Solvent-Free Synthesis and Thin-Film Deposition of Cesium Copper Halides with Bright Blue Photoluminescence

Abstract

Non-toxic alternatives to lead halide perovskites are highly sought after for applications in optoelectronics. Blue-luminescent materials are especially demanded as they could be used to prepare white light-emitting diodes, with important potential applications in lighting systems. However, wide bandgap blue emitters with high photoluminescence quantum yields (PLQY) are typically more difficult to obtain as compared to green-or red-emitting ones. Here, we prepared two series of inorganic cesium copper halides, with the general formulas Cs3Cu2X5 and CsCu2X3 (X = Cl, Br, I, and mixtures thereof) by dry mechanochemical synthesis at room temperature. X-ray diffraction demonstrates quantitative conversion of binary precursors into the desired ternary structures and good halide mixing in single-phase compounds. We identified Cs3Cu2I5 as the most promising material as it maintains blue luminescence centered at 442 nm with high PLQY (>40%) after several days in air (Cs3Cu2Cl5 shows significantly higher PLQY over 80% but is unstable in air). Based on this, we fabricated homogeneous and pinhole-free Cs3Cu2I5 thin films by thermal single-source vacuum deposition. Crystalline phase and photoluminescence are maintained in the thin films, validating that these low-toxicity materials can be synthesized and processed by fully solvent-free routes for a widespread implementation in optoelectronic devices. EXPERIMENTAL SECTIONMaterials. Cesium chloride (CsCl, > 99 %), cesium bromide (CsBr, > 99 %) and cesium iodide (CsI, > 99 %) were purchased from TCI.non-exposed and exposed powders; variation in PLE and PL wavelengths of Cs3Cu2X5 powders; XRD and PL spectra of solution processed thin-films; SEM image of thin-film by SSVD of Cs3Cu2I5.

A Highly Efficient and Stable Blue‐Emitting Cs5Cu3Cl6I2 with a 1D Chain Structure

“…The Rietveld refinement of the powder XRD pattern indicated that Cs 3 Cu 2 Cl 5 adopts space group Cmcm ( a = 15.449[5] Å, b = 8.7562[3] Å, and c = 8.6814[3] Å) (see Tables S8–S10, Supporting Information), which is different from the I and Br analogs ( Pnma ), as shown in Figure 1d,e. [ 21–23 ] For the Cs 3 Cu 2 Cl 5 , each Cu + ion has been coordinated with three Cl − ions and adopted a near‐planar configuration. Through Cl corner sharing, two [CuCl 3 ] 2− units formed an isolated folded dimer [Cu 2 Cl 5 ] 3− with a 75.51° face angle.…”

Near‐Unity Cyan‐Green Emitting Lead‐Free All‐Inorganic Cesium Copper Chloride Phosphors for Full‐Spectrum White Light‐Emitting Diodes

“…Sebastia‐Luna et al successfully synthesized β‐Cs 3 Cu 2 Cl 5 , and found that the structure of β‐Cs 3 Cu 2 Cl 5 metamorph rapidly in the air, which illustrates that the β‐Cs 3 Cu 2 Cl 5 synthesized using the general method was unstable. [ 26 ] According to the structure diagram, [Cu 2 Cl 5 ] 3− chain is the basis of β‐Cs 3 Cu 2 Cl 5 , and Cs + fills in the gaps in the [Cu 2 Cl 5 ] 3− chain, as shown in Figure 2b. Therefore, we infer that the role of hypophosphorous acid is to stabilize [Cu 2 Cl 5 ] 3− skeleton and ensure the stable existence of β‐Cs 3 Cu 2 Cl 5 structure.…”

“…[ 23,24 ] The 1D β‐Cs 3 Cu 2 Cl 5 containing nontoxic and earth‐abundant elements, was reported as a cyan‐green phosphor, but the β‐Cs 3 Cu 2 Cl 5 with high PLQY(>90%) powders usually prepared by complex methods and environmental unfriendly organic solvent were used during their complex synthesis (Table S1, Supporting Information). [ 25–29 ] Although neither Sebastia‐Luna et al and Xie et al did not use any organic solvents, their synthetic samples of PLQY were up to 81%. Therefore, it is necessary to explore a simple and environmental‐friendly synthetic method for large‐scale preparation of β‐Cs 3 Cu 2 Cl 5 .…”

Recent Advances and Perspectives on Powder‐Based Halide Perovskite Film Processing

“…[ 31–33 ] By the addition of appropriate organic molecules, it is possible to synthesize perovskite nanocrystals. [ 34 ] Furthermore, the mechanochemical synthesis of lead‐free perovskites based on tin, [ 16,35,36 ] copper, [ 37 ] or bismuth [ 38 ] on the B position was demonstrated as well. Mechanochemistry is a solvent‐free synthesis method.…”