Optical Switch of a-IGZO TFT and Triple Junction Photovoltaic Cell

Abstract

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...

Working process and opening characteristics of soft insulator of pulse motor

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