Modeled performance of triple junction, double heterostructure p+in+ solar cells

Multiple champion solar cells have pin configurations including interdigitated back contact cells, heterojunction with intrinsic thin layer cells, and most recently the 41% efficiency Ga_0.5P/Ga_0.99In_0.01As/Ge cell. The motivation for such structures is not widely understood. This proposed model is based on Shockley's fundamental assumption that open circuit voltage is determined by the splitting of the quasi-Fermi levels as described by the exponential Boltzmann distributions in terms of the optically generated carrier concentrations. For carrier concentrations of 10¹⁵ cm ^-3, the modeled efficiency is 42% for band gap values of 1.8eV, 1.4 eV and 0.9 eV. At 10¹⁷ cm^-3 and 10¹⁹ cm^-3 concentrations, the modeled efficiencies rise to 54% and 65% respectively for band gap values of 1.7 eV, 1.2 eV and 0.7 eV. High generated carrier concentrations can be achieved with low doping levels since carrier lifetimes are inversely proportional to doping levels.