(CdSe) ZnS core shell quantum dots decorated zinc oxide nanowires for solar energy harvesting applications
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(CdSe) ZnS core shell quantum dots decorated zinc oxide nanowires for solar energy harvesting applications Abhishek Prasad1, Archana Pandey1, Karl Walczak2, Craig Friedrich2 and Yoke Khin Yap1 1 Department of Physics 2 Department of Mechanical Engineering-Engineering Mechanics Michigan Technological University Houghton, Michigan 49931, U.S.A. ABSTRACT ZnO nanostructures have proven to be versatile functional materials with promising electronic, piezoelectric and optical properties. Here, we report on the application of (CdSe) ZnS Core Shell quantum dots decorated ZnO Nanowires (ZnONWs) and Nanobelts (NBs) in solar energy harvesting. Results indicate that both as grown and decorated ZnO Nanostructures are photoactive, have a fast response time and generate photocurrent under excitation in a photoelectrochemical cell setup. An order of magnitude enhancement in the photocurrent response of (CdSe) ZnS Core Shell quantum dots decorated ZnONBs is seen as compared to response from as grown ZnONBs. Generated photocurrent decreases with time but stabilizes at higher value for (CdSe) ZnS Core Shell quantum dots coated ZnONBs. Detailed performances of these devices are discussed.
INTRODUCTION To meet our ever increasing energy demand, it is necessary to utilize solar energy in an efficient and cost effective manner. Hence, design of more efficient materials and better device architecture for photocurrent generation is being widely investigated. ZnO, due to its direct bandgap, and the anisotropic crystal structure that can be grown in various forms of nanostructures, is an ideal candidate for various nanoscale devices. ZnO nanostructures are being hotly pursued for piezoelectric [1], nanoelectronic [2], solar cell [3] and various other [4] energy harvesting applications. On the other hand, semiconductor nanocrystals known as Quantum Dots (QDs) are being used to enhance the light harvesting capabilities of existing solar cell device architectures [5]. To enhance the photoconversion efficiency, ZnO nanostructures have been sensitized with various types of QDs including CdSe QDs [6], CdTe QDs [7] , CdS QDs [8], (CuInS2) ZnS core shell QDs [9]. CdSe and CdS QDs co-sensitized ZnONW arrays have also been reported for hydrogen generation [10]. Although various QDs have been used but large increase in efficiency and performance is not observed. This can be due to several reasons. First is lack understanding of the surface chemistry between nanowires and QDs. Second is the stability of QDs in the electrolyte medium is not clear. Since core shell QDs have been explored for increasing the stability of QDs [11,12], here we compare the photocurrent output from (CdSe) ZnS core shell QDs decorated ZnO NWs and NBs. EXPERIMENT A conventional thermal chemical vapor deposition (CVD) technique was used for the synthesis of ZnO NWs and NBs. Indium tin oxide (ITO) coated glass substrates (Delta
Technologies) were used as the substrates for the growth of these ZnO nanostructures. ZnO and graphite powders in a weight ratio of 2:1 were inserted to t
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