ZnO-CuO core-shell heterostructure for improving the efficiency of ZnO-based dye-sensitized solar cells
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ZnO-CuO core-shell heterostructure for improving the efficiency of ZnO-based dyesensitized solar cells Kichang Jung1,3, Taehoon Lim2,3, Yaqiong Li3, Alfredo A. Martinez-Morales2,3 Department of Chemical and Environmental Engineering, University of California, Riverside, California 92507, U.S.A 2 Materials Science and Engineering Program, University of California, Riverside, California, 92507, U.S.A 3 Southern California Research Initiative for Solar Energy, University of California, Riverside, California 92507, U.S.A 1
ABSTRACT In this work, the integration of ZnO-CuO core-shell nanostructures shows improvement in the conversion efficiency of ZnO-based dye-sensitized solar cells (DSSCs). This is due to CuO acting as a secondary absorption layer that allows the absorption of nearinfrared (NIR) light increasing the generated photocurrent in the device, and as a blocking layer that reduces electron-hole recombination. The ZnO core and encapsulating CuO shell are synthesized through chemical vapor deposition (CVD), and thermal oxidation of a Cu seed layer, respectively. The crystallinity of the synthesized ZnO and CuO is analyzed by Xray diffraction (XRD). Scanning electron microscope (SEM) images show the change in morphology through the steps of Cu seed layer deposition and thermal oxidation of this layer. To determine optical properties of CuO on ZnO nanorods, UV-Vis-NIR photospectrocopy is used. The comparison of conversion efficiency of DSSCs using two different photoelectrodes (i.e. ZnO nanorods versus ZnO-CuO core-shell nanostructure) is performed by I-V measurements. INTRODUCTION Photovoltaic (PV) devices are a viable technology for helping meet future energy demands, by generating electricity from the sun—a clean, renewable, and endless source of energy [1,2]. Among the various type of the photovoltaic devices, organic-inorganic solar cells are one of the most promising technologies. Si-based solar cell panels are presently widely used due to their high efficiency, cost effectiveness, and durability. Nevertheless, new technologies such as organic-inorganic solar cells are necessary to achieve wider applications of PV devices such as in cellphones, automobiles, and wearable devices [3]. Traditionally, DSSC devices have used ruthenium-based dyes as a light absorption material. This dye can absorb ultraviolet and visible light (< 800 nm) and produce excited electrons from photon energy [4]. However, the main limitation arising from utilizing a ruthenium-based dye as an absorber is that it does not absorb infrared (IR) light (> 800nm), which accounts for 46% of sunlight [2]. This limitation of DSSCs restricts their conversion efficiency. Therefore, being able to utilize IR light has been identified as a major opportunity for improving the conversion efficiency of DSSCs [5]. Moreover, metal-oxide semiconductor materials are used as a photoelectrode in organic-inorganic solar cells. Especially for DSSCs, a semiconductor material is necessary for the transport of excited electrons from the dye to a transparent conduc
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