Synthesis and characterization of mixed-halide 0D perovskites via MCS
Precursor salts (CsCl, CsBr, CsI, PbCl2, PbBr2, PbI2, in respect to the desired halide stoichiometric ratio with a fixed total mass of 2.278g) were put in a stainless-steel jar with two-stainless grinding balls (28.65g, 1.9cm diameter) and the jar was shaken with a shaker-type ball mill (Mixer Mill MM-400, Retsch) at 17 Hz for 3 h.
The formation of cesium lead halide 0D perovskite(Cs4PbX6) powder samples with mixed-halide compositions through shaker-type MCS was confirmed with various structural and optical analytical techniques.
Figure 1. (a) Schematic image of the shaker-type ball mill and photographs of the synthesized powder samples with various halide composition. (b) PXRD patterns, (c) 133Cs ssNMR spectra (at 22kHz MAS and 300K), (d) PL spectra and (e) absorption spectra within the visible range (400-750nm) of the mixed-halide 0D perovskite powder samples.
Transferring the powder samples to thin films through flash evaporation
270nm SiO2 on silicon, silicon, and glass substrates were sequentially cleaned with acetone, isopropyl alcohol, and deionized water in a sonicator for 10 min each, then the exposed to O2 plasma using the reactive-ion etching technique (power of 50W, flow of 30cm3/min, and duration of 120 s) to generate hydrophilic surfaces.
The synthesized perovskite powder samples were loaded in a tungsten boat, and the cleaned substrates were placed in a vacuum chamber at a height of 30 cm from the boat.
The chamber was evacuated to 5 X 10-6 Torr, and the tungsten boat was heated by a current of 140 A.
After the deposition, the films were annealed at 150 °C in 1 X 10-4 Torr vacuum for 5 min.
PXRD and PL analysis confirmed the transferability of the 0D perovskite structures of the source powder to the deposited films, and FE-SEM images demonstrate the uniform film surface with a thickness of ~250 nm.
Figure 2. (a) Schematic image of single-source vacuum deposition. (b) HRXRD pattern, (c) PL spectra of the 0D perovskite films. (d) Top view (left) and cross-section view (right) FE-SEM images of the Cs4PbBr6 film. (e) Images for the 0D perovskite films under UV irradiation without adjusting the color.
Characterization
X-ray diffraction (XRD) patterns were measured by Rigaku SmartLab diffractometer. Photoluminescence (PL) spectra were measured by JASCO FP-8500 spectrofluorometer. UV-vis absorption spectra were measured by JASCO V-770 UV-vis spectrophotometer. 133Cs solid-state nuclear magnetic resonance (ssNMR) spectra were measured by 600 MHz Bruker ADVANCE III NMR spectrometer with a spinning speed of 22 kHz at 14.1 T. The field-emission scanning electron microscope (FE-SEM) images were obtained by JEOL JSM-7800F.