Controllable Synthesis And Device Assembly Of One-dimensional Semiconducting Oxides For Applications In Photodetectors

One-dimensional?1D?inorganic wide bandgap semiconducting oxides with tunable morphologies,high opto-electronic performance,flexible features,and rationally designed device assembly have exponentially growing demand for their practicable applications in optoelectronic devices.However,due to the complex synthesis techniques and lack of efficient assembling methods,the applications of 1D nanostructures are still limited.To meet these requirements,a cost effective and facile processing methodology is mandatory for their synthesis and integration into device assembly.In this regard,electrospinning is a scalable and cost-effective technique to synthesis ultrafine 1D nanostructures of diverse morphologies.With the optimization of system parameters and modifications in the processing,different types of 1D nanostructures nanofibers,nanobelts,and nanotubes can be prepared with high surface to volume and aspect ratios.Moreover,by designing the suitable collector,synthesized 1D nanostructures can be integrated into device assembly.In this dissertation,two types of high quality 1D nanostructures,nanofibers,and nanobelts were prepared by employing sol-gel assisted electrospinning method.Nanofibers of ZnO,In₂O₃,ZnGa₂O₄,WO₃,and ZnO-ZnGa₂O₄ and nanobelts of SnO_2,In/SnO₂,and In₂O₃-ZnO were synthesized.These nanofibers/nanobelts were collected uniaxialy aligned on self-designed modifier collector,and transferred to the different types of substrates for device assembly.Hybrid nanobelts based on In₂O₃ and ZnO were prepared.A facile,tunable,and cost effective method was employed to assemble the photodetectors by using well aligned electrospun nanobelts.These hybrid photodetectors have shown a high photoelectric performance as compared to their pure counterparts in terms of high photosensitivity,photodetectivity,high quantum efficiency,fast photoresponse,and at the same time extended spectral range?UV-vis?.Moreover,due to high aspect ratio of nanobelts,the photodetectors have shown high flexibility even at very small bending radii and after long bending cycles.The possible mechanism for the enhancement of these physical properties have also been discussed.We have also prepared free standing two-dimensional?2D?transparent and flexible nanobelts network that can be transferred to any type of flat or curved surface for the assembly of photodetectors.Tungsten oxide?WO₃?nanofibers were prepared and employed to assemble a dual band photodetector.The prepared photodetector has shown dual band photoresponse.Optical properties of the nanofibers were also investigated.Bandgap of the electrospun nanofibers was calculated on the basis of the absorbance spectrum.Their calculated band gap was found in good agreement with the theoretical value.In order to enhance the photoelectric performance of SnO₂,we prepared a series of In-doped SnO₂ nanobelts and analyzed effects of doping on the structural and photoelectrical properties.The photoelectric properties of the nanobelts were found in strong relation with indium doping concentration and the grain size of the nanobelts.It was analyzed that the doping compensation effects can enhance the photoelectric performance of the SnO2 nanobelts.Furthermore,highly flexible ZnO-ZnGa₂O₄ heterojunction nanofibers were prepared.We assembled photodetectors from high quality,well-oriented,uniaxially aligned hybrid ZnO-ZnGa2O4 nanofibers.The prepared photosensors have shown a large responsivity?1.73×10² A/W?,high Photodetectivity(1.02×10¹² Jones),and exceptional external quantum efficiency?7.10×10⁴%?along with fast rise and recovery time of less than 400and 500 ms,respectively,at a very low biasing voltage.In addition,the prepared photodetectors have shown outstanding flexibility and stability with more than 70%retention in the photosensitivity at a very small bending radius of 2 mm.It is also worth emphasizing that our assembled flexible photodetectors based on hybrid nanofibers,with high surface to volume ratio,have promising applications in the soft electronics and invisible optoelectronic devices.