Limiting Efficiencies of Intermediate Band Solar Cells in Tandem Configuration

Abstract

It is necessary to devise innovative techniques to design new high-performance tandem solar cells to meet increasing energy needs. In this study, the theoretical efficiency of intermediate band solar cells (IBSCs) was increased by integrating them with tandem solar cells to produce intermediate band tandem solar cells (IBTSCs). The spectral splitting analysis indicated that the efficient absorption of sub-photon energies was necessary to ensure optimal performance of the IBSCs at each junction of the IBTSC. For this calculation, we assumed all absorption of sub-photon energies are unity. In addition, we applied the variation of absorptivity to the detailed balance limit of a double-junction (DJ) IBTSC. Furthermore, we included the impact of series and shunt resistances of a typical DJ IBTSC to investigate the variations in electrical parameters (short circuit current, open circuit voltage). The performance efficiency also depended on the illumination concentration due to the charge carrier transitions at each junction. We analyzed this aspect to determine the overall performance of the IBTSCs. We replaced the IBSC in the bottom junction with a single-junction solar cell to explore the potential of diverse tandem configurations. DJ IBTSCs achieved a limiting efficiency comparable to that of six-junction solar cells, despite the lower number of junctions. It was challenging for these cells to exhibit optimal performance because of the inefficient spectrum management in the bottom junction. It was concluded that full illumination concentration was required to achieve optimal performance in both junctions of the IBTSC.