Structural, electronic and optical properties of lead free Rb based triiodide for photovoltaic application: an ab initio study

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.

First-Principles Investigation of Novel Alkali-Based Lead-Free Halide Perovskites for Advanced Optoelectronic Applications

“…Our predicted R (0) value for RbSnI 3 is reasonably close to Nyayban et al’s estimate of 0.163. 33 For KSnI 3 , RbSnI 3 , and CsSnI 3 , the highest reflectivity R (ω) values are 0.59, 0.59, and 0.52 correspondingly. These high reflectivity R (ω) values show a better indication for their usage as a coating material that reduces reflection.…”

“…According to Figure a, the detected static values ε 1 (0) for the three materials (Table ) are 5.6, 5.4, and 7.9, respectively. Our estimated ε 1 (0) for RbSnI 3 was found to agree with the value reported in the literature, which was estimated to be around 5.45 by Nyayban et al According to Figure b, KSnI 3 , RbSnI 3 , and CsSnI 3 have high peak points in the imaginary component at about 3.0, 3.0, and 1.5 eV, respectively. Results demonstrate that, when compared to the other two compounds, KSnI 3 has the highest polarizability at around 3.0 eV, whose value is around 10.2.…”

“…The static reflectivity R (ω) for these three halide perovskites is shown in Figure a, with values for KSnI 3 , RbSnI 3 , and CsSnI 3 being about 0.16, 0.17, and 0.23, respectively (see Table ). Our predicted R (0) value for RbSnI 3 is reasonably close to Nyayban et al’s estimate of 0.163 . For KSnI 3 , RbSnI 3 , and CsSnI 3 , the highest reflectivity R (ω) values are 0.59, 0.59, and 0.52 correspondingly.…”

“…When compared with similar inorganic perovskite halide materials, the CsPbI 3 demonstrates higher photovoltaic performance. , Even yet, the CsPbI 3 undergoes a nonperovskite transformation at ambient temperature that results in a structure that has a band gap of 2.83 eV and a negligible photovoltaic effect. As compared to earlier organic and inorganic hybrid perovskites, switching Rb to Cs is predicted to boost the device’s reliability. − This material is preferable to other solid-state systems in electrolytes having TiO 2 for dye-sensitized Gratzel solar cell materials because it has high mobility power in addition to CsSnI 3 . The well-organized solar radiation absorption constituents in this kind of perovskite comprise mixed halide perovskites made of cesium (Cs) and tin (Sn). , Contrary to most semiconducting materials, the intriguing features of CsSnI 3 are linear with a considerable rise in bandgap energy ( E g ) along with an increasing temperature .…”

Ab-initio study of the effect of bromide mixing into RbPbI$_3$ on the structural, electronic and optical properties

“…Perdew-Burke-Ernzerhof (PBE) [39] exchange correlation functional has been reported [40][41][42][43] to estimate the bandgap accurately for the halide perovskites without considering the spin orbit coupling (SOC) effect. Again PBE including SOC are reported [44] to underestimate the bandgap but does not alter the pattern of the bandstructure. Additionally the hybrid functional is also reported [45] to overestimate the bandgap whereas less computationally demanding TB-mBJ (Tran Blaha modified Becke Johnson) [46] potential is found to estimate the bandgap more accurately [47,48].…”