Multi-scale approach to the modeling of QD based intermediate band solar cells (IBSC): (a) constituent materials of individual QD is treated at the atomistic quantum mechanical level [59,62,66], (b) array of QD as an absorbing material of the IBSC is treated at semi-empirical mesoscopic quantum mechanical level [20,72], (c) using methods of quantum engineering from (b) the material with new targeted functionality is designed [119], (d) such QD array material is described and the device level by drift diffusion model informed from stages (b and c) in order to predict the IV characteristics and efficiencies of IBSC [20,73], (e) the design is ultimately leading to the fabrication of actual CPV IBSC module consisting of 4 IBSC [22,122].