Model for intermediate band solar cells incorporating carrier transport and recombination

Abstract

A model for intermediate band solar cells is presented to assess the effect of carrier transport and recombination (CTR) on the efficiency of these devices. The model includes dependencies of physical parameters including optical absorption, carrier lifetime, and carrier transport on the density of intermediate band electronic states. Simulation results using this model indicate that conversion efficiency degrades when the net carrier recombination lifetime is small (range of nanoseconds) or when the device length is long relative to carrier drift length. The intermediate band solar cell model provides a method of determining realistic conversion efficiencies based on experimentally measurable input parameters for CTR. The incorporation of CTR provides insight on the dependence of optimal density of states and energetic position of the intermediate band based on carrier lifetime and mobility. The material ZnTeO (EG=2.3 eV, EI=1.8 eV) is used as a numerical example for the intermediate band solar cell model, where conversion efficiency drops from 30.36% to 19.4% for a 10 μm long device for a recombination lifetime decrease from 1 μs to 5 ns. The optimal impurity concentration is determined to be 1018 cm−3 for an optical absorption cross section of 10−14 cm2. The conversion efficiency of a ZnTe solar cell with a total recombination lifetime of 10 ns is calculated to increase from 14.39% to 26.87% with the incorporation of oxygen.