| Summary: | 碩士 === 龍華科技大學 === 機械工程系碩士班 === 102 === Nanostructured zinc oxide has several practical applications as dye solar cells, sensors, nano LED, and flexible nanogenerator. In this project, low pressure chemical vapor deposition (LPCVD) was employed to make ZnO nano substances, for the application as electrode material of dye synthesized solar cells (DSSC).
Growth of ZnO was performed in a vertical, cold wall LPCVD system operated at 200 torr, a deposition temperature of 600oC, and using zinc acetylacetonate as precursor, nitrogen and oxygen as carrier gas. Mostly, copper nets, with average area of 1.0 cm2, were used as the substrate, to trigger the eutectic vapor-liquid-solid (VLS) growth of ZnO nanowires. After CVD, the deposit/substrate sets were immersed in N719 at room temperature. ITO glass served as the counter electrode. The ZnO electrode and the counter electrode were assembled and sealed. Potassium iodide solution was used as the electrolyte.
XRD patterns reveal that most deposits are polycrystal ZnO, with orientations at (100), (002), (101), (102), and (110). SEM images show that these nano wires have a length from 3 to 7 μm, and a diameter from 60 to 500 nm. It has been recognized that, doping of iron acetylaetonate in CVD precursor is helpful for formation of ZnO nanowires. If zinc oxide buffer layer was used as CVD substrate, SEM observes granular ZnO deposits, while XRD identifies a strong (002) prefential orientation. But elecgtrical current voltage measurement points out that DSSC uses CVD ZnO/ZnO buffer is inferior to DSSC uses CVD ZnO/Cu.
Generally, using a transitional metal, such as copper, as substrate, and mix zinc CVD precursosr with iron acetylacertonate around 10 wt %, are the process window to produce better electrodes. DSSC use such electrode can yield a short-current density of 0.23 mA/cm2 and the open-circuit voltage of 0.74 V.
A simple conceptual model was proposed to describe the role of iron acetylacertonate in LPCVD ZnO. It seems that, the amount of Fe(acac)3 being added will influence the nucleus size, density, plus diameter and distribution density of ZnO nanowires. In certain circumstances, the amount of Fe(acac)3 may also manipulate the axial and radial growth rates of ZnO pillars.
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