Chapter One - The Physics of Industrial Crystalline Silicon Solar Cells

Abstract

Abstract Solar cells made from multi- or monocrystalline silicon wafers are large-area semiconductor p–n junctions. Technically, solar cells have a relatively simple structure, and the theory of p–n junctions was already established decades ago. The generally accepted model for describing them is the so-called two-diode model. However, the current–voltage characteristics of industrial solar cells, particularly of those made from multicrystalline silicon material, show significant deviations from the established diode theory. These deviations regard the forward and the reverse dark characteristics as well as the relation between the illuminated characteristics and the dark ones. In the last few years, it has been found that the characteristics of industrial solar cells can only be understood by taking into account local inhomogeneities of the dark current flow. Such inhomogeneities can be investigated by applying local imaging techniques like lock-in thermography and luminescence imaging. Meanwhile, based on these and other investigations, the basic properties of industrial silicon solar cells are well understood. This contribution first summarizes the established theory of the operation of solar cells, which generally assumes homogeneous current flow. Then the predictions according to this theory are compared to the experimentally measured characteristics of industrial solar cells, which largely deviate from these predictions. In the following sections, the most important experimental and theoretical results explaining these deviations are introduced, leading to the present state of physical understanding of the dark and illuminated characteristics of multicrystalline industrial solar cells.