| Summary: | 碩士 === 國立交通大學 === 電子工程系所 === 94 === In this work, we used CdSe/ZnS (core/shell) and/or Au NPs to construct the multi-layered photo-sensing nanodevice structures on a silicon substrate through ionic interaction. ZnS with larger energy bandgap served as a passivation layer on CdSe NPs to enhance the stability and quantum yield. From the results of UV-visible absorbance and photoluminescence spectra, CdSe/ZnS NPs
exhibit better optical properties than CdSe NPs in the previous work.
For the four-layered nanostructure composed of CdSe/ZnS and Au NPs, there was constantly about 28 nA (30μm / 5μm) and 70 nA (30μm / 15μm) increment to the current measured in the dark for each voltage bias after illumination with 375 nm laser. In addition to 375 nm, 400 nm and 435 nm lasers were also used as light sources for photo-excitation. We found that more photocurrent was generated under shorter wavelength illumination, which was also verified in the absorption / emission spectra. Besides, more photocurrent was generated in the nanostructure with a longer length or a larger number of layers, which can be successfully explained by using the model of “nano-Schottky-diodes and resistor array”. We can obtain the same phenomenon as using HSPICE to simulate the two dimensional model. Finally, we found that the“photocurrent volume density (PVD)”of the 4-layered Au / AET-CdSe/ZnS nanostructure is at least 1183 times better than that of CdSe thin film structure. The power conversion efficiency can achieve 40% based on ourideal inference.
In addition to nanodevice composed Au and CdSe/ZnS NPs, we constructed multi-layered structure on the silicon oxide substrate by using only CdSe/ZnS NPs. MSA-CdSe/ZnS and AET-CdSe/ZnS NPs, which were chemically modified prior to ionic assembly process, have negative-charged and positive-charged functional groups on the surface of the NPs respectively. We found that the PVD of the 12-layered structure is at least 34 times better than that of conventional CdSe thin film structure. Finally, we conclude that the Au / AET-CdSe/ZnS nanodevice acts like a photodiode while the MSA-CdSe/ZnS / AET-CdSe/ZnS nanodevice acts like a typical traditional photoresistor. Besides, the Au / AET-CdSe/ZnS nanodevice has enormous potential to turn into solarcells applications.
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