Discoveries of halide-based and halide-free perovskite compounds have been given birth to a significant variety of scientific interest in the last 5 years. [1] These can be evident of the variety of research topics that have often been appeared in thousands of peer-reviewed international journals. [2] These can be easily traceable if the term "perovskite" would be searched on the internet in combination with other keywords such as organometal, organohalide, organometallic, hydrogen bonding, octahedral tilting, diffusion length, vacancies, tandem, charge and polaron transport, ion migration, defect tolerance, exciton binding energy, slow electron-hole recombination, low bandgap material, indirect-to-direct bandgap transition, photoluminescent and vibrational spectra, dielectric constant, photo-generated effective carrier masses, density of states spectra, ferroelectrics, hysteresis, X-ray diffraction, neutron diffraction, Rashba splitting and rotational disorder, among several others. This is obviously owing to the mysterious importance of these ultra-soft nanomaterials in the area of photovoltaics, especially to design and develop the third generation (perovskite) solar cell technology. [3] Some of these materials (e.g., CH₃NH₃PbI₃) have been certified to have solar power conversion efficiencies that can be tuned up to 22%, [4] and have warranted environmental stability up to 1 year. [5] In any case, and in this presentation, I am aiming to uncover the implication of a broad range of noncovalent interactions especially the hydrogen-, halogen- and other sigma-hole inspired bonding interactions [6] that are useful for the design of hybrid organic-inorganic and all-inorganic perovskite materials. As such, the various results that have been presented in the literature by diverse research groups on lead-free and -based perovskite compounds will be briefly outlined, together with some of our own computational results on various newly discovered BMY₃ type perovskites, where B = organic/inorganic monovalent cation (CH³NH³⁺ /Cs⁺), M = divalent metal cation (Pb²⁺ /Sn²⁺), and Y = monovalent halide anion (Y = F, Cl, Br, I).

References
[1] J. Bisquert, J. Phys. Chem. Lett. 2016, 7, 775.
[2] P. R. Varadwaj, Helv. Chim. Acta 2017, 100, e1700090.
[3] J. Yana, B. R. Saunders, RSC Adv. 2014,4, 43286.
[4] National Renewable Energy Laboratory (NREL) Best Research-Cell Efficiency chart.
https://www.nrel.gov/pv/assets/images/efficiency-chart.png (accessed on September 29,
2017).
[5] G. Grancini, et al., Nat. Commun. 2017, 8, 15684.
[6] A. Varadwaj, P. R. Varadwaj, K. Yamashita, J. Comput. Chem. 2017,
DOI:10.1002/jcc.25073.