Modelling of Intermediate Band Solar Cells: Quantum Dot or Impurity Band — The effect of inhomogeneous broadening

A detailed balanced approach was used to model Intermediate Band (IB) Solar Cells (SCs) in which the IB is a band comprised of either Quantum-Dots (QDs) or Impurity Atoms (IAs). A model assuming identical QDs or IAs with no carrier losses was derived [1] and has a peak efficiency of 63.24% for a bandgap of 1.95 eV with the IB positioned either 1.24 eV above the valence band or below the conduction band. The effect of inhomogeneities in the QDs or IAs is introduced by incorporating an inhomogeneous broadening of the IB and the homogeneous broadening describing life-time broadening effects is also introduced. A Gaussian inhomogeneous broadening of the ground state is considered. The inhomogeneous broadening removes the density of distribution from the ideal peak position so reduces efficiency while the homogeneous broadening allows more photons to be able to interact with the ideal peak energy thereby increasing the efficiency. The interplay between these two effects allows the efficiency in realistic IBs to remain close to the ideal values.