講演情報
[24p-P06-15]Analysis of Two Step Photocurrent Generation in GaAsN-Based Intermediate Band Solar Cells Based on Device Simulation
〇(D)Md Faruk Hossain1, Shuhei Yagi1, Hiroyuki Yaguchi1 (1.Saitama Univ.)
キーワード：
solar cell、Intermediate band、External quantum efficiency
Intermediate band solar cell (IBSC) concept has drawn extensive attention for its potential of overcoming the Shockley–Queisser limit of single junction solar cells. In this work, we developed a way of analyzing two-step photocurrent generation process in IBSCs by means of numerical device simulation combined with rate equation analysis, and report simulation results of GaAsN-based IBSCs which have the same layered structure (shown in Fig. 1) as the ones previously fabricated and experimentally investigated [1].
The E+ and E− conduction subbands in the GaAsN layer locate at 1.15 eV and 1.5 eV above the valence band (VB) top, respectively. Silvaco ATLAS TCAD tool is used to simulate the current response to the VB-IB (E−) excitation by an optical beam at a wavelength of 980 nm with a photon flux density of 1×1016 cm-2s-1. In the device simulation, the GaAsN layer is treated as a single gap material having the gap energy corresponding to the IB-VB gap. As shown in Fig. 2(a), experimental results of the voltage dependent external quantum efficiency (EQE) are well reproduced by the simulation with properly adjusted material parameters such as interface recombination rates. Then, rate equations considering transitions between the multiple bands in the GaAsN layer are solved to obtain the change in EQE (delta EQE) caused by adding the second light source (photon flux density is 1.3×1018 cm−2s−1 and photon energy is 0.92 eV), which can excite only the IB to CB optical transition. The voltage dependent delta EQE is calculated based on the rate equation analyses and carrier distribution in the GaAsN layer obtained by the device simulation. It shows excellent agreement with the experimental results (Fig. 2(b)), indicating that the proposed method is effective to discuss the behavior of two step photocurrent generation process in IBSCs.
The E+ and E− conduction subbands in the GaAsN layer locate at 1.15 eV and 1.5 eV above the valence band (VB) top, respectively. Silvaco ATLAS TCAD tool is used to simulate the current response to the VB-IB (E−) excitation by an optical beam at a wavelength of 980 nm with a photon flux density of 1×1016 cm-2s-1. In the device simulation, the GaAsN layer is treated as a single gap material having the gap energy corresponding to the IB-VB gap. As shown in Fig. 2(a), experimental results of the voltage dependent external quantum efficiency (EQE) are well reproduced by the simulation with properly adjusted material parameters such as interface recombination rates. Then, rate equations considering transitions between the multiple bands in the GaAsN layer are solved to obtain the change in EQE (delta EQE) caused by adding the second light source (photon flux density is 1.3×1018 cm−2s−1 and photon energy is 0.92 eV), which can excite only the IB to CB optical transition. The voltage dependent delta EQE is calculated based on the rate equation analyses and carrier distribution in the GaAsN layer obtained by the device simulation. It shows excellent agreement with the experimental results (Fig. 2(b)), indicating that the proposed method is effective to discuss the behavior of two step photocurrent generation process in IBSCs.