Electrodeposition of Electroluminescent CdSe Nanowire Devices
Electrodeposited nano-materials have huge potential to reduce the cost of nano and micro fabrications dramatically especially in light emitting diodes field. It is difficult to fabricate high performance devices and understand the working mechanisms due to the polycrystalline nature of most electrodeposited materials. In this dissertation, electrodeposited cadmium selenide was used to fabricated two different structures of light emitting devices. In the second chapter, the preparation by electrodeposition of transverse nanowire electroluminescent junctions (tn-ELJs) is described and the electroluminescence (EL) properties of these devices are characterized.The resulting linear array of nickel-CdSe-gold junctions produce electroluminescence (EL) with an external quantum efficiency, EQE, and threshold voltage, Vth, that depends sensitively on wCdSe. EQE increases with increasing electric field and also with increasing wCdSe, and Vth also increases with wCdSe, and therefore the electrical resistance, of the tn-ELJs. Vth down to 1.8(±0.2)V (for wCdSe ≈ 100 nm) and EL of 5.5(±0.5) 10^-5 (for wCdSe ≈ 450 nm) are obtained. tn-ELJs produce a broad EL emission envelope, spanning the wavelength range from 600 - 960 nm. In the third chapter, A wet chemical process involving two electrodeposition steps followed by a solution casting step, the EESC process, is described for the fabrication of electroluminescent, radial junction wires. EESC is demonstrated by assembling three well-studied nanocrystalline (or amorphous) materials: Au,CdSe, and PEDOT:PSS. The tri-layered device architecture produced by EESC minimizes the in influence of an electrically resistive CdSe emitter layer by using a highly conductive gold nanowire that serves both as a current collector and a negative electrode. Hole injection, at a high barrier CdSe-PEDOT:PSS interface (Φh ≈ 1.1 V), is facilitated by a contact area that is 1.9 - 4.7 fold larger than the complimentary gold-CdSe electron-injecting contact (Φe ≈ 0.6 V) contributing to low voltage thresholds (1.4 - 1.7 V) for EL emission. Au@CdSe@PEDOT:PSS wire EL emitters are 25 μm in length, but the EESC process is scalable to nanowires of any length, limited only by the length of the central gold nanowire that serves as a template for the fabrication process. Radial carrier transport within these multishell wires conforms to the back-to-back diode model.