Role of Impurities in Solar Silicon

Gianluca Coletti1, Daniel Macdonald2 and Deren Yang3
1ECN Solar Energy, Westerduinweg 3, Petten, the Netherlands
2School of Engineering, College of Engineering and Computer Science, The Australian
National University, Canberra, ACT, Australia
3State Key Lab of Silicon Materials, Zhejiang University,

Hangzhou, China

3.1 Introduction

Impurities in crystalline silicon can be classified into two categories, dopants and con­taminants. Generally, dopants are intentionally added to modulate the resistivity, while contaminants are unintentionally incorporated during the material processing.

The quality of silicon depends on the purification processes associated with the manu­facturing of the polysilicon feedstock starting from metallurgical silicon (see Chapter 2). However, during the entire manufacturing chain that leads to solar cells, both purification and contamination processes take place. In Section 3.2 the different sources of impurities and the related refinement processes are discussed. The impurity segregation mechanism during the crystallization of silicon ingots is reported in Section 3.3. In Section 3.4 the impact of metals, dopants and light elements on the solar-cell performance are discussed separately. The definition for solar silicon is discussed in Section 3.5.