Oxygen impurity in crystalline silicon

Abstract

Oxygen belongs to the most important impurities in many types of solar silicon. Interstitial oxygen is already incorporated in a supersaturated state during crystal growth. Subsequent thermal treatment during solar cell manufacturing leads to its precipitation which degrades the lifetime of minority carriers in solar cell material and also the solar cell efficiency. Oxide precipitate nuclei are formed already during crystal cooling. A special form of oxygen precipitation is the generation of thermal donors which enhance the free carrier concentration and in this way degrade the lifetime of minority carriers. Controlling of oxygen precipitation for optimization of solar cell efficiency involves controlling of all important factors affecting the nucleation and growth of oxygen-related defects. Therefore, this chapter deals with the basic understanding of oxygen precipitation and thermal donor formation, its characterization and measurement, and its impact on solar cell material and solar cell performance. The interaction of intrinsic point defects, light elements, and dopants with oxygen and its impact on precipitation is also discussed.