InGaN Quantum Dots for Intermediate Band Solar Cells
Luc Robichaud1& Jacob J. Krich1,2
1Department of Physics, University of Ottawa, Ottawa, ON, Canada
/2School of Electrical Engineering and Computer Sciences, University of Ottawa, Ottawa, ON, Canada

We study the potential efficiency of a wurtzite InGaN/GaN quantum dot system as an intermediate band solar cell. With the deep band offsets of the InGaN system, we show that the detailed balance formalism is equivalent to a ratchet band system and show the optimal efficiencies. These detailed balance results provide targets for the energy levels of the quantum dots. We use a k.p electronic structure model, including the effects of strain, to design the size and alloy fraction of dots to approach the optimal energy levels. Strain-driven piezoelectric fields separate the electron and holes states inside the quantum dot, requiring small quantum dots in order to have significant optical absorptions. In this case of small dots, we find 1-sun optimal efficiencies over 42% with required indium fractions of 70-80%. We discuss the effects of free carriers to screen the piezoelectric fields and further increase the potential efficiency.