M. Werner

Oxygen and Carbon Precipitation in Multicrystalline Solar Silicon

Oxygen and carbon are the main impurities in multicrystalline silicon for photovoltaic applications. Precipitation of oxygen and carbon occurs during crystal growth and solar cell processing. Depending on the thermal conditions and the initial oxygen and carbon content various types of SiO2, SiC precipitates and oxygen related defects are observed and investigated by IR spectroscopy and transmission electron microscopy. Topographic μ-PCD measurements are used to study the minority carrier lifetime in the material locally. It is found that certain types of oxygen defects reduce the lifetime of the bulk and enhance the recombination activity of dislocations. Quantitative measurements of the oxygen precipitation of pre-annealed specimens are carried out to study the oxygen precipitation systematically. A statistical nucleation and growth model using rate equations and a Focker-Planck equation is applied to simulate the precipitation process numerically.

Nanometer-scale metal precipitates in multicrystalline silicon solar cells

In this study, we have utilized characterization methods to identify the nature of metal impurityprecipitates in low performance regions of multicrystalline silicon solar cells. Specifically, we ha ...

Measurement of the Normalized Recombination Strength of Dislocations in Multicrystalline Silicon Solar Cells

An improved technique is presented to measure the normalized recombination strength Gat dislocations in silicon solar cells that were fabricated of cast grown silicon. G is the number ofrecombinations per unit time, length, and excess carrier density divided by the minority carrierdiffusion coefficient D. The measurement is based on fitting the theoretical correlation betweeninternal quantum efficiency IQE at a single wavelength and dislocation density r to the measureddata. The IQE is measured topographically by the light beam induced current (LBIC) method. Foreach point of the LBIC map a dislocation density is determined by analysing the etched samplesurface with an image recognition programme. The theory for IQE(r) combines Donolatosprediction for L(r) with a calculation of IQE(L) made by the computer programme PC1D. L is thediffusion length of the minority carriers. The programme PC1D takes special properties of the solarcell process into account. The method was applied to solar cells made by a conventional furnaceprocess as well as a rapid thermal process (RTP). In the latter case a correlation between G and theemitter diffusion temperature was found. Finally TEM measurements were made to investigatedislocations with different values of G.

Oxygen and lattice distortions in multicrystalline silicon

Abstract Oxygen is one of the main impurities in multicrystalline silicon for photovoltaic applications. Precipitation of oxygen occurs during crystal growth and solar cell processing. It is shown that dislocations enhance the oxygen precipitation. Depending on the thermal conditions and the initial oxygen content various types of SiO 2 +precipitates and oxygen related defects are observed and investigated by fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy. The large area distribution of oxygen decorated dislocations is studied by scanning infrared microscopy (SIRM). Both inhomogeneous distributions of dislocations and oxygen precipitates occur and can lead to internal stresses. The internal stresses of multicrystalline-silicon wafers are investigated by an optical method using polarized infrared light. The results are compared with the dislocation microstructure and the oxygen distribution in wafers produced by different growth techniques.

Recombination-Enhanced Dislocation Motion in SiGe and Ge

In-situstraining experiments on dislocation motion in Ge and Si–5 at% Ge alloy single crystals are performed in a high voltage transmission electron microscope. In comparison with previous results by other methods, the dislocation velocities are found to be enhanced due to a recombination enhancement owing to the excess carrier injection by the electron beam. The reduction in the activation energy of dislocation motion is ascribed to the recombination-assisted kink formation. The kink migration energy is estimated to be 0.7 eV in Ge and 1.5 eV in SiGe.