A <strong>quantum yield</strong> for a process is the number of times that an event
occurs for every photon absorbed by the system. The quantum yield for
charge injection is the ratio of the number of photons that get
injected into the semiconductor to the total number of photons absored
by the dye (which is equal to the total number of electrons that could
possibly be injected into the semiconductor).  This expresses the
efficiency of charge injection.