Improving the stability
and tuning the optical properties of semiconducting
perovskites are vital for their applications in advanced optoelectronic
devices. We present a facile synthetic method for hybrid composites
of perovskites and metal–organic frameworks (MOFs). A simple
two-step solution-based method without organic surfactants was employed
to make all-inorganic lead-halide perovskites (CsPbX3;
X = Cl, Br, I, or mixed halide compositions) form directly in the
pores of MIL-101 MOF. That is, a polar organic solution of lead halide
(PbX2) was impregnated into the MOF pores to give PbX2@MIL-101, which was then subjected to a perovskite-formation
reaction with cesium halide (CsX) dissolved in methanol. The compositions
of the halogen anions in the perovskites can be modulated with various
halide precursors, leading to CsPbX3@MIL-101 composites
with X3 = Cl3, Cl2Br, Br2Cl, Br3, Br2I, I2Br, and I3 that exhibit gradual variation of band gap energies and tuned emission
wavelengths from 417 to 698 nm.
We
report the characteristic magnetic behaviors of nonemissive
(N416) and green emissive (G416) Cs4PbBr6 perovskite
crystals. N416 exhibits a diamagnetic behavior, while G416 shows an
additional superparamagnetic behavior, demonstrating the existence
of paramagnetic electron spins in the G416. Although G416 and N416
crystals belong to the same rhombohedra unit cell with zero-dimensional
(0D) connectivity of the [PbBr6]4– octahedron,
the G416 crystal has a smaller unit cell volume than N416. 133Cs magic-angle-spinning NMR spectroscopy demonstrated the presence
of defects in G416 and the extremely low concentration of a CsPbBr3 phase in both crystals. The DFT calculation results for the
defected N416 crystal structure possessing Br vacancies included the
experimentally observed blue shift of the high-energy optical band
in the G416, which reinforces the existence of intrinsic defects in
the G416. Our findings reveal that the unusual green emission and
paramagnetic domains stem from structural defects in the 0D perovskites.
Transparent AgI-CuI heterojunctions with high rectifying diode behavior were prepared via vapor-phase iodization of metal thin films on transparent conducting oxide substrates. At room temperature, Ag and Cu metal thin films were quickly transformed into the transparent and well-crystallized β-phase of AgI and the γ-phase of CuI, respectively. The AgI and CuI films exhibited n-type and p-type semiconductor properties, respectively, with wide band gaps. The heterojunctions were obtained by applying the CuI film to the AgI film in a sequential iodization process. AgI compounds generally have poor air-stability under light, making them suboptimal for use in electronic applications. Here, we used a CuI top layer to inhibit the photodecomposition of the AgI bottom layer, resulting in an air-stable and smooth AgI-CuI film. We also propose a simple patterning method for the AgI-CuI layer using selective decomposition of AgI without the need for lithography equipment or toxic chemicals. Although there is metal ion exchange between the two layers, each layer has a different chemical composition and crystal structure; therefore, the AgI-CuI heterojunction exhibits pn-diode behavior with a rectifying ratio of 9.4 × 10, which is comparable to that of other transparent pn-diodes. These findings open a new path for electronic application of AgI materials.
Hybrid light sensitizer: The exfoliated, layered, double hydroxide nanosheets induced a strong photochromic function in the anthraquinone sulfonate anions that were chemically immobilized on the nanosheets. This hybrid nanosheet was applied to the dye‐sensitized solar cell as a new light sensitizer that was self‐organized on TiO2 spheres, resulting in a higher solar‐to‐electric conversion efficiency than the single‐dye cell, owing to the intense photochromic function of the hybrid nanosheets.
Large‐scale (as much as 200 g in a batch) and surfactant‐free syntheses of the CuInxGa1–xSe2 and the CuInxGa1–xS2 nanoparticles were investigated by employing a sonochemical process under ambient conditions. This synthetic approach eliminates the need for organic stabilizers, which may act as an insulator in the final device, and reduces the number of reaction steps for synthesis of high‐quality CISe nanocrystals. We also demonstrate the solution‐based fabrication of the thin film photovoltaic devices with a conversion efficiency of 2.62 % by using nanocrystal‐based inks. The device was fabricated with 2 μm of a CIGS absorber layer on Mo‐coated soda lime glass, 70 nm of a chemical‐bath‐deposited CdS layer, 100 nm of an intrinsic ZnO layer, followed by 800 nm of a Al‐doped ZnO layer. Finally, a patterned Ag (200 nm) grid was deposited on the top of the device. The current results offer a promising alternative for solution‐based CIGSe thin film solar cells, with a higher efficiency.
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