This paper presents a combination of numerical and experimental methods used to characterize defect clusters in multicrystalline silicon solar cells.

Multicrystalline silicon wafers used for solar cells exhibit defect clusters--localized crystal defects in and near grains of some specific orientations. Defect clusters are also dominant sites for impurity precipitation, and they remain ungettered and unpassivated through the solar cell processing. This paper describes characteristics of defect clusters, and shows, through theory and experiment, that defect clusters typically lower cell efficiency by 3 to 4 absolute percentage points. To recover this efficiency loss, it is necessary to getter precipitated impurities.

Our analyses show that defect clusters can lower the efficiency of multicrystalline silicon (mc-Si) solar cells by 2 to 4 absolute percentage points. This large loss can be recovered if impurities precipitated at the defect cluster sites can be gettered. We describe a new technique for gettering precipitated impurities.

The world of today must face up to two contradictory energy problems: on the one hand, there is the sharply growing consumer demand in countries such as China and India. On the other hand, natural resources are dwindling. Moreover, many of those countries which still possess substantial gas and oil supplies are politically unstable. As a result, renewable natural energy sources have received great attention. Among these, solar-cell technology is one of the most promising candidates. However, there still remains the problem of the manufacturing costs of such cells. Many attempts have been made to reduce the production costs of “conventional” solar cells (manufactured from monocrystalline silicon using diffusion methods) by instead using cheaper grades of silicon, and simpler pn-junction fabrication. That is the ‘hero’ of this book; the heterojunction solar cell.

ISTC/CSTIC is an annual semiconductor technology conference covering all the aspects of semiconductor technology and manufacturing, including devices, design, lithography, integration, materials, processes, manufacturing as well as emerging semiconductor technologies and silicon material applications. ISTC/CSTIC 2009 was merged by ISTC (International Semiconductor Technology Conference) and CSTIC (China Semiconductor Technology International Conference), the two industry leading technical conferences in China, and consisted of one plenary session and nine technical symposia. This issue of ECS Transactions contains 159 papers from the conference.