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This paper presents a highly efficient time-based maximum power point tracking (TB-MPPT) circuit with an enhanced three-dimensional tuning method. In the proposed circuit, firstly, the reconfigurable switched capacitor dc-dc converter with three conversion ratios is used to extend power range. The conversion ratio is selected according to input voltage level to avoid large charge redistribution loss. Secondly, the proposed algorithm can find the maximum power point with the minimum tuning switching frequency and capacitance control knob to reduce power loss, which results in high power conversion efficiency (PCE). The TB-MPPT circuit is fabricated with a 180nm CMOS process and has an active area of 0.42mm. The measured results achieve a peak PCE of 90.4%, a peak power tracking efficiency of 99.6%, and the output power of $52~\mu \text{W}$ in an energy harvesting system with four commercial PV cells.

This article proposes a highly efficient Time-Based Maximum-Power-Point-Tracking (TB-MPPT) integrated-circuit. Conventional TB-MPPT circuit shows unstable status (oscillation) near the Maximum Power Point (MPP), which causes the degradation of the overall power tracking efficiency. To overcome this critical issue, the proposed circuit separates the tracking operation into two periods, and it utilizes convergence range averaging technique with an adaptive perturbation step according to each control signal to accurately extract the current power level without oscillation problem. This work is fabricated in 180 nm CMOS process to demonstrate advantages of the proposed scheme. With 0.47V 12mW Photovoltaic (PV) cell, the measurement results show 94.2% of MPPT efficiency and 91.6% of power conversion efficiency (PCE). It occupies silicon chip area of 1.69 mm2.

Hollow nanosphere H-Gd2O3:Eu3+ was fabricated by multi-step chemical incorporated with hole soft mold using glucose. The H-Gd2O3:Eu3+ monodisperse nanosphere was obtained after thermal treatment at 650 °C. The structural, morphological, and luminescence optical properties of fabricated transparent samples were determined by X-ray diffraction, transmission and field-emission scanning electron microscopies, UV–Visible spectroscopy, Fourier transform infrared spectroscopy, photoluminescence spectroscopy, and Brunauer–Emmett–Teller method. The hollow nanospheres with diameter in the range of 80-100 nm, and the thickness of the shell is about 19 nm tightly packed by nanoparticles. The material is strongly luminescent in the red region, peak emissions correspond to transition characteristics such as 580 (5Do – 7Fo), 592 (5Do – 7F1), 611 (5Do – 7F2), 650 (5Do – 7F3), and 692 nm (5Do – 7F4). The luminescence efficiency was calculated based on the Judd–Ofelt theory, the luminescence efficiency of hollow nanosphere H-Gd2O3:Eu3+ is higher 1.56 than times Gd2O3:Eu3+ 48.45% which leads for many transparent optical devices. [ABSTRACT FROM AUTHOR]

Cu doped ZnS nanoparticles (ZnS:Cu) were synthesized by the co-precipitation method from Zn(CH3COO)2 0,1 M, Cu(CH3COO)2 0,1 M and Na2S 0,1 M solutions. Then they were coated by polyvinyl pyrrolidone (PVP) with different masses from 0.1 to 0.8 g. The photoluminescence excitation (PLE) spectra of 525 nm green photoluminescence (PL) band using xenon lamp shows the 330 nm peak and prominent peaks at 450, 470, 480 nm. The 330 nm peak is attributed by characterizes of nearshore absorption displacement of the ZnS crystal and the 450, 470, 480 nm peaks are involved in the adsorption displacement of Cu2+ (3d9) ions in the ZnS:Cu nanoparticles. The PVP coating hardly changes the crystal structure, the average crystal size, the morphology, the position of PL and PLE peaks that only increase their intensity. This enhancement is due to the transfer of excitation energy from PVP to Cu2+ ions (3d9) through the –C=O–M2+ (M2+: Zn2+, Cu2+) coordination bonds between the O atoms of the C=O group and ions Zn2+, Cu2+ on the surface of the nanoparticles. [ABSTRACT FROM AUTHOR]