Highly efficient CsPbBr3@glass@polyurethane composite film as flexible liquid crystal display backlight

Inorganic lead halide perovskite quantum dots (CsPbX3 QDs (X = Cl, Br, or I)) have attracted more and more attention due to their high absorption coefficient, narrow emission band, high quantum efficiency, and tunable emission wavelength. However, CsPbX3 QDs are decomposed when exposed to bright light, heat, moisture, etc., which leads to severe luminous attenuation and limits their commercial application. In this paper, CsPbBr3@glass materials were successfully synthesized by a one-step self-crystallization method, including melting, quenching and heat treatment processes. The stability of CsPbBr3 QDs was improved by embedding CsPbBr3 QDs into zinc-borosilicate glass. Then, the CsPbBr3@glass was combined with polyurethane (PU) to form a flexible composite luminescent film CsPbBr3@glass@PU. This strategy enables the transformation of rigid perovskite quantum dot glass into flexible luminescent film materials and further improves the photoluminescence quantum yield (PLQY) from 50.5% to 70.2%. The flexible film has good tensile properties, and its length can be strained 5 times as long as the original length. Finally, a white LED was encapsulated by combining CsPbBr3@glass@PU film and red phosphor K2SiF6:Mn4+ with a blue LED chip. The good performance of the obtained CsPbBr3@glass@PU film indicates that it has potential application in flexible liquid crystal displays (LCDs) as a backlight source.

In Situ Growth of High-Quality CsPbBr3 Quantum Dots with Unusual Morphology inside a Transparent Glass with a Heterogeneous Crystallization Environment for Wide Gamut Displays

All-inorganic CsPbBr₃ perovskite quantum dots (QDs) are considered to be one of the most promising green candidates for the new-generation backlight displays. The pending barriers to their applications, however, lie in their mismatching of the target window of green light, scalable production, susceptibility to the leaching of lead ions, and instability in harsh environments (such as moisture, light, and heat). Herein, high-quality CsPbBr₃ QDs with globoid shapes and cuboid shapes were in situ crystallized/grown inside a well-designed glass to produce nanocomposites with peak emission at 526 nm, which not only exhibited photoluminescence quantum yields of 53 and 86% upon 455 and 365 nm excitation, respectively, but also have been imparted of high stability when they were submerged in water and exposed to heat and light. These characteristics, along with their lead self-sequestration capability and easy-to-scale preparation, can enable breakthrough applications for CsPbBr₃ QDs in the field of wide color gamut backlit display. A high-performance backlight white LEDs was fabricated using the CsPbBr₃ QDs@glass powder and K₂SiF₆:Mn⁴⁺ red phosphor, which shows a color gamut of ∼126% of the NTSC or 94% of the Rec. 2020 standards.

Mid-Infrared Luminescence of the High Stability Perovskite CsPb1-xErxBr3-ZrF4-BaF2-LaF3-AlF3-NaF Fluoride Glass

Perovskites have been studied because of their adjustable wavelength range, high color purity, and wide color gamut. However, they still face some problems such as poor stability and insufficient infrared luminescence. The perovskite glass can improve the stability and luminescence properties of the perovskite. In this paper, a highly stable CsPb_1-xEr_xBr₃-ZBLAN fluoride glass with mid-infrared and visible light emission was prepared. The ZBLAN fluoride glass has good inertness, which can improve the stability of the CsPb_1-xEr_xBr₃ perovskite. The CsPb_1-xEr_xBr₃-ZBLAN fluoride glass can prevent the perovskite from being destroyed by water, oxygen, and laser. The Er³⁺ replaces Pb²⁺ to bond with Br^- to become the luminescent center of the CsPb_1-xEr_xBr₃-ZBLAN perovskite glass, which extends the luminescence to the mid-infrared region. In addition, its luminescent intensity is significantly higher than those of the ZBLAN-Er glass and CsPb_1-xEr_xBr₃ perovskite. After irradiation with a 365 nm UV lamp for 13 h, the luminescence intensity of the CsPb_1-xEr_xBr₃-ZBLAN perovskite glass decreases only by 10%. The EDS spectrum shows that the elements of the CsPb_1-xEr_xBr₃ perovskite are uniformly distributed in the glass matrix. The X-ray diffraction spectrum shows that the sample has both the CsPb_1-xEr_xBr₃ perovskite phase and the glass phase. This indicates that CsPb_1-xEr_xBr₃ is well crystallized in the ZBLAN glass matrix. The three parameters calculated by the Judd-Ofelt theory show that the CsPb_1-xEr_xBr₃ perovskite can increase the covalency and asymmetry around the rare earth ion Er³⁺. The transmission electron microscope can clearly see the morphological structure of the CsPb_1-xEr_xBr₃ perovskite in the ZBLAN glass matrix. The infrared Fourier transform spectroscopy shows that the sample has lower phonon energy. This proves that the sample has good infrared luminescence characteristics. Finally, the visible and infrared light sources were prepared. Under the irradiation of the 365 nm ultraviolet lamp and 980 nm laser, the perovskite glass produces green light and infrared emission.

Exploring the Effect of Electron Withdrawing Groups on Optoelectronic Properties of Pyrazole Derivatives as Efficient Donor and Acceptor Materials for Photovoltaic Devices

Multifunctional pyrazole derivative, i.e. 3-amino-1-(5-hydroxy-3-methyl-1H-pyrazol-4-yl)-1H-benzo[f]chromene-2-carbonitrile (PBCC) has been synthesized and characterized. To shed light on various properties of interests, the ground state geometry was optimized by adopting Density Functional Theory (PBE/TZ2P). The effect of different functionals on the absorption wavelengths was studied by using Time-Domain DFT (TDDFT), e.g. GGA functional PBE, hybrid functionals B3LYP and PBE0, rang separated functionals CAM-B3LYP, LCY-PBE and CAMY-B3LYP, Dispersion Corrections PBE-D3 and B3LYP-D3. Among all these functionals PBE and PBE-D3 were found to be good choices which reproduced the absorption spectra of the PBCC. With the aim to enhance the electro-optical, charge transfer and photovoltaic properties, five new derivatives were designed by di-substituting the –F, –Cl, –Br, –COOH and –CN at benzochromene moiety. The electron injection barrier, band gap alignment and related calculated photovoltaic parameters revealed that PBCC and its newly designed derivatives would be proficient to be used in photovoltaic devices. These compounds can be used as donor materials in dye-sensitized solar cells (DSSCs) with favorable type-II band alignment. Moreover, PBCC and most of its derivatives might also be good choice as efficient acceptors with poly(dithieno[3,2-b:2,3-d]pyrrole thiophene) (PDTPr-T) and donor materials with Phenyl-C61-butyric acid methyl ester (PC61BM) in organic solar cells.