Abstract
The thesis includes two parts: catalytic effect on InAs nanowire growth and polymer solar cell on large scale array nanobowl In doped tin oxide nanostructure for high performance electron devices. The influence of the catalyst materials on the electron transport behaviors of InAs nanowires (NWs) grown by a conventional vapor transport technique has been investigated. Utilizing the NW field-effect transistor (FET) device structure, ~20 % and ~80 % of Au-catalyzed InAs NWs exhibit strong and weak gate dependence characteristics, respectively. In contrast, ~98 % of Ni-catalyzed InAs NWs demonstrate an uniform n-type behavior with strong gate dependence, resulting in an average OFF current of ~10-10 A and a high ION/IOFF ratio of >104. The non-uniform device performance of Au-catalyzed NWs is mainly attributed to the non-stoichiometric composition of the NWs grown owing to different segregation behavior compared to that of Ni-catalyzed NWs, which is further supported with the in-situ transmission electron microscopy studies. These distinct electrical characteristics associated with different catalysts were further investigated by the first principle calculation. Moreover, top-gated and large-scale parallel-array FETs were fabricated with Ni-catalyzed NWs by contact printing and channel metallization techniques, which yield excellent electrical performance. The results shed light on the direct correlation of the device performance with the catalyst choice. A two-dimensional nanobowl array (2D-NBRs) with a unique honeycomb nanostructure was demonstrated with controllable VIII morphologies synthesized by the Langmuir–Blodgett (LB) method. The periodicity of 2D-NBRs can be controlled by utilizing different diameters of polystyrene (PS) balls ranged from 500 nm, 870 nm, 1 m to 2 m. The reflectance measurements revealed that the planar structure with a poly(3-hexylthiophene) (P3HT)/(6,6)-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction layer as an active layer exhibits a reflectance of ~20 %, while a significant reduction of the reflectance, 5– 7 % can be achieved after formation of 2D-NBRs at a PS ball diameter of 500 nm, which perfectly matches simulation results. From experimental results, the highest efficiency of 5.4 % with a filling factor of 66 % was achieved for the device with 2D-NBRs at PS ball diameter of 870 nm. Compared to a planar device with an efficiency of 3.9 %, a maximum enhancement of ~40 % can be achieved owing to the enhancement of Jsc because of unique honeycomb geometry, which exhibits a broadband and omnidirectional light harvesting behavior. Furthermore, a flexible solar cell was demonstrated with an enhanced efficiency of 30 % for a planar structure of 1 % to 1.3 % for 2D-NBRs structure.