V. Schlosser

Kelvin probe measurements of microcrystalline silicon on a nanometer scale using SFM

Work function measurements on cross-sectioned microcrystalline pin silicon solar cells deposited by Hot-Wire CVD are presented. The experiment is realized by combining a modified Kelvin probe experiment and a scanning force microscope. The measured surface potential revealed that the built-in electric drift field is weak in the middle of the compensated intrinsic layer. A graded donor distribution and a constant boron compensation have to be assumed within the intrinsic layer in order to obtain coincidence of the measurements and simulations. The microcrystalline p-silicon layer and the n-type transparent conducting oxide form a reverse polarized diode in series with the pin diode.

Limiting factors for the application of crystalline upgraded metallurgical grade silicon

Differently processed upgraded metallurgical grade silicon (UMG-Si) has been used to produce planar diffused solar cells. The results obtained from these cells were used to evaluate the limiting factors governing the conversion efficiency in UMG-Si-cells. The present state of practical cell processing was taken into account for the discussion of the potential of new technologies. For conventionally processed cells on UMG-Si having a planar junction, it appears that a conversion efficiency of about 13 percent under AM1.5 conditions (incident light intensity = 1 kWm-2, T= 27°C) cannot be exceeded. Experimentally a conversion efficiency of 10.5 percent was obtained.

Superconducting fluctuations in YBaCuO thin films

Abstract Measurements of the electrical conductivity, the magnetoconductivity and the Hall effect on thin films of YBaCuO in the regime of thermodynamic fluctuations of the superconducting order parameter are reported. The fluctuation conductivity is in good agreement with the 2-dimensional Aslamazov-Larkin theory. Excess magnetoconductivity and excess Hall effect diverge by higher exponents near the critical temperature indicating a pronounced effect of the magnetic field on the fluctuations.

A systematic optical study of the Ba1−xKxBiO3 system

Reflection spectra of Ba1−xKxBiO3 over a wide spectral range are reported. For x lower than the critical value of ∼ 0.35 contributions of free carriers, interband transitions and midgap absorption processes are observed. The plasma frequency is small (< 0.1 eV) for all x below the insulator to metal transition. Increasing x from 0 to ∼ 0.1 results in a transfer of oscillator strength from the interband maximum to a midgap maximum. For x = 0.3 a flat plasma edge is observed, which is deformed by remainders of both the interband and midgap maxima.

Diagnostics and testing of photovoltaic devices

The aim of this paper is the investigation of electrical and acoustic properties of solar cells assembled into modules, before and after forced and accelerated ageing. It has been shown that impedance spectroscopy measurement and characterization is an important tool to reveal the degradation changes due to high voltage stress and environmental stress. The parameters of photovoltaic (PV) cells and modules have been derived from electric and acoustic measurements. Important differences between the results of measurements have been found before and after the PV cells and modules underwent the stressing.

An acoustic set up for the vibration analysis of silicon wafers

Two simple experimental set-ups for acoustic mode analysis of silicon wafers were established. Audible vibratory mode data of single- and multi-crystalline silicon wafers with different thicknesses were investigated. Natural frequency data were found to correlate linearly with the wafer thickness. The observed dependence is theoretically explained by the Kirchhoff plate model. Deviations from the linear variation are attributed to inhomogeneities and mechanical damage of the wafer. Mechanical defects are the reason for an increased fracture probability.

About the usability of a photovoltaic module to monitor air pollution

The responsivity by means of the quotient of photo-current and incident global light intensity of a solar module situated in central Vienna was analyzed during a period where an ash cloud of volcanic origin was spread over central Europe in spring 2010. A timely coincidence between anomalies of the registered responsivity and the concentration of ash particles in the air was found. However due to the lack of reliable directly observed particle concentration no correlation could be established.

A study of vibration induced distortion on the performance of photovoltaic converters

Mechanical vibrations of a solar module cause oscillations in the orientation of the module towards the sun, resulting in a low frequency a.c. current component at the modules terminals. We have investigated this effect and performed model calculations in order to estimate the influence on the feed back control of a converter.

Electrical and micromechanical performance of ultrasonically cleaned silicon wafers

The evolution of the electrical and micromechanical properties of Si wafers subjected to a kHz-frequency ultrasonic treatment in a water-containing ultrasonic cleaning bath is reported. The cleaning stages observed with varying treatment time are discussed. It is believed that, wafer treating during the first ≈ 60 min is capable of removing contaminating particulates from the wafer surface and actives interface dangling bonds. These are leading to a decrease of subsurface resistance towards dislocation displacements as observed by the micro-hardness decrease, affect free carrier migration barriers seen in variations of the I-V barrier heights, and acts as recombination centers resulting in accelerated photovoltage decays. Although an exact mechanism is not yet clarified, a partial healing of the bonds may occur at longer cxcitation times (≈ 60–120 min) thus partially reversing the observed changes.

Imaging the transmission of light through a crystalline silicon wafer with a silicon detector array

A simple experimental set up for capturing the distribution of light transmitted through a silicon wafer is presented. As sensing element a silicon based charge coupled device, CCD of a 4 Megapixel camera was used. The responsitivity of the camera in the optical NIR wavelength range was evaluated. The applicability of a pulsed Xenon arc lamp built into a photographers flash light as light source was investigated. First results from transmission images proof the potential of these two components for further applications in the solar industry.