Electronic and optical properties of lead‐free double perovskites A2BCl6 (A = Rb, Cs; B = Si, Ge, Sn) for solar cell applications: A systematic computational study

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Electronic and optical properties of lead-free double perovskites A2BCl6 (A = Rb, Cs; B = Si, Ge, Sn) for solar cell applications: A systematic computational study

In this report, we have studied lead-free perovskite materials A2BCl6 (A = Rb, Cs; B = Si, Ge, Sn) using the DFT technique. DFT-based global descriptors of perovskite materials are computed and analyzed. Our results reveal that Rb2SiCl6 is the most suitable material among the studied compounds for solar cell applications. Other parameters, namely, tolerance factor, optical properties, and IR and Raman spectra of A2BCl6, are also reported.


Abstract

In recent years, lead-free double perovskite materials have attracted much attention due to their probable applications in photovoltaic and optoelectronic devices. In this work, the electronic and optical properties of lead-free double perovskites A2BCl6 (A = Rb, Cs; B = Si, Ge, and Sn) are studied using density functional theory (DFT) methodology. The result shows that the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps of these compounds vary between 0.524 and 0.919 eV, which agrees with the previously reported data. HOMO-LUMO gap for Rb2SiCl6 is observed as 0.919 eV, which falls in the optimal energy gap range, that is, 0.9 to 1.6 eV for double perovskite material. Conceptual DFT-based descriptors—molecular hardness, softness, electronegativity, electrophilicity index, and dipole moment of these compounds—are studied. The tolerance factor of A2BCl6 is observed in the range of 1.00 to 1.26. Rb2SnCl6 is almost a perfect fit with a value of 1.00. Cs2SiCl6 shows the maximum value of the refractive index and dielectric constant. Optical electronegativity is found between 0.178 and 0.246 eV. The suitable band gap and high value of the refractive index and dielectric constant make double perovskites A2BCl6 effective for solar cells and optoelectronic devices.

A theoretical adsorption study of the inner‐core and outer‐core hydrated alkali metal cation–circumcoronene complexes

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A theoretical adsorption study of the inner-core and outer-core hydrated alkali metal cation–circumcoronene complexes

The cation radius along with the microhydrated environment are the key factors for the (micro)hydrated alkali cations interacting the circumcoronene surface. It was found that balance between M+–π interactions, M+–water complexation, and the hydrogen bonding of water to the π-system govern the formation mechanism of the cation–π complexes in solution, favoring the outer-sphere solvated Li+ and Na+–πCC complexes and the inner-sphere solvated K+–πCC complexes.


Abstract

Cation-π interactions are theoretically investigated for alkali metal cation (M+)-circumcoronene (CC) complexes (M = Li, Na, K), in gas phase and in aqueous solution with consideration of micro- and global solvation models using the DFT/PBEh-3c-RI/TZVP method. The solvent effect on the M+–CC energy interaction regarding the cation size and the stability of inner- and outer-sphere [M(H2O) n ]+–CC complexes are calculated by means of geometry optimizations and potential energy (PE) curves. The PE curves, calculated as a function of perpendicular distance of M+ to the CC plane, predicted one energy minimum for each of the isolated M+–CC complexes. However, for microhydrated complexes, two minima assigned to two different surface complexations were obtained. Microhydrated Li+ and Na+ favored outer-sphere complexation while inner-sphere complexation was found more stable for microhydrated K+. These results illustrate nicely the key role, which the cation radius plays for the polarization of the water molecules and the aromatic system.

Incorporation of graphene oxide to metal‐free phthalocyanine through hydrogen bonding for optoelectronic applications: An experimental and computational study

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Incorporation of graphene oxide to metal-free phthalocyanine through hydrogen bonding for optoelectronic applications: An experimental and computational study

Graphene oxide was attached to imidazole substituted metal-free phthalocyanine at low processing times. The optoelectronic properties were studied experimentally and theoretically. The results suggest improved nonlinear optical properties although the conjugation was accomplished with hydrogen bonding without covalent attachment.


Abstract

This paper focuses on incorporation of graphene oxide (GO) to metal-free phthalocyanine (MPc) through only hydrogen bonding and π-π stacking. Briefly, Pc-GO composites at various concentrations were prepared by self-assembly method. The processing time was kept below 10 min to avoid covalent attachment and we aimed at answering the research question of what will happen if the conjugation is realized only through hydrogen bonding under extremely limited processing times. The as-prepared MPc-GO composites were characterized by Fourier transform infrared (FT-IR), UV-Vis, scanning electron microscope (SEM), and fluorescence analysis. We report that the interaction between MPc and GO could immediately be initiated upon mixing of corresponding solutions. Also, complete conjugation by hydrogen bonding and π-π stacking could be reached even only in 5 min of sonication time. In addition, it was also determined that the prepared MPc-GO composites are stable at room conditions and during dilution. Finally, the optoelectronic properties of MPc and MPc-GO composites were also investigated experimentally and theoretically. Both experimental and theoretical results suggest that MPc-GO composites exhibit improved optoelectronic properties as compared to MPc, even though the conjugation of GO to MPc was only via hydrogen bonding without covalent attachment.