly?L-lactic acid?from the?to the slacker?phase as deduced from XRD studies,a factor that seemingly enhanced the flexibility and thus mechanical endurance of the devices.Together with a review of related literature,experimental details and analysis of structures of the fundamental layers that made up the devices are captured in the first chapters of this thesis.The next chapter discusses the construction,characteristics,working mechanisms,and level of piezoelectric performance of fabricated devices,before a final summary and prospectus of thoughts for further research is presented.After device fabrication,a custom-made oscilloscope linked to a Keithley 6517 electrical source-meter was used to bend and read resulting mechano-electrical outputs of the devices.Furthermore,the mechano-electrical outputs of composited MAPbI₃ devices grown on other distinctive SnO₂ nanofiber and nanoparticle films,subjected to vertical ultrasonic vibrations were studied and compared to devices containing the PLA-PVDF-SnO₂ NF composite.The latter device showed superior performance in all cases when subjected to repeated compression-release cycles.The enhancement in performance of the composite device was attributed to the intrinsic piezo/ferroelectric potential of the polarizable polymer constituents,increased crystal order as a result of vertical ultrasonic vibration as well as the increased polarity along the film thickness?rendered by interfacial interactions between MAPbI₃,SnO₂ NF and the polar polymers?.Finally,the keithley source-meter obtained electrical measurements were employed to establish the effective piezoelectric strain coefficients/constants(d₃₃)of the different composite and non-composite films pursuant to the equation,q=d₃₃F.The effective d₃₃3 values obtained were gauged using a commercial piezometer.Generally,this dissertation is a report of the work starting from;the synthesis of a hybrid mesoporous polymeric framework,through;the deposition of a pure hybrid OMHP film on to these electret-like underlayers,the characterization and elucidation of the mechanisms involved,to a discussion of the maximum mechano-electrical conversion potential attained.This involved the use of both customised and standard equipment and methods.