Detailed balance and reciprocity in solar cells

The limiting efficiency of photovoltaic devices follows from the detailed balance of absorption and emission of a diode according to the Shockley–Queisser theory. However, the principle of detailed balance has more implications for the understanding of photovoltaic devices than only defining the efficiency limit. We show how reciprocity relations between carrier collection and dark carrier injection, between electroluminescence emission and photovoltaic quantum efficiency and between open circuit voltage and light emitting diode quantum efficiency all follow from the principle of detailed balance. We also discuss the validity range of the Shockley–Queisser limit and the reciprocity relations. Discussing the validity of the reciprocity relations helps to deepen the understanding of photovoltaic devices and allows us to identify interrelationships between the superposition principle, the diode ideality and the reciprocity relations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)