Comparison of possible realizations of quantum ratchet intermediate band solar cells

Three fundamentally different approaches for the realization of a quantum ratchet intermediate band solar cell are compared. The quantum ratchet is a mechanism by which an energy loss of excited electrons is turned into an improvement in the efficiency of intermediate band solar cells by reducing carrier recombination in the system. The main requirement for this is to engineer forbidden transitions which can be achieved through vanishing spatial overlap of the wave-functions, spin-selection rules or a momentum mismatch.