Bulk Assembly of Zero-Dimensional Organic Lead Bromide Hybrid with Efficient Blue Emission

Zero-dimensional
(0D) organic metal halide hybrids are an emerging
class of light emitting materials with exceptional photoluminescence
quantum efficiencies (PLQEs), thanks to their perfect “host–guest”
structures with light emitting metal halide species periodically “embedded”
in a wide band gap organic cationic matrix through ionic bonds. However,
achieving efficient blue emissions is challenging for this class of
materials, as structural distortions of metal halides often lead to
large Stokes shifts. Here we report a highly luminescent blue emitting
0D organic lead bromide, (C13H19N4)2PbBr4, with a peak emission of 460 nm (2.70
eV), a full width at half maximum (FWHM) of 66 nm (0.40 eV), a Stokes
shift of 111 nm (0.85 eV), and a PLQE of ∼40%. Single crystal
structure analysis shows that individual PbBr42– species adopt a near-seesaw structure, which are coordinated to
benzyl-hexamethylenetetrammonium (C13H19N4+) organic cations. The relatively small Stokes
shift as compared to those of previously reported 0D organic metal
halide hybrids are attributed to the low chemical reactivity of Pb
6s2 lone pairs and the rigid organic cationic matrix. (C13H19N4)2PbBr4 also
shows exceptional stability in air with little-to-no change of properties
for more than a year in ambient conditions.