First principles DFT analysis of lead free rb2minx6 double perovskite halides for photovoltaic applications

Abstract

Perovskites have emerged as a new superstar in the field of photovoltaics. This group of semiconductors has a wide range of properties that are suitable to be used in a wide range of optoelectronic. The efficiency of perovskite solar cells has greatly increased during the past ten years, and the organic-inorganic hybrid halide perovskite foramidinium lead tri-iodide (FAPbI3) has attained a high efficiency of 25.8%. Commercial use of halide perovskites may revolutionize the field of world photovoltaic and energy due to having cheaper, easily available in nature, easy, rapid and low temperature processing, and more efficient than silicon-based technology. But toxicity and insufficient long-term stability are the main barriers to being used commercially in large-scale applications. Finding stable, non-toxic, Pb-free perovskites is therefore crucial for the advancement of perovskites-based optoelectronic technologies. Recent studies demonstrated that the stability and toxicity issues can be solved simultaneously by using lead-free, all-inorganic double halide perovskites. This thesis presents a first-principles Density Functional Theory (DFT) investigations of the structural, electronic, optical and mechanical properties and thermodynamic and mechanical stability of Alkaline and Indium based noble inorganic double halide perovskites group Rb2MInX6 (where, M= Li, Na and K and X= Cl, Br, I). It is found from this study that Rb2LiInX6 perovskites have failed to meet the structural stability criterion imposed by the octahedral factor. First principles study demonstrates that Rb2KInX6 have structural, and thermodynamical stability against decomposition but don’t have mechanical stability. On the other hand, all the Sodium (Na) based perovskites, Rb2NaInX6, have structural, mechanical, and thermodynamical stability against decomposition and show ductile behavior and direct nature in the band gap (3.01 eV for Rb2NaInCl6 1.81 eV for Rb2NaInBr6 and 0.66 eV for Rb2NaInI6). Rb2NaInBr6 and Rb2NaInI6 have strong absorption in the visible range and suitable band gap and electron-effective mass for use in solar cells. Additionally, we have found that Rb2NaInCl6 exhibits strong UV absorption and suitable VBM and CBM energy to function as a photocatalyst in the water-splitting process.