Experimental studies have demonstrated the importance of the combination of different chemical species at the A-, B-, or X-sites in metal-halide ABX3 perovskites to improve the performance of perovskite solar cells (PSCs). However, from our understanding, further efforts at the atomistic scale are required to unveil the role of alloying in PSCs. Here, we performed a density functional theory investigation on perovskite alloy materials, namely, Cs x MA1–x PbI3, MA x FA1–x Sn0.50Pb0.50I3, and MA x FA1–x PbBr2.50I0.50 (x = 0.00, 0.25, 0.50, 0.75, 1.00). Equilibrium orthorhombic supercell structures were obtained for all systems with distorted octahedral environments, in which the magnitude depends on the chemical species. Besides, energetically stable crystals, in comparison with the parent structures, were found only for Cs x MA1–x PbI3, even though the remaining alloys presented stronger bonds. Furthermore, we addressed the role of the spin–orbit coupling effects to the electronic structure, which was critical to estimate the power conversion efficiency (PCE) with radiative recombinations, e.g., a PCE exceeding 23% was obtained. From our analyses, alloys with Cs content stood out as the best photovoltaic material.

penta-graphene is a quasi-two-dimensional carbon allotrope consisting of a pentagonal lattice in which both sp 2 and sp 3-like carbons are present. Unlike graphene, penta-graphene exhibits a nonzero bandgap, which opens the possibility of its use in optoelectronic applications. However, as the observed bandgap is large, gap tuning strategies such as doping are required. in this work, density functional theory calculations are used to determine the effects of the different number of line defects of substitutional nitrogen or silicon atoms on the penta-graphene electronic behavior. our results show that this doping can induce semiconductor, semimetallic, or metallic behavior depending on the doping atom and targeted hybridization (sp 2 or sp 3-like carbons). in particular, we observed that nitrogen doping of sp 2-like carbons atoms can produce a bandgap modulation between semimetallic and semiconductor behavior. These results show that engineering line defects can be an effective way to tune penta-graphene electronic behavior. Research on 2D materials has gained much attention since the discovery of graphene 1,2. This carbon allotrope that is composed of a hexagonal lattice was demonstrated to possess several exciting features, such as high electrical and thermal conductivity and large mechanical resistance that are aimed at developing the next generation of organic optoelectronic devices 3,4. However, when it comes to optoelectronic applications, graphene has a zero bandgap, which precludes its use, for instance, as active material in solar cells. To overcome this issue, gap opening strategies have been developed 5-7 including the cutting of graphene sheets into graphene nanoribbons 8 , the adsorption of H-adatoms 9 and the use of dopants 10-12. Recently, the effects of such techniques have also been studied in similar 2D materials such as arsenene 13,14 , by means of first principle calculations. When it comes to doping strategies, these are often divided into wet and dry doping methods 15. The former makes use of the spin coating of dopant containing solutions so that charge transfer between graphene and dopant may take place. Dry doping strategies, on the other had, include the electrostatic field doping method, which consists on the application of an electric field perpendicular to the graphene sample. This method, however, cannot be applied to single layers of graphene. A more appropriate strategy in the context of this work is the atom substitution method, which can be performed by means of thermal treatment or plasma doping, for instance. There are a few nature-occurring carbon allotropes, including graphite, fullerenes 16 , and carbon nanotubes 17. Recently, another allotrope was proposed named penta-graphene 18 (see Fig. 1), which has a lattice composed of pentagons that resemble the Cairo pentagonal tiling. It is supposed to present ultrahigh ideal strength even above that of graphene and to be able to withstand temperatures of up to 1000 K 19. Penta-graphene was not synthesized yet, and it is believed t...

The structural and electronic properties of MoS2 sheets doped with carbon line domains are theoretically investigated through density functional theory calculations.

Recently, it was experimentally shown that the performance and thermal stability of the perovskite MAPbI3 were improved upon the adsorption of a molecular layer of caffeine. In this work, we...