Analysis of two-step photocurrent generation in GaAs:N-based intermediate band solar cells with utilization of device simulation

We developed a novel approach to analyze the two-step photocurrent generation process in intermediate band solar cells (IBSCs) by means of numerical device simulation combined with rate equation analysis. An IBSC having a GaAs:N intermediate band (IB) absorber with the same layered structure as experimentally investigated in our previous work is modeled, and its characteristic behavior of external quantum efficiency (EQE) is successfully simulated with the utilization of Silvaco-Atlas software. The simulated results gave new insights into the material parameters of the device, such as trap states and interface recombination velocity, and revealed that an electron-blocking layer adjacent to the IB absorber plays a significant role in confining the electrons in the IB state, which is the main prerequisite for efficient two-step photocurrent generation. Change in EQE (ΔEQE) induced by additional light illumination of which energy is below the valence band–IB gap is analyzed as an evaluation metric of two-step photocurrent generation based on a rate equation analysis. The integrated electron concentration in the GaAs:N absorber layer is calculated from the simulation results and is used as an input parameter for the rate equation analysis. As a result, the bias voltage-dependent ΔEQE of experimentally investigated IBSC is well reproduced, indicating that the proposed method can be a useful approach for a better understanding of IBSC operation physics and designing more efficient devices.