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Abstract: The decisive criterion associated with the species emission intensity ratio (Hα/SiH*) which characterizes the crystallinity of microcrystalline silicon (μc-Si) film was found to display an unstable behavior resulting from species concentration variation during μc-Si film growth with optical emission spectroscopy (OES) tool. In this study, a real-time process control system i.e. closed-loop system was developed. It aims to control the species intensity ratio with OES device in a very high frequency (VHF) plasma enhanced chemical vapor deposition reactor, via modulating the VHF power and silane dilution to improve μc-Si film growth for high efficiency a-Si/μc-Si tandem solar cell. The experiment results show that the closed-loop system stabilized the Hα/SiH* intensity ratio within a variation of 5% during the μc-Si film deposition process. Higher growth rate of μc-Si film with the same crystallinity was obtained in the closed loop system which consumed less power and SiH4 gas than in the open loop system, i.e. without process control. [Copyright &y& Elsevier]

Abstract: A PVdF-HFP/PEG/PEGDMA cross-linking film has been prepared as the electrolyte for dye-sensitized solar cell (DSSC). The film can be made porous by controlling the evaporation behavior of solvents. Room temperature ionic conductivity of the micro-porous film exceeds 1mS/cm. In addition, we also evaluated the significance of cell gap in DSSC by analyzing the impedance spectroscopy of the cell with polymer electrolyte. Finally, by decreasing the film thickness, the DSSC equipped with 11μm, micro-porous and cross-linked film showed a conversion efficiency over 4% and 5% under 1 and 0.16Sun, respectively. [Copyright &y& Elsevier]

A three-phase three-level rectifier with less power switches is proposed. Four power switches with voltage stress of half DC bus voltage are used in the circuit. A carrier-based current control strategy is proposed to draw the sinusoidal line currents with nearly unity power factor. The switching signals for power switches are derived from the DC bus voltage controller and neutral point voltage compensator. The mathematical model of the rectifier is derived and the control scheme is provided. To verify the proposed operation scheme, performance characteristics are given by experimental results. [ABSTRACT FROM AUTHOR]

An electron cyclotron resonance chemical vapor deposition (ECR-CVD) system applied in a hydrogenated amorphous silicon (a-Si:H) thin-film deposition process was diagnosed in-situ by using optical emission spectroscopy (OES) and a Langmuir probe. The optical actinometry technique was used to obtain the ratio of species concentration to the concentration of a trace gas (Ar). The electron temperature ( T e oes ) was estimated according to the spectrum intensity ratio of H β to Hα or that of Si* to SiH*, and the two estimation approaches were evaluated by comparing the results ( T e LP ) of Langmuir probe measurement. The probe surface contaminants (a-Si:H) produced during in-situ measurement created errors in the measurement of parameters such as the electron temperature and density ( N e ). The results indicated that, when a-Si:H was coated on the probe at thicknesses less than 150 nm, the errors were negligible. OES and Langmuir probe measurement were integrated and used to determine the dependence of the processing pressure and resonance magnetic field configuration on the properties of an a-Si:H film grown using ECR-CVD. When the process pressure was increased, the N e , T e oes and T e LP decreased; moreover, the Fourier-transform infrared spectroscopy results indicated that structure factor ( R* ) increased, and both the photosensitivity and hydrogen content ( C H ) decreased. An analysis conducted using OES and Langmuir probe measurement revealed, that the decreased concentration of the H radical reduced the passivation effect, and surface diffusion decreased. Furthermore, the gas partial pressure exerted a substantial influence on OES measurement. The volatility of the Ar spectrum intensity equaled the product of the volatility of N e and T e LP when the partial pressure effect is eliminated. Regarding the resonance magnetic field, the effects of plasma resonance position on film characteristics were substantial. The N e decreased greatly when the distance between quartz and the resonance zone was increased. [ABSTRACT FROM AUTHOR]