Picoperovskites: the Smallest Conceivable Isolated Halide Perovskite Structures Formed Within Carbon Nanotubes.

Halide perovskite structures are revolutionising the design of optoelectronic materials, including solar cells, light emitting diodes and photovoltaics when formed at the quantum scale. We report four isolated sub-nm, or pico-scale, halide perovskite structures formed inside ∼1.2-1.6 nm single walled carbon nanotubes (SWCNTs) by melt insertion from CsPbBr 3 and lead-free CsSnI 3 . Three directly relate to the ABX 3 perovskite archetype while a fourth is a perovskite-like lamellar structure with alternating Cs 4 and polyhedral Sn 4 I x layers. In ∼1.4 nm diameter SWCNTs, CsPbBr 3 forms Cs 3 Pb II Br 5 nanowires one ABX 3 unit cell in cross section with the Pb 2+ oxidation state maintained by ordered Cs + vacancies. Within ∼1.2 nm diameter SWCNTs, CsPbBr 3 and CsSnI 3 form inorganic polymer-like bilayer structures 1/4 an ABX 3 unit cell in cross-section with systematically reproduced ABX 3 stoichiometry. Producing these smallest halide perovskite structures at their absolute synthetic cross-sectional limit enables quantum confinement effects with first-principles calculations demonstrating band gap widening compared to corresponding bulk structural forms. This article is protected by copyright. All rights reserved.