ABSTRACT
Recent attempts have been made to increase the efficiency of solar cells by introducing an impurity energy level in the semiconductor band gap that absorbs additional lower energy photons [1–3]. The question has been raised [4, 5] whether these cases have their efficiency lim ited too by the Shockley and Queisser (SQ) model [6] for ideal cells, as it is the case for conventional solar cells. In this chapter an ideal solar cell with an intermediate energy level or band within the semiconductor gap is analysed presenting an efficiency well above the one permitted by the SQ model. What we precisely mean by ideal solar cell is developed along the text in seven conditions labeled IC1 to IC7.
