Oxygen and Carbon Precipitation in Multicrystalline Solar Silicon

Abstract

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.