Metal halide perovskites have fascinating electronic properties and have already been implemented in various devices. Although the behavior of the properties of lead halide perovskite nanocrystals has been studied, the properties of lead-free perovskite nanocrystals are less wellunderstood because synthesizing them is still very challenging. Here, a simple and popularizable method has been demonstrated to grow monodisperse bismuth-halide double perovskite nanocrystals, Cs 2 AgBiBr 6 (1), inside three kinds of mesoporous silica templates. The size and morphology of nanocrystals depend on the structure and pore size of the template. Structural analysis shows that the nanocrystals of various sizes and morphologies retain the crystal structure of bimetallic perovskite. 1 exhibits different morphologies in the silicon channels of three templates: square nanoparticles in KIT-6, spherical and rodlike particles in SBA-15, and nanowires in MCM-41. UV−vis−NIR and photoluminescence measurements show us the variation of band gap and carrier recombination time due to quantum confinement of nanocrystals in mesoporous silicon materials. The band gaps of nanocrystals in the template exhibit an obvious blue shift compared with that of the bulk sample, and the carrier recombination time is significantly shortened. We show that mesoporous silicon templates can be used to prepare lead-free perovskite nanocrystals, and the controllable preparation of nanocrystals can be achieved by the template's own characteristics. This provides a new idea for us to find new functional materials of lead-free metal halide solidstate light-emitting diodes.
Hybrid halide perovskites are emerging semiconducting materials with a diverse set of remarkable optoelectronic properties. Besides the widely studied lead halide perovskites, Pb-free metal halides such as Bi-and Sb-containing hybrid organic− inorganic materials have shown potential as semiconductors and have been deemed candidates for optoelectronic devices. Here, we report a series of 1D Sb/Bi-based organic−inorganic hybrid alloys: [4ApyH]Sb x Bi 1−x I y Br 4−y , where 4ApyH stands for the 4-aminopyridine cations. These compounds are assembled by edge-sharing octahedral [MX 6 ] units stabilizing 1D chains with organic cations filled in between. The crystallographic data of eight selected complexes show that [4ApyH]Sb x Bi 1−x I y Br 4−y has at least five phases (space group) with the difference metal and halogen content:and [4ApyH]SbBr 4 (100 K)), I2/a ([4ApyH]Sb 0.5 Bi 0.5 I 2 Br 2 and [4ApyH]SbI 2 Br 2 ), and C2/c ([4ApyH]SbI 4 (298 K) and [4ApyH]SbBr 4 (298 K)). Powder X-ray diffraction shows that the phase of the sample changes with a change of the metal and halogen ratios, and the change law accords with Vegard's law. The optical band gaps are heavily affected by the metal and halide contents, ranging from 1.94 eV for [4ApyH]BiI 4 to 2.73 eV for [4ApyH]SbBr 4 . When Sb substitutes for Bi to form an alloy, the band gap increases from 1.94 for [4ApyH]BiI 4 to 1.67 eV for [4ApyH]SbI 4 , from 2.13 eV for [4ApyH]BiI 2 Br 2 to 2.41 eV for [4ApyH]SbI 2 Br 2 , and from 2.55 eV for [4ApyH]BiBr 4 to 2.73 eV for [4ApyH]SbBr 4 . The conductivity of [4ApyH]Sb x Bi 1−x I 4 increased from ∼1.00 × 10 −15 to 2.14 × 10 −8 S cm −1 with an increase of the Sb content. Solution-deposited thin films of the nine complexes show the same (110) orientation, displaying a parallel growth orientation with respect to the substrate. The devices of [4ApyH]Sb 0.8 Bi 0.2 I 4 and [4ApyH]SbI 4 demonstrated stable open-circuit photovoltages of 0.55 and 0.44 V, steady-state short-circuit photocurrent densities of 1.52 and 1.81 mA cm −2 , and light-to-electrical energy conversion efficiencies of 0.29% and 0.30%, respectively.
A dimensional conversion process of semiconducting lead bromide perovskites is followed by electrospray ionization mass spectrometry (ESI-MS), powder X-ray diffraction (PXRD), microcalorimetry and crystallography.
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