All-inorganic halide perovskites are considered as favorable materials for various electronic applications because of their superior functionality and stability. In this study, the inorganic rubidium lead-bromide (RbPbBr3) perovskite has been integrated as a resistive switching (RS) layer in the Al/RbPbBr3/indium tin oxide/polyethylene terephthalate flexible structure and exhibits both bipolar (memory) switching and threshold switching functions. The threshold switching appears for a low compliance current (CC), whereas the memory switching is initiated by setting a higher CC. The resistive memory switching operations along with multilevel programming, moderate endurance, and retention performance show the reproducible and reliable nonvolatile high-density memory feature. The robustness and mechanical flexibility are established by uniform current–voltage curves under various bending diameters and flexing cycles. Also, the first principle density functional theory calculations demonstrate the contribution of each element in the conduction band and valence band of RbPbBr3 with a direct band gap (2.24 eV). Finally, a mechanism in combination with the formation/annihilation of a metal filament and a Br– ion vacancy filament is proposed to explain the RS behavior.

No abstract

The instability of organic-inorganic hybrid halide perovskites due to light, heat, and moisture restricts them for practical use despite having most suitable photovoltaic properties and higher power conversion efficiency. Several methods such as surface engineering, carbon electrode utilization, and optimization of the components are applied to increase the stability; still, it is far from the practical implementation. Moreover, the toxicity of Pb in most of the efficient hybrid halide perovskites is another major issue. It motivates us to search for a stable and Pb free perovskite solar cell. Hence, a systematic investigation within density functional theory has been made on the structural, electronic, and optical properties of RbMI 3 compounds (where M = Ge and Sn). The structural properties such as lattice parameters, formation energy are calculated. The calculated negative formation energy confirms the chemical stability for both compounds. The electronic properties like partial density of states, band structures with Perdew-Burke-Ernzerhof, Tran-Blaha modified Becke-Johnson (TB-mBJ) and HSE06 are discussed. Band gaps are calculated for RbGeI 3 (2.645 eV) and RbSnI 3 (2.544 eV) with TB-mBJ potential, which is proved to estimate the band gap values accurately for inorganic solids. SOC influences the conduction band minimum without any changes in the valence band maximum and thus reduces band gaps to 2.021 for RbGeI 3 and 1.865 eV for RbSnI 3 . The optical properties like the real and imaginary part of the dielectric constants, absorption coefficients, refractive indices, and reflectivities have also been discussed. Further, transport properties like effective masses, binding energy of excitons, and spectroscopic limited maximum efficiency (SLME) are calculated for both RbMI 3 compounds. The excitons for both structures are found to be Frenkel type. SLME for RbGeI 3 and RbSnI 3 having the thickness of 0.5 μm at a temperature of 300 K are found as 16.5% and 18%, respectively. Finally, the possibility of RbGeI 3 and RbSnI 3 in the solar cell configuration with TiO 2 as the hole transporting material have been explored.

Entirely inorganic perovskites have attracted enormous attention of late owing to their outstanding applications in optoelectronics including highly stable perovskite solar cells. In-depth understanding of the optoelectronic and transport properties of such materials are vital for practical implementation of the same. The carrier transport properties of the electronic devices based on perovskite materials significantly depend on the effective mass of the respective charge carriers. Here, we have performed first principle calculations with FP-LAPW method for the orthorhombic rubidium lead halide structures (RbPbX 3 , where X I,Br,Cl) to study the optoelectronic and transport properties. The effective mass of electron (hole) is found to be minimum for RbPbBr 3 (RbPbI 3 ), suggesting an efficient transport of electrons (holes) in the corresponding materials. Our calculated values such as the dielectric constants, refractive indices, absorption coefficients and reflectivities show good agreement with reported experimental data. To the best of our knowledge, ab-initio study of electronic and optical properties of RbPbBr 3 & RbPbCl 3 in orthorhombic phase (NH 4 CdCl 3 type structure) is reported for the first time.

No abstract

No abstract

TiO2 has tremendously drawn the attention of researchers from the photocatalytic to photovoltaic groups. To explore further avenues of applications, it is important to understand various properties and the phase transformations of TiO2 polymorphs at ambient conditions. The detailed study on the phase transitions (pressure induced) of the low-pressure polymorphs (rutile, anatase, brookite and columbite) of TiO2 is surprisingly missing in the literature. In view of the above, we have carried out ab-initio calculations on these four polymorphs of TiO2 using full potential linearized augmented plane wave [FP-LAPW] method to study the structural phase transitions and elastic properties. The transition pressures at 0 K among anatase (A), rutile (R), brookite (B) and columbite (C) are found out to be -2.4 GPa (A-B), 5.3 GPa (A-R), 5.7 GPa (A-C), 8.7 GPa (R-C), 10.7 GPa (B-C) and 11.6 GPa (B-R) respectively. The elastic properties at P = 0 GPa are examined through computation of elastic constants for all polymorphs. All the polymorphs are found to be mechanically stable. The anisotropy in shear moduli and directional dependence of Young's modulus are also investigated for all the polymorphs.

Divalent cations mixed lead halide perovskites with enhanced performances, high stabilities, and reduced toxicity are requisite to make persistent progress in perovskite solar cells. However, the mixing strategy is not reported extensively in search of a lead reduced structure. Herein, we report the structural, electronic and optical properties of RbPb 1-x M x I 3 (where, M={Sn,Ge} and x={0.25, 0.50, 0.75}) by alloying the B-site with Sn and Ge, using the density functional theory. The formation enthalpy is estimated for all RbPb 1-x M x I 3 (with x= 0.25, 0.50, 0.75), which confirms stability for all the structures. The energy bandgap and density of states (DOS) have been thoroughly investigated. The energy bandgap decreases with the increasing Sn/Ge contents, the lowest bandgap of 1.850 eV is observed at x = 0.50 in the case of RbPb 1-x Ge x I 3 systems. Further, the effective masses and the binding energy of excitons and spectroscopic limited maximum efficiency (SLME) are also estimated for all the mixed systems. The exciton type is observed to change from Mott-Wannier to Frenkel type with increasing the contents of both Sn and Ge at the B-site. The maximum efficiency of 23% is achieved using an active layer containing an equal admixture of Sn/Ge and Pb. The estimated parameters of both the mixed systems are consistent with the available literature of similar types.