Self-consistent drift-diffusion analysis of intermediate band solar cell (IBSC): Effect of energetic position of IB on conversion efficiency

The intermediate band solar cell (IBSC) has been intensively investigated both experimentally and theoretically. Numerical analyses based on the detailed balance method are performed to search for the best suitable candidates of material combination for IBSC and the operation conditions. Analytical treatment of drift-diffusion equations has also been reported under limited approximations. However, to study the device characteristics, self-consistent treatments of both the carrier continuity equations and the Poisson equation are required. In this work, we report on the dependence of conversion efficiency on energetic position of IB and on the concentration by using 1-D self-consistent drift-diffusion simulator which we developed for GaAs based solar cell with InAs quantum dots. The dependence of the efficiency on energetic position of IB above the midgap of GaAs was calculated for 1, 10, 100 and 1000 suns conditions with and without doping in IB region. The optimal IB position shifted to lower energies with increase of concentration in the case of intrinsic IB region. While, in the case of doped IB region, the optimal IB position was almost fixed at 0.95eV. If, however, the IB was set in the middle of the energy gap of GaAs, efficiencies showed lower values with higher concentrations. This is because, according to our present model, very few photons contribute to the optical transition (generation) in CB-IB and most photons are absorbed in VB-IB transitions such that there is a large mismatch in the generation-recombination rates in these transition paths.