Experimental and Theoretical Investigations on the Structural, Electronic, and Vibrational Properties of Cs₂AgSbCl₆ Double Perovskite

Abstract

Despite the rapid development and enormous success of organic–inorganic hybrid halide perovskites (AB′X 3), such as CH3NH3PbI3 as absorbers for perovskite-based solar cells (PSCs), the commercial applications of photovoltaic techniques still face several challenges, such as decomposition when exposed to light and moisture, and lead toxicity. On the other hand, the double perovskites (A 2 B′B″X 6) are derived from the AB′X 3 when half of the octahedrally coordinated B′-cations are partially replaced by the suitable B″-cations. They are attracting attention due to a new design strategy to replace Pb2+ ions with the couple of a monovalent M + ion and a trivalent M 3+ ion, leading to a new family of quaternary double perovskites. In this way, we aim to synthesize and characterize Cs2AgSbCl6 powdered samples, designed for solar cell applications. The crystalline phase and morphological features are investigated by X-ray powder diffraction (XRPD), neutron powder diffraction (NPD), scanning electron microscopy (SEM) in complement with UV–vis spectroscopy, showing a suitable band gap of 2.7 eV. The solution synthesis method proved to be efficient in obtaining polycrystalline-Cs2AgSbCl6 samples in a cubic ordered phase. DFT calculations also provided insights on the vibrational properties of Cs2AgSbCl6, corroborating the experimental data and elucidating the optical activity of Raman and infrared modes.

Isolated [SbCl6]3– Octahedra Are the Only Active Emitters in Rb7Sb3Cl16 Nanocrystals

“…The PL full width at half-maximum (FWHM) of both samples under 3.5 eV excitation follows a nearly identical trend with temperature (Figure S6) that is well reproduced by the expression This expression is typically used to describe the phonon-related homogeneous broadening of the PL peak ( k B is the Boltzmann constant). For both samples the Huang–Rhys factor, S , and the phonon energy, E ph , are respectively found to be ∼60 and ∼18 meV (∼145 cm –1 ), which is fully consistent with the internal vibrational mode of [SbCl 6 ] 3– octahedra, thus further corroborating our hypothesis that the emissive center in the two material systems is the same …”

“…For both samples the Huang−Rhys factor, S, and the phonon energy, E ph , are respectively found to be ∼60 and ∼18 meV (∼145 cm −1 ), which is fully consistent with the internal vibrational mode of [SbCl 6 ] 3− octahedra, thus further corroborating our hypothesis that the emissive center in the two material systems is the same. 46 To provide further insight onto the photophysical mechanisms underpinning the observed T-dependence of the PL, we measured the time-resolved PL as a function of T with E exc = 3.5 and 4.66 eV (Figure 3). Rb 7 Sb 3 Cl 16 NCs show a drastic lengthening of the PL decay time, spanning almost 6 orders of magnitude, independent of the excitation energy (Figures 3a−d and S7).…”

Detailed Structural Features of the Perovskite-Related Halide RbPbI3 for Solar Cell Applications

“…The Debye model is supposed to describe the temperature evolution of the MSDs, as summarized below where such that d s 2 is the intrinsic disorder, θ D is the Debye temperature, m is the atom’s mass, and T , k B , and ℏ keep their usual meaning. 34 , 35 As low-temperature points (<100 K) were not taken, the uncertainty associated with d s 2 is high, when it is considered as a fitting parameter. In order to avoid this, such a parameter was kept equal to zero for all the atoms (Rb, Pb, I1, I2, and I3).…”

Lead-free double perovskites: how divalent cations tune the electronic structure for photovoltaic applications

“…32,45 In the Cs 2 AgSbCl 6 perovskite structure, the Ag–Cl and Sb–Cl bonds are classified as having a transient characteristic. 22 However, the orbitals of the Cs cations do not contribute to the top of the VB or the bottom of the CB. The occupied Cs s and p states are narrow and deep lying in the VB, outside the energy range shown in Fig.…”

“…Reported chloride double perovskites such as Cs 2 AgSbCl 6 and Cs 2 AgBiCl 6 typically have wide indirect bandgaps of 2.54 eV 19 and 2.77 eV, 20 respectively, which are too large for photovoltaic applications. 21,22 Therefore, an increased visible-light absorption efficiency via reduction of the bandgap is required for future applications of these perovskites in optoelectronic technologies. 23,24 Recently, the Cs 2 AgSbCl 6 double perovskite has been reported to have a high decomposition temperature and high stability upon prolonged exposure to air and moisture; therefore, it was proposed as a potential candidate in photovoltaic applications.…”