ABSTRACT
Graphene-based ternary BNC materials have been widely explored for the fabrication of gas sensors because of their various two-dimensional conjugated structures, high conductivity and large specific surface areas. To understand the essential physics and gas sensing properties, we focus on a sheet with equal concentration of C and BN, i.e. a BNC2 sheet. Using density functional theory, we have explored the effects of doping of an aluminium (Al) atom on the structural and electronic properties of a ternary BNC monolayer. We have studied the adsorption mechanism of various gas molecules such as CO, CO2, NO, NO2, SO2, and SO3 on BNC2 and Al@BNC2 MLs. Doping of the Al atom in BNC2 changes the structural as well as electronic properties of the host dramatically. The large-sized Al atom protrudes out from the BNC2 ML. The induced defects due to doping of the Al atom in BNC2 reduce the band gap of the BNC2 ML and enhance the reactivity of the BNC2 ML. The adsorption of CO, CO2, NO, NO2, SO2, and SO3 gas molecules shows higher interaction towards the Al@BNC2 ML as compared to the BNC2 ML. Among all the gas molecules, the maximum interaction of NO2 gas molecules is found with the Al@BNC2 ML. Adsorbed gas molecules act as charge acceptors from both the MLs. The improved conductivity of the Al@BNC2 ML as compared to BNC2 with the adsorption of gas molecules offers the basis for the development of ternary BNC-based gas sensors.
ABSTRACT
We have explored the structural, electronic, charge transport, and optical properties of lead-free 2D hybrid halide perovskites, MASnBr3 and Ruddlesden-Popper perovskites, BAMASn2Br7 monolayers. Under density functional theory (DFT) calculation, we applied mechanical strain, i.e., tensile and compressive strain up to 10% in both cases. The mechanical strain engineering technique is useful for a tuned bandgap of 2D MASnBr3 and 2D BAMASn2Br7. The calculated carrier mobility for the electron is 404 cm2 V-1 s-1 and for the hole is up to 800 cm2 V-1 s-1 for MASnBr3. For BAMASn2Br7 the highest carrier mobility is up to 557 cm2 V-1 s-1 for electrons and up to 779 cm2 V-1 s-1 for the hole, which is 14% and 24% higher than the reported lead-iodide based perovskites, respectively. The calculated solar cell efficiency of 2D MASnBr3 is 23.46%, which is 18% higher than the reported lead-based perovskites. Furthermore, the optical activity of the 2D MASnBr3 and 2D BAMASn2Br7 shows a high static dielectric constant of 2.48 and 2.14, respectively. This is useful to show nanodevice performance. Also, 2D MASNBr3 shows a high absorption coefficient of 15.25 × 105 cm-1 and 2D BAMASn2Br7 shows an absorption coefficient of up to 13.38 × 105 cm-1. Therefore our theoretical results suggest that the systems are under mechanical strain engineering. This is convenient for experimentalists to improve the performance of the 2D perovskites. The study supports these materials as good candidates for photovoltaic and optoelectronic device applications.
ABSTRACT
Two-dimensional (2D) hybrid halide perovskites have been scrutinized as candidate materials for solar cells because of their tunable structural and compositional properties. Results based on density functional theory demonstrate its thickness-dependent stability. We have observed that the bandgap decreases from the mono- to quad-layer because of the transformation from 2D towards 3D. Due to the transformation, the carrier mobility is lowered with the corresponding smaller effective mass. On the other hand, the multilayer structures have good optical properties with an absorption coefficient of about 105 cm-1. The calculated absorption spectra lie between 248 nm and 496 nm, leading to optical activity of the 2D multilayer CH3NH3PbI3 systems in the visible and ultraviolet regions. The strength of the optical absorption increases with an increase in thickness. Overall results from this theoretical study suggest that this 2D multilayer CH3NH3PbI3 is a good candidate for photovoltaic and optoelectronic device applications.
