Revealing the role of Pb²⁺ in the stability of organic–inorganic hybrid perovskite CH₃NH₃Pb_1−xCd_xI₃: an experimental and theoretical study

Abstract

This paper presents the synthesis of organic-inorganic hybrid perovskite CH3NH3Pb1-xCdxI3. The effect of incorporating Cd(2+) or Pb(2+) on the stability of the perovskite structure was analysed from a theoretical and experimental viewpoint. The XRD results showed that the tetragonal perovskite structure was formed for x values of up to 0.5, which seems to indicate that the presence of a considerable amount of Pb(2+) is necessary to stabilise the structure. In turn, UV-Vis spectroscopy showed how the presence of Cd(2+) led to a reduction in the optical band gap of the perovskite structure of up to 9% for CH3NH3Pb0.5Cd0.5I3 with regard to the MAPbI3 structure. Moreover, periodic-DFT calculations were performed to understand the effect of the increased concentration of Cd on the structural and electronic properties of MAPbI3 perovskites. The analysis of both the ELF and the non-covalent interaction (NCI) index show the important role played by the Pb(2+) ions in stabilizing this kind of hybrid perovskite structures. Finally, the DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy. The theoretical band gap values decreased as the concentration of Cd increased.

Hybrid Perovskite, CH3NH3PbI3, for Solar Applications: An Experimental and Theoretical Analysis of Substitution in A and B Sites

“…Journal of Nanomaterials [6,38]. Thus, the contribution of Cd s-states is also included in Figure 7 and it is shown that the contribution of the s-states of the Cd to the origin of the CB plays a fundamental role in the decrease in the band gap, as reported elsewhere [38].…”

“…The values are 1.5, 2.2, and 1.19Å for NH 4 + , I − , and Pb 2+ , respectively. In turn, the effective ionic radius of [CH 3 NH 3 ] + was calculated according to a rigid sphere model with free rotation of its centre of mass, as reported in the literature [38]. The value obtained is 1.74Å.…”

“…From the results expounded above, the A 0.25 MA 0.75 PbI 3 perovskite was selected for exploring theoretically the changes in the structural and electronic properties of the material when the Pb is substituted by Cd. This metal was selected because it is known to decrease the band gap in MAPbI 3 perovskites [6,38] when it is used in B position as an alternative to Pb. Thus, an analysis was performed into the effect of increasing the concentration of Cd on the structural and electronic properties of (A) 0.25 (MA) 0.75 Pb 1−x Cd x I 3 with = 0.00, 0.25, 0.50, 0.75, and 1.00.…”

The Role of Surfactants in the Stability of NiO Nanofluids: An Experimental and DFT Study

“…DFT‐periodic calculations were performed by using the Vienna ab initio simulation package (VASP) with the projector‐augmented wave (PAW) method . The number of plane waves in VASP was controlled by a cutoff energy, set in our calculations to E cut =500 eV, to satisfactorily describe the system . The electron exchange and correlation were treated within the generalised gradient approximation (GGA) .…”

Perovskite Solar Cells: Progress and Advancements

“…the devices are exposed to moisture, continuous illumination, thermal-stress and oxygen [40,[107][108][109][110][111][112][113]. The basic degradation mechanism in PSCs is the breakdown of perovskite material under moisture or heat stress, which results in the segregation of MAPbI3 into its constituents PbI2 and MAI [114][115][116]. It is summarized as: CH3NH3PbI3 → PbI2 + CH3NH2↑ +HI↑ The perovskite CH3NH3PbI3 thin films are found to undergo decomposition under thermal stress at a temperature between ~100 °C [117] and 140 °C [118]; the decomposition rate increases further as the temperature is increased [119].…”