Effect Of Direct Current Bias Research Articles

Effect of direct current bias on MZO window layer in CdTe solar cells

The band alignment between magnesium-doped zinc oxide (MZO) and cadmium telluride (CdTe) is critical for enhancing the efficiency of CdTe solar cells. In order to study the effect of direct current (DC) bias on the MZO film, various DC biases were applied during the radio frequency (RF) sputtering of the MZO films, with the target bias ranging from 79 V to 121 V. The compositional, structural, chemical, and electronic properties of the MZO films were investigated. The optical transmission and x-ray photoelectron spectroscopy results show that the DC bias could modify the position of the Fermi level while having minimal impact on the band gap of the MZO film. The MZO films with different DC biases were employed as the window layer in CdTe solar cells. The device without DC bias exhibited a low efficiency of 7.7%, corresponding to a cliff-like conduction band offset near −0.1 eV. The optimal DC bias for the MZO film was found to be 99 V, leading to an improvement in efficiency to 12.9%, with a spike-like conduction band offset near 0.2 eV. Further increases in the conduction band offset, however, decrease the photo-generated current, negatively impacting device performance. The results emphasize the significance of DC bias in the RF sputtering process of MZO films with regard to the functionality of CdTe solar cells.

ELECTROMAGNETIC AND THERMAL CHARACTERISTICS SIMULATION FOR THREE-PHASE THREE-LIMB TRANSFORMERS UNDER DC MAGNETIC BIAS

Direct current (DC) bias is caused by DC intrusion into the transformer. DC bias will not only cause current distortion and damage electric power grid but also will lead to hot spot overheating and increase in the transformer insulation aging. The effect of DC bias on both electromagnetic and thermal characteristics of transformers should be simultaneously considered for transformer design and operation control. In this study, different levels of DC bias were introduced to a three-phase three-limb transformer. Magnetic flux offset and current distortion were obtained by field-circuit coupling simulation. The winding loss and hot spot for different loads were computed with the analytic method and the electromagnetic-thermal-fluid coupling model. The results indicate that the magnetic flux offset is sensitive to the variation of loads, but insensitive to the increase of DC. As the transformer is overloaded, the current distortion increases, and a peaked wave occurs. The harmonic frequencies of distorted current concentrate on even-order. Compared with the rated sinusoidal load, the hot spot temperature increased by 18.59 K with 10 A DC introduction. The hot spot location is transferred from the upper yoke of the core to the HV coil. As the load increases, the hot spot temperature increases first and then decreases. This study is of great significance to the assessment of DC bias effect.

Effects of direct current bias on nucleation density of superhard boron-rich boron carbide films made by microwave plasma chemical vapor deposition

We report bias enhanced nucleation and growth of boron-rich deposits through systematic study of the effect of a negative direct current substrate bias during microwave plasma chemical vapor deposition. The current flowing through a silicon substrate with an applied bias of −250 V was investigated for a feedgas containing fixed hydrogen (H2) flow rate but with varying argon (Ar) flow rates for 1330, 2670, and 4000 Pa chamber pressure. For 1330 and 2670 Pa, the bias current goes through a maximum with increasing Ar flow rate. This maximum current also corresponds to a peak in substrate temperature. However, at 4000 Pa, no maximum in bias current or substrate temperature is observed for the range of argon flow rates tested. Using these results, substrate bias pre-treatment experiments were performed at 1330 Pa in an Ar/H2 plasma, yielding the maximum bias current. Nucleation density of boron deposits were measured after subsequent exposure to B2H6 in H2 plasma and found to be a factor of 200 times higher than when no bias and no Ar was used. Experiments were repeated at 2670 and 4000 Pa (fixed bias voltage and Ar flow rate) in order to test the effect of chamber pressure on the nucleation density. Compared to 4000 Pa, we find nearly 7 times higher boron nucleation densities for both 1330 and 2670 Pa when the substrate was negatively biased in the Ar/H2 plasma. Results are explained by incorporating measurements of plasma optical emission and by use of heterogeneous nucleation theory. The optimal conditions at 1330 Pa for nucleation were used to grow boron-rich amorphous films with measured hardness as high as 58 GPa, well above the 40 GPa threshold for superhardness.

