Colloidal Synthesis and Optical Properties of Perovskite-Inspired Cesium Zirconium Halide Nanocrystals

Abstract

Optoelectronic devices based on lead halide perovskites are processed in facile ways, yet are remarkably efficient. There are extensive research efforts investigating lead-free perovskite and perovskite-related compounds, yet there are challenges to synthesize these materials in forms that can be directly integrated into thin film devices rather than as bulk powders. Here, we report on the colloidal synthesis and characterization of lead-free, antifluorite Cs 2 ZrX 6 (X = Cl, Br) nanocrystals that are readily processed into thin films. We use transmission electron microscopy and powder X-ray diffraction measurements to determine their size and structural properties, and solid-state nuclear magnetic resonance measurements reveal the presence of oleate ligand, together with a disordered distribution of Cs surface sites. Density functional theory calculations reveal the band structure and fundamental band gaps of 5.06 and 3.91 eV for Cs 2 ZrCl 6 and Cs 2 ZrBr 6 , respectively, consistent with experimental values. Finally, we demonstrate that the Cs 2 ZrCl 6 and Cs 2 ZrBr 6 nanocrystal thin films exhibit tunable, broad white photoluminescence with quantum yields of 45% for the latter, with respective peaks in the blue and green spectral regions and mixed systems exhibiting properties between them. Our work represents a critical step toward the application of lead-free Cs 2 ZrX 6 nanocrystal thin films into next-generation light-emitting applications.

Vacancy‐Ordered Double Perovskite Rb2ZrCl6−xBrx: Facile Synthesis and Insight into Efficient Intrinsic Self‐Trapped Emission

“…(The specific details are discussed in the calculation section) Therefore, here we can obtain the highest PLQY equal 90.2%, which act the best value among the vacancy-ordered double perovskites. [31,45,75,76] Atomic substitution is a primary method for semiconductor bandgap engineering, [81] here, we adopt halogen anion substitution to synthesize a series of mixed halide MCs (Rb 2 ZrCl 6−x Br x , x = 0, 0.5, 1, 1.5, 2). (Details in Synthesis section of the Supporting Information) XRD patterns indicate that all the MCs www.advopticalmat.de exhibit a pure cubic phase retaining the original host structure of Rb 2 ZrCl 6 (Figure 3a).…”

“…(The specific details are discussed in the calculation section) Therefore, here we can obtain the highest PLQY equal 90.2%, which act the best value among the vacancy‐ordered double perovskites. [ 31,45,75,76 ]…”

“…For example, solvent-thermal method was adopted to fabricate Cs 2 ZrCl 6 (need 180 °C for 10 h), [31] and Cs 2 ZrX 6 (X = Cl, Br) nanocrystals were also got by using strict air-free Schlenk line technique. [45] Cs 2 TeI 6 film was fabricated by employing antisolvent method under a nitrogen atmosphere with controlled levels of H 2 O (<5 ppm). [46] Cs 2 SnI 6 nanocrystals were synthesized via hot-injection process at high temperature of 220 °C.…”

Interfaces in metal halide perovskites probed by solid-state NMR spectroscopy

“…Solid-state DNP SENS has also been used to study the core and surface of MHP-inspired Cs 2 ZrCl 6 NCs, including the composition of the surface ligands and exposed atomic sites. 386 Such atomic-level insights into the MHP NC interfaces, precipitated solids or dispersed colloids, may enable rational design of new ligands and provide opportunities to develop molecular passivation strategies. SsNMR studies of colloidal MHP NCs can build on the literature of solution-state NMR studies of dispersed MHP colloids.…”

Colloidal synthesis of lead-free Cs2TiBr6−xIxperovskite nanocrystals

“…They have general formula A2BX6, which is obtained by the removal of half the B +2 cations in the archetypical ABX3 perovskite structure, and the use of tetravalent cations instead in order to balance the charges (see Scheme 1). Over the last 5 years, vacancy-ordered perovskites containing tin 18,19 , palladium 20 , tellurium 21 , zirconium 22 and titanium 23,24 have been synthesized and characterized. Among them, cesium titanium halide perovskite stands out as promising candidate for lead-free perovskite solar cells in view of its favorable bandgap for solar cell applications.…”