Enhancing the efficiency of the intermediate band solar cells by introducing: carrier losses, alloying and strain

Abstract

A detailed balance model is used to determine the efficiency of intermediate band solar cell including carrier losses from the intermediate band. The effect of the energy gap of the host semiconductor is examined as a function of the intermediate band position in the energy gap and the host semiconductor energy gap. Generally the optimal intermediate band level decreases within the energy gap to mitigate the carrier losses, and carrier losses are less detrimental to small energy gap materials. We therefore focus on the role of carrier losses in wide bandgap semiconductor intermediate band solar cell systems, such as the GaN semiconductor with an Mn impurity band. Experimentally Mn acceptor level in the GaN energy gap is 1.8 eV above the valence band, which is 199 meV off the ideal intermediate band and reduces the efficiency to 21.36%. We demonstrate how carrier losses can be introduced into the system to shift the optimum IB position. Introducing carrier losses shifts the optimal intermediate band position to 1.8 eV above the valence band and increases the efficiency to 23.41%. We compare this to the effect of alloying GaN and introducing biaxial strain to shift the effective position of the Mn impurity band on the efficiency.