Type-I Graphene/Si Quantum Dot Superlattice for Intermediate Band Applications

The most important loss mechanism in single junction solar cells is the inability to convert photons with energies below the bandgap to electricity. Due to quantum confinement, graphene-based quantum dots (QDs) provide a means to create an intermediate band (IB) in the bandgap of semiconductors to absorb sub-bandgap photons. In this work, we introduce a new type-I core/shell-graphene/Si QD for use in all Si-based intermediate band solar cells (IBSCs). Slater-Koster Tight-Binding method is exploited to compute the ground state and the band structure of the graphene/Si QD. The ground state is obtained 0.6 eV above the valance band (VB), which is suitable for creating IB between the conduction band and VB of Si. A superlattice (SL) of this QD is created and the mini-band formation in SL is investigated by varying the inter-dot spacing between QDs. A mini-band with roughly 0.3 eV bandgap is observed in the well-aligned and closely packed SL. This SL is embedded in the intrinsic region of the conventional Si-based solar cell. The mini-band in SL works as an IB in the solar cell and results in increased photon absorption. As a result, carrier generation rate improves from 1.48943×1028 m-3s-1 to 7.94192×1028 m-3s-1 and short circuit current density increases from 211.465 A/m2 to 364.19 A/m2.