Solid-State Nanopore Confinement for Band Gap Engineering of Metal-Halide Perovskites

Tuning the band gap of semiconductors via quantum size effects launched a technological revolution in optoelectronics, advancing solar cells, quantum dot light-emitting displays, and solid state lasers. Next generation devices seek to employ low-cost, easily processable semiconductors. A promising class of such materials are metal-halide perovskites, currently propelling research on emerging photovoltaics. Their narrow band emission permits very high colour purity in light-emitting devices and vivid life-like displays paired with low-temperature processing through printing-compatible methods. Success of perovskites in light-emitting devices is conditional upon finding reliable strategies to obtain tunability of the band gap. So far, colour can be tuned chemically by mixed halide stoichiometry, or by synthesis of colloidal particles. Here we introduce a general strategy of controlling shape and size of perovskite nanocrystallites (less than 10 nm) in domains that exhibit strong quantum size effects. Without manipulation of halide stoichiometry, we achieve fine-tuning of band gap across a wide colour gamut from near infrared to ultraviolet through solid-state confinement in nanoporous alumina (npAAO) or silicon (npSi) scaffolds. Confinement in npSi facilitates a ~50 nm hypsochromic shift from green to blue photoluminescence for caesium-bromide perovskite nanocrystals. By infiltrating electrically addressable npAAO templates, we fabricate perovskite nanorod light-emitting diodes achieving blue shifted narrow-band (17 nm full width at half maximum, FWHM) emission. Our device demonstrations corroborate band gap engineering through solid-state confinement as a powerful tool to precisely control the optoelectronic properties of perovskite nanocrystal emitters in next generation solution-derived photonic sources.