ZnO nanowire (NW) grown on triple-junction (TJ) solar cells via the hydrothermal growth method to enhance efficiency is investigated. In this paper, experimental results indicate that TJ solar cells with ZnO NW as an antireflection (AR) coating have the lowest reflectance in the short wavelength spectrum, as compared with those of bare TJ solar cells (without AR coating) and solar cells with SiN x and TiO 2 /Al 2 O 3 AR coatings. ZnO NW has the lowest light reflection among all experimental samples, especially in the range of ultraviolet to green light (300-500 nm). It was found that ZnO NW could enhance the conversion efficiency by 6.92%, as compared with the conventional TJ solar cell. In contrast, SiN x and TiO 2 /Al 2 O 3 AR coatings could only enhance the conversion efficiency by 3.72% and 6.46% increase, respectively. The encapsulated results also suggested that the cell with ZnO NW coating could provide the best solar cell performances. Furthermore, all samples are measured at tilt angles of 0 -90 and results show that the solar cells with ZnO NW have the highest efficiency at all tilt angles. Furthermore, a small NW diameter increases light absorption.

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This study presents an optical switch that integrates an indium gallium zinc oxide (IGZO) thin-film transistor (TFT) and a GaInP/GaAs/Ge triple junction (TJ) photovoltaic (PV) cell. The device is driven by a TJ PV cell, which has a steady output voltage and a voltage regulator, to induce current in it. It should be noted TJ solar cell is broadband sensitive and the open circuit voltages are close under different illumination levels and a voltage regulator can assist it has identical working voltages. Moreover, The switch off (dark) and on (illuminated) current values of the optical switch are around 10 −8 and 10 −5 A, under different simulated test lights, respectively. The test light source is from solar simulator. The stable characteristics and good on/off ratio levels of this device under different light make it practicable in outdoor and indoor environments. Recently, self-powered devices that harvests power from the environment for sensing or electricity generation have attracted a lot of attention. Self-powered devices driven by solar, piezoelectric, thermal, acoustic energy and etc, have already been demonstrated. [1][2][3][4][5][6] In the published reports, Yang and his group fabricated self-powered devices by connecting an nanowire CdSe photodetector and a GaN/ZnO cell in series.7 Similar design optical driven transistor was also demonstrated. 8 However, those components in their design were easily effected by background light intensities.To solve the problem, authors introduced a vertical integration design and presented a self-powered optical switch device in this study. Similar study integrated a crystalline-Si interdigitated back contact (IBC) PV cell and a-IGZO TFTs with a direct 3D stacking structure. However, it connected several Si-based PV and cost dimensions.9 Compared with that, our device integrated an IGZO TFT and a GaInP/GaAs/Ge triple junction TJ PV cell into a chip which saved chip dimensions and got better performance, as shown in Fig. 1. For the TFT, IGZOwas chosen due to its high mobility, superior uniformity, and good transparency to visible light.10-15 A high-k material, Ta 2 O 5 , was used as the gate dielectric underneath IGZO film to control the conduction channel in IGZO. The TJ PV cell was adopted because it has the highest and stable output voltage among PV cells. Moreover, TJ solar cell is broadband sensitive and the open circuit voltages (Voc) are close under different illumination levels and a voltage regulator can assist it has identical working voltages (V m ). The test light source is from solar simulator. The stable characteristics and good on/off ratio levels of this device under different light make it practicable in outdoor and indoor environments.Which can produce higher current and on/off ratio to resist background light disturbances. 16 ExperimentalThe TJ PV cell comprises subcells of GaInP (top cell, bandgap energy Eg = 1.9 eV), GaAs (middle cell, Eg = 1.42 eV), and Ge (bottom cell, Eg = 0.67 eV). The structure is grown on Ge substrates using a metal-organic chem...

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