Circuit prevents overcharging of secondary cell batteries

Circuit prevents battery cell overcharging by detecting and reducing the charging voltage to the open-circuit voltage of the battery when this current falls to a predetermined value. The voltage control depends on the fact that the charging current falls significantly when the battery nears its fully charged state

Electrical performance study of a large area multicrystalline silicon solar cell using a current shunt and a micropotentiometer

In this paper, a new technique using a Current Shunt and a Micropotentiometer has been used to study the electrical performance of a large area multicrystalline silicon solar cell at outdoor conditions. The electrical performance is mainly described by measuring both cell short circuit current and open circuit voltage. The measurements of this cell by using multimeters suffer from some problems because the cell has high current intensity with low output voltage. So, the solar cell short circuit current values are obtained by measuring the voltage developed across a known resistance Current Shunt. Samples of the obtained current values are accurately calibrated by using a Micropotentiometer (μpot) thermal element (TE) to validate this new measuring technique. Moreover, the solar cell open circuit voltage has been measured. Besides, the cell output power has been calculated and can be correlated with the measured incident radiation

Recombination in polymer-fullerene bulk heterojunction solar cells

Recombination of photogenerated charge carriers in polymer bulk heterojunction (BHJ) solar cells reduces the short circuit current (Jsc) and the fill factor (FF). Identifying the mechanism of recombination is, therefore, fundamentally important for increasing the power conversion efficiency. Light intensity and temperature dependent current-voltage measurements on polymer BHJ cells made from a variety of different semiconducting polymers and fullerenes show that the recombination kinetics are voltage dependent and evolve from first order recombination at short circuit to bimolecular recombination at open circuit as a result of increasing the voltage-dependent charge carrier density in the cell. The "missing 0.3V" inferred from comparison of the band gaps of the bulk heterojunction materials and the measured open circuit voltage at room temperature results from the temperature dependence of the quasi-Fermi-levels in the polymer and fullerene domains - a conclusion based upon the fundamental statistics of Fermions.Comment: Accepted for publication in Physical Review B. http://prb.aps.org/accepted/B/6b07cO3aHe71bd1b149e1425e58bf2868cda2384d?ajax=1&height=500&width=50

Effects of high doping levels silicon solar cell performance

The significance of the heavy doping effects (HDE) on the open-circuit voltage of silicon solar cells is assessed. Voltage calculations based on diffusion theory are modified to include the first order features of the HDE. Comparisions of the open-circuit voltage measured for cells of various base resistivities are made with those calculated using the diffusion model with and without the HDE. Results indicate that the observed variation of voltage with base resistivity is predicted by these effects. A maximum efficiency of 19% (AM0) and a voltage of 0.7 volts are calculated for 0.1 omega-cm cells assuming an optimum diffused layer impurity profile

Suppression of Edge Recombination in InAs/InGaAs DWELL Solar Cells

The InAs/InGaAs DWELL solar cell grown by MBE is a standard pin diode structure with six layers of InAs QDs embedded in InGaAs quantum wells placed within a 200-nm intrinsic GaAs region. The GaAs control wafer consists of the same pin configuration but without the DWELL structure. The typical DWELL solar cell exhibits higher short current density while maintaining nearly the same open-circuit voltage for different scales, and the advantage of higher short current density is more obvious in the smaller cells. In contrast, the smaller size cells, which have a higher perimeter to area ratio, make edge recombination current dominant in the GaAs control cells, and thus their open circuit voltage and efficiency severely degrade. The open-circuit voltage and efficiency under AM1.5G of the GaAs control cell decrease from 0.914V and 8.85% to 0.834V and 7.41%, respectively, as the size shrinks from 5*5mm2 to 2*2mm2, compared to the increase from 0.665V and 7.04% to 0.675V and 8.17%, respectively, in the DWELL solar cells

Multiple State Representation Scheme for Organic Bulk Heterojunction Solar Cells: A Novel Analysis Perspective

The physics of organic bulk heterojunction solar cells is studied within a six state model, which is used to analyze the factors that affect current-voltage characteristics, power-voltage properties and efficiency, and their dependence on nonradiative losses, reorganization of the nuclear environment, and environmental polarization. Both environmental reorganization and polarity is explicitly taken into account by incorporating Marcus heterogeneous and homogeneous electron transfer rates. The environmental polarity is found to have a nonnegligible influence both on the stationary current and on the overall solar cell performance. For our organic bulk heterojunction solar cell operating under steady-state open circuit condition, we also find that the open circuit voltage logarithmically decreases with increasing nonradiative electron-hole recombination processes.Comment: 6 pages, 4 figure

Further study of inversion layer MOS solar cells

A group of inversion layer MOS solar cells has been fabricated. The highest value of open-circuit voltage obtained for the cells is 0.568V. One of the cells has produced a short-circuit current of 79.6 mA and an open-circuit voltage of 0.54V. It is estimated that the actual area AMO efficiency of this cell is 6.6 percent with an assumed value of 0.75 for its fill factor. Efforts made for fabricating an IL/MOS cell with reasonable efficiencies are reported. Future work for 4 sq cm IL cells and 25 sq cm IL cells is discussed

Comparison of 'shallow' and 'deep' junction architectures for MBE-grown InAs/GaAs quantum dot solar cells

We report on the fabrication of InAs/GaAs quantum dot solar cells with high open circuit voltage by molecular beam epitaxy. `Shallow' and `deep' junction architectures were compared. The highest open circuit voltage of 0.94 V was obtained for the `shallow' junction configuration. The open circuit voltage of InAs quantum dot solar cells decreased only by ~40 mV compared to GaAs reference cells for both junction architectures indicating high quality quantum dots. The open circuit voltage of InAs/GaAs quantum dot solar cells was also found to be dependent on the size of quantum dots

A maximum power point tracking for a photovoltaic system based on optimum sinusoidal modulated control pulses

Photovoltaic systems have grown rapidly in the last few decades. This growth has enhanced research about this technology, focusing on reducing cost and improving efficiency. Maximum power point tracking (MPPT), which increases the overall efficiency of a PV system, is a main part of a PV system. In this paper, some MPPT methods have been critically reviewed. Fractional open-circuit voltage has been investigated. The approach of a separate PV array to obtain the open circuit voltage (Voc) is adopted. The proposed idea in this paper is based on optimising the control pulses for the DC-DC converter. The generation of control pulses is based on sinusoidal modulated pulse width modulation (SPWM). The output from the DC-DC converter is then fed into a low frequency square wave voltage-fed inverter circuit. The output is a fine sinusoidal waveform, although the inverter operates at a low frequency. The block diagrams and the results are presented