Effect of DC bias and RF self-bias on the structure and properties of chromium oxide coatings prepared by vacuum cathodic arc deposition

Cr2O3 coatings were prepared by vacuum cathodic arc deposition (VCAD) on cemented carbide YT15 at different voltages of both direct current (DC) and radio frequency (RF) bias. The structure and properties of the coatings were investigated by scanning electron microscope, X-ray diffraction, and nanoindentation. With both DC and RF bias, coatings deposited at zero and low bias voltage exhibit a columnar structure and a preferred orientation (PO) of (104). As the bias voltage increases, the columnar structure starts to disappear and PO gradually becomes (006). Besides, the crystallite size of the coatings declines as the bias voltage increases. Comparing to DC bias, the RF bias leads to smaller crystallite size by virtue of higher energy and density of ion bombardment. The electrical resistivity of the coatings and saturation ion current density during deposition were measured to explain this effect. The hardness of the coatings was significantly enhanced by the bias voltage, particularly by the RF bias. A nano-hardness of 44.7 GPa was found in the coating deposited under −100 V RF bias, which has not been previously reported.

DC Bias Simulation of 1000 kV UHV Transformer Based on MATLAB / Simulink

In order to study the effect of Direct Current bias on the excitation current of 1000kV UHV transformer caused by the parallel operation of DC transmission and AC transmission, this paper builds a simulation model of 1000kV three-winding autotransformer based on MATLAB/Simulink This paper introduces the simulation model of simulation model parameters, and builds a simulation model of 1000kV UHV AC transmission system. Based on the analysis of the change trend of excitation current when the DC voltage source is applied at the neutral point of the transformer, 1000kV transformer, the conclusion is that the DC bias suppression measures and the transmission line design work to provide a theoretical reference.

Direct current bias studies on (Bi 2O 3) 0.8(Er 2O 3) 0.2 electrolyte and Ag–(Bi 2O 3) 0.8(Er 2O 3) 0.2 cermet electrode

20 mol% erbia stabilized bismuth oxide (ESB) in the cubic fluorite structure is one of the highest oxygen ion conductors known. On annealing at temperatures below the transition temperature (∼600 °C), a fast continuous decay in oxygen ion conductivity occurs which has been attributed to the occupational and positional ordering on the oxygen ion sublattice. The reverse transition is characterized by the enthalpy required to disorder the ordered lattice. This study looked into the effect of direct current bias on the ordering kinetics of ESB solid electrolytes using symmetrical cells consisting of Ag–ESB cermet electrodes. Electrochemical impedance spectroscopy studies showed that on isothermal annealing at 500 °C, the current bias does not have a significant effect on the conductivity decay, though the differential scanning calorimetry (DSC) studies showed that under bias the endotherm related with the reverse transition appeared at shorter annealing time periods. Ag–ESB electrodes showed good performance, though were unstable at 625 °C under higher bias currents due to the Ag electromigration along with the oxygen flux.

The effect of direct current bias on the characteristics of Cu/C:H composite thin films on poly ethylene terephthalate film prepared by electron cyclotron resonance–metal organic chemical vapor deposition

Cu/C:H composite films were prepared on poly ethylene terephthalate (PET) substrate at room temperature by the electron cyclotron resonance–metal organic chemical vapor deposition (ECR-MOCVD) coupled with a negative direct current (DC) bias system. The negative DC bias voltage applied around the substrate strongly affected the crystallographic structure and composition as well as the surface roughness of the copper films. The surface resistivity of films decrease sharply as the bias voltage increase up to about 5 μΩ-cm below which the resistivity remains almost constant in the range of − 900 to − 1700 V. Thus, the bias voltage appeared to be a critical deposition parameter for preparing copper films with low resistivity. With interfacial studies of Cu-PET, copper atoms are embedded into the polymer substrate during the growth process. Therefore, Cu/C:H composite films on PET with good interfacial properties could be prepared by ECR-MOCVD coupled with a (−)DC bias system.

A Novel Phase Extraction for the Detection of Time Parameters in Signal

A unique technique to extract the phase in time domain is proposed in order to measure the time parameters such as speed and depth by transmitting sound and electric waves. In the signal analysis processing, the phase of pulse signal can be transformed and digitalized with local data in real time without the effect of direct current bias and Nyquist limits. This method is sensitive to base frequency of pulse signal with high spacial resolution and is effective to compare two signals which have different forms. It is expected that the phase analysis technique will be applied to the measurement of the speed and depth accurately by ultrasonic pulse signal in water.