Papers by Keyword: LBIC

Abstract: This work presents recent advances in the characterisation of carrier recombination and impurities at Fraunhofer ISE. The role of iron contamination during crystallisation is analysed in more detail. Numerical simulations and comparisons to experimental data are presented which demonstrate the impact of iron from the crucible and crucible coating and show the in-diffusion of iron into the silicon melt as well as into the solid silicon during crystal cooling. Measurements of spatially resolved carrier lifetime and interstitial iron concentration on wafers after phosphorus diffusion gettering are used as input for cell efficiency modelling which reveals the specific and quantitative role of iron on cell parameters in multicrystalline silicon. A new photoluminescence based method is presented which quantitatively determines the interstitial iron concentration in finished solar cells. We finally present advances in defect characterisation with sub-micrometre resolution: We show recent progress in micro photoluminescence spectroscopy for the quantitative measurement of interstitial chromium with high spatial resolution. A further development of this setup will be discussed: By combining the principle of Light Beam Induced Current (LBIC) or voltage (LBIV) and the highly localized illumination, images of carrier recombination at local defects are presented which feature a, compared to EBIC, higher signal-to-noise ratio.

Abstract: A comparative study of multicrystalline Si based solar cells and plastically deformed single crystalline Si by the EBIC, LBIC and XBIC methods as well as a computer simulation were carried out. The XBIC measurements were realized on a laboratory X-ray source. Simulations of LBIC and XBIC contrast values for grain boundaries, dislocations and spherical precipitates were carried out for different diffusion length and beam diameter values. It is shown by a computer simulation that the LBIC and XBIC contrast of two-dimensional defects in the crystals with a large enough diffusion length can be a few times higher than that in the EBIC mode, i.e. these methods in recent multicrystalline Si structures allow to reveal grain boundaries with the lower recombination strength. The contrast of dislocations perpendicular to the surface can be comparable in all three methods. The XBIC and LBIC contrast of precipitates usually is essentially smaller than that in the EBIC mode and could approach it in the structures with the small diffusion length only. Experimental data confirming the results of simulations are presented.

Abstract: In this paper we combine LBIC and EL measurements of commercially multi-crystalline silicon solar cells, in order to obtain detailed information about the electrical activity around defect areas. This integrated analysis is suitable for the study of different crystal defects at both micrometric and full wafer scale. In particular, the electrical activity of some defect areas is studied in detail by means of highly spatially-resolved LBIC maps, showing important differences in their behaviours. A discussion about the origin of these differences is presented.

Abstract: For the development of concentrator photovoltaic (CPV) module realizing high efficiency, it is necessary to achieve the high efficiency optical system including Fresnel lens and homogenizer. For the improvement of optical systems, it is very important to understand the contribution of the light irradiated to a localized position on the Fresnel lens. The light beam induced current (LBIC) system was constructed to evaluate the focusing characteristic of the CPV module. We locally irradiated a light from solar simulator to the CPV mini-module and measured the generation current, and the localized characteristics were represented by two-dimensional mappings. Moreover, we evaluated the influence of tracking error by changing the irradiation angle. In the case of tracking errors, the peak of generated current was shifted and the current was decreased. In the case of tracking error of 1.0 o, the total generated current was reduced 12%, in comparison with the normal irradiance.

Abstract: We report on a light-beam-induced current (LBIC)-analysis of metal silicide defects arising from co-precipitation of copper and nickel in Cz-silicon-bicrystals produced by wafer direct bonding. Large colonies of silicide precipitates in the one wafer emerging from undisturbed growth from few nucleation sites were observed in different orientations with respect to the surface which correspond to Si {110} planes. From this, the colonies formed during copper-nickel co-precipitation reveal the same attributes as those colonies typical for copper precipitation in the absence of nickel. Oxygen related defects associated with a higher defect distribution in the other wafer were characterized by means of high resolution Transmission Electron Microscopy (TEM) and their temperature dependent LBIC signal.

Abstract: The paper describes the elaboration of a method for producing composite Si/SiC wafers and investigation of their properties. The known two-shaping elements (TSE) method was used to produce the material. Pilot tests show that this composite material can be used for production of solar cells. The structure of silicon grains is elongated relative to the growth direction, the dislocation density in grains is of about (5÷8) ×104 cm-2, the average lifetime of minority carriers is 4÷6 µs.