Optoelectronic properties of novel layered materials under encapsulation: 2D Copper Iodide and Silver Iodide

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Many novel freestanding two-dimensional materials can be stabilized when placed over a proper substrate or put under encapsulation. Among the different possibilities, graphene and h-BN are commonly used due to their availability and compatibility. In that scenario, it is important to understand how the possible interactions between the core and substrate/encapsulating layers as well as the lattice mismatch affect the optoelectronic properties of the core material. In this work, we use ab initio calculations to study the structural and optolectronic properties of the recently synthesized 2D CuI and AgI layers, which are stabilized under graphene encapsulation (Mustonen et al. (2022)). In addition, the possibility of h-BN encapsulation is also explored. We find that the optoelectronic properties of the core materials are greatly preserved under encapsulation—especially under h-BN. Their bandgaps suffer small variations that mainly originate from the internal strain that results from supercell relaxation. We also see a rehybridization of the electronic bands from the core material whenever they cross or lie close to bands from the encapsulating layers, as expected. This effect is particularly strong for graphene encapsulation. The optical absorption profiles show a combination of features coming from the spectra of the isolated layers with minor modifications introduced by these effects. In particular, a strong and broad absorption is seen in the UV range when using h-BN. Finally, we study a possible CuI-AgI heterobilayer, both isolated and under encapsulation. Interestingly, the structure presents a type-II band alignment that is well preserved under encapsulation, with potential applications in novel photovoltaic devices.