CdS-based intermediate band solar cells (IBSC): A numerical investigation using SCAPS-1D

Intermediate band solar cells (IBSC) have drawn significant attention recently due to their potential to surpass the Shockley-Queisser efficiency limit. Herein, we investigate the suitability of a CdS film as the p+/IB/n+ layers within the IBSC structure using numerical solutions. Initial benchmarking with the theoretically reported device in the literature is performed by incorporating optimal, non-overlapping sub-bandgap absorption using a custom ASCII file. It is observed that the simulated device can effectively harness energy from low-energy red light to high-energy violet light by employing three optical transitions. The results confirm that a thickness of 1 µm and a donor concentration of 10¹⁴ cm^-3 are optimal for the absorber to reach the upper limit efficiency of 46%, with both the p+ and n+ layers being 0.1 µm thick with an acceptor/donor density of 10¹⁸ cm^-3, respectively. The field near the junction is shown to amplify, and the depletion width is widest at 0.97 µm, approximating the thickness of the absorber at this donor level. Additionally, inadequate impurity-host atom substitution could lead to the formation of discrete levels, which are detrimental at high defect concentrations. A defect concentration of 10¹⁸ cm^-3 counteracts the contribution from generation, thus detrimentally depreciating the overall efficiency.