New information on lead-free fully inorganic double alloyed perovskites

The development of lead-free inorganic double-alloy perovskites has revolutionized materials science and industry, according to the journal’s latest research The science of materials.

To study: Unleaded Double Allied Perovskites: An Emerging Class of Materials Derived from Multibody Perturbation Theory. Image Credit: Niethammer Zoltan / Shutterstock.com

The favorable properties such as a higher optical energy band, a high number of charge carriers and a low manufacturing cost have been the fundamental reason for the success of double perovskites in a shorter time. However, there are still some major concerns regarding their use such as phase instability and lead (Pb.) Toxicity.

Double lead-free perovskites

The durability issues have been partially solved by substituting synthetic cesium ions for the organic cations. However, the toxicity of lead remains a drawback and it is essential to address this problem without compromising efficacy.

One suitable method of successfully avoiding this toxicity is to synthesize lead-free inorganic double perovskites primarily due to their low level of toxicity compared to conventional substances. In particular, research has focused on the double perovskite Cs2AgInCl6 due to their environmentally friendly operation and excellent electrical, thermal and mechanical properties. The latest published research focuses on the variation of the carrier-lattice interaction and the optoelectric properties of Cs.2AgInCl6 double perovskite.

(a) Crystal structure of the double perovskite Cs2AgInCl6 and (b) band structure of Cs2AgInCl6 using G0W0 @ HSE06.  Ef is the energy level of fermi.

Figure 1: (a) Crystal structure of double perovskite Cs2AgInCl6 and (b) band structure of Cs2AgInCl6 using [email protected] Ef is the energy level of fermi.

Methods and properties

To quantify the exciton binding energy (EB) and the lifetime of the excitons of different double-allied perovskites, the N-body perturbation theory ([email protected]) and density functional disturbance theory (DFPT) were used.

The initial explanation of photophysical phenomena in perovskite materials was made using the polaronic effect, in particular dealing with electronic excitation and charge mobility. The researcher of the latest study successfully used Fröhlich’s model for the precise calculation of polaron mobility. The next logical step involved the precise calculations regarding the effective mass of the electrons by using the Wannier-Mott approach. This facilitates calculations for the reduced mass.

(a) Electronic contribution to dielectric function and (b) ionic contribution to dielectric function of virgin Cs2AgInCl6 and various alloyed compounds.

(a) Electronic contribution to dielectric function and (b) ionic contribution to dielectric function of virgin Cs2AgInCl6 and various alloyed compounds. Image Credit: Jain, M et al., Materials Science

The estimation of the binding energy was followed by the calculation of the static electronic dielectric constant (ε??) and static ionic dielectric (ε static). This led to the initial calculation of the mobility of charge carriers using the Shockley and Bardeen strain potential model. The final study of the coupling between the phonon and the electron was carried out by the implementation of the Fröhlich polaron model. Each of the steps was performed in accordance with international standards to provide accurate analysis in the research document.

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The researchers said their analysis and results are consistent not only with theoretical concepts but also with previous studies. The value of the effective mass of the electrons, the mass of the hole and the reduced mass were respectively 0.29, 1.07 and 0.23. The static dielectric constant and ionic dielectric constant values ​​were 2.05 and 9.63. These values ​​have been validated by previous studies. A high value of the ionic constant is evidence of a high ionic contribution to the dielectric value.

These constants were then used by the researchers in the standard equations to obtain the upper and lower limit values ​​such as 0.74 eV and 0.03 eV. Such values ​​were an indication of a shorter excitation lifetime of the double perovskites leading to higher quantum yield and phase conversion efficiency.

Pure Cs2AgInCl6 and other alloyed products have isotropic conduction behavior due to the fundamental cubic crystal structure. The value of the effective mass of the hole was about 3 times that of the electron, indicating higher electronic conduction and movement capacity (665.38 cm2V -1 s -1) than the mobility of the hole (30.68 cm2V -1 s -1).

Debye Temperature and Load Carriers

For blank Cs2AgInCl6, the Debye temperature (D) of the effective frequency LO is 215 K. Likewise, the Debye temperature for several allied systems is much lower than the ambient temperature, which implies a significant polaronic influence to limit the mobility of the carriers around room temperature. All values ​​reported by the researchers relate to previous studies describing the accuracy of this difficult study.

The researchers concluded that charge carrier excitations are limited by phonon scattering, which is crucial for the formation of high efficiency perovskite photovoltaic panels. Under ambient conditions, the researchers used the Fröhlich process to find the diffusion of carrier phonons.

In addition, during alloying, we see a substantial improvement in the mobility of holes and electrons. The journal researcher said the findings would help better understand the optoelectronic characteristics and lattice dynamics of these double perovskites.

3(a) Relation between total energy and strain applied along transport direction (z axis) (b) Band energy shifts of VBM and CBm under uniaxial strain for Cs2AgInCl6.

(a) Relation between total energy and strain applied along transport direction (z axis) (b) Band energy shifts of VBM and CBm under uniaxial strain for Cs2AgInCl6. Image Credit: Jain, M et al., Materials Science

In summary, the charge excitation and electron-atom interaction properties of virgin Cs2AgInCl6 and several double-allied perovskites have been explored in depth using first principle calculations. The upper and lower limits of the energy bands of the excitons using the Wannier-Mott method were calculated. As a result, the researchers found that the allied compounds had a longer exciton duration than virgin Cs2AgInCl6, based on the calculation of the longevity of the excitons.

The in-depth analysis in the published research paper completely validated the various first-order electrical and optical properties of double perovskites using multibody perturbation. This research would surely aid not only in the manufacture but also in the continuous improvement of the properties of these substances.

The references

Jain, M., Kumar, M., Bhumla, P., & Bhattacharya, S. (2021, October 23). Unleaded Double Allied Perovskites: An emerging class of materials derived from the theory of multi-body perturbation. The science of materials. From arxiv: https://arxiv.org/abs/2110.12146

Disclaimer: The views expressed herein are those of the author, expressed in a private capacity and do not necessarily represent the views of AZoM.com Limited T / A AZoNetwork, the owner and operator of this website. This disclaimer is part of the terms and conditions of use of this website.

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