Two-dimensional
(2D) perovskites have emerged as potential single-source
white-light emitters in solid-state lighting. However, the quantum
yields (PLQY) remain modest, probably ascribed to the limitation of
octahedral distortion modulation. Herein, it is demonstrated that
the PLQY of 2D lead bromide perovskites can be further enhanced to
12.8% if they contain a bulk and optically active conjugated ditertiary
ammonium cation N,N,N′,N′-tetramethyl-1,4-phenylenediammonium
(TMPDA). The pristine alkyl ditertiary ammonium cation N,N,N′,N′-tetramethyl-1,6-hexanediammonium (TMHDA) can only form a
1D lead bromide perovskite with much inferior emission. The robust
emission derives from the ultrahigh octahedral distortions associated
with self-trapped excitons in 2D TMPDAPbBr4. Our experimental
and theoretical results further suggest that the efficient broad-band
emission in 2D TMPDAPbBr4 probably involves Förster
resonant energy transfer where the optically active organic TMPDA2+ acts as a donor and the inorganic PbBr6 slab
acts as an acceptor. Moreover, a 2D perovskite based on the conjugated
ligand exhibits superior electrical properties compared to a 1D perovskite
templated by an alkyl ligand. This work highlights the importance
of molecular engineering to enhance the broad-band emission efficiency
of 2D perovskites.
2D pentamethylenediammonium lead bromide single crystal with distinctive smooth and continuous morphology and decreased interlayer distance exhibits promising photoconductivity performance.
Two-dimensional
(2D) perovskite broadband emitters are gaining
intensive attention in light-emitting fields. However, the limitation
of structure distortion modulation hinders the increase of emission
intensity, and the high toxicity of organic diamine causes potential
damage to human health. Herein, we utilize a green organic spacer
5-ammonium valeric acid (Ava) to template novel 2D lead chloride hybrids,
Ava2PbCl4, where intermolecular O1···H–O2
interactions form between the adjacent organic cation layers. The
intermolecular hydrogen bonding in Ava2PbCl4 causes a larger cation penetration depth which enables larger structural
deformation than the pentamethylenediammonium lead chloride (PDAPbCl4) reference. This octahedral deformation further leads to
ultrabroadband emission in Ava2PbCl4, which
achieves enhanced photoluminescence quantum yield (2.83%) compared
to PDAPbCl4 (0.4%). Further mechanism investigation indicates
that these broadband emissions could be assigned as the transient
self-trapped excitons luminescence. Density functional theory calculation
indicates that the octahedral distortions are traced to an electronic
origin as well. The above findings reveal the key role of intermolecular
hydrogen bonding in modulating the photophysical properties of 2D
perovskites and will benefit the design of green perovskites for optoelectronic
applications.
Hybrid bismuth halides perovskites have emerged as promising candidates for X‐ray detection, due to the strong absorptivity of high‐energy X‐ray photons, high resistivity, large carrier diffusion length and low toxicity. However, the mostly investigated hybrid bismuth iodides single crystals are usually opaque and require a harsh synthesis process. Herein, novel one‐dimensional (1D) pentamethylenediamine bismuth bromide (PDA)BiBr5 single crystals were synthesized via an antisolvent‐assisted crystallization method at room temperature. Bulk (PDA)BiBr5 single crystals have sizes of 10×1.3×1.5 mm3 and high transparency. They are shown to have low density of defects of 2.0×1010 cm−3 and obvious photoconductivity. Moreover, they exhibit large bulk resistivity of 2.13×1011 Ω cm and good X‐ray attenuation coefficient. Consequently, the vertical structured (PDA)BiBr5 single crystal X‐ray photoconductor produces a sensitivity of 3.8 μC Gyair−1 cm−2. This study provides a facile strategy for synthesizing bulk hybrid bismuth bromides single crystals with potential X‐ray detection application.
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