The Role of Inhomogeneities for Understanding Current–Voltage Characteristics of Solar Cells

All solar cells show more or less inhomogeneous electronic properties. This holds in particular for multicrystalline silicon cells, where local differences of the lifetime of more than an order of magnitude exist. This contribution explains how these inhomogeneities can be imaged and quantified, and the physical origins and the efficiency degradation potential of J 01 -, J 02 -, and ohmic inhomogeneities are reviewed. It is found that J 02 and ohmic currents are always highly localized, in contrast with J 01 currents. Hence, for describing most of the area of silicon solar cells, a one-diode model is sufficient, but J 02 and ohmic currents reduce the efficiency at low illumination intensity. Moreover, the physical origins of known prebreakdown phenomena are reviewed and a new breakdown type dominating in monocrystalline silicon cells is proposed.