Incorporation of potassium halides in the mechanosynthesis of inorganic perovskites: feasibility and limitations of ion-replacement and trap passivation

Potassium halides (KX; X = I, Br, or Cl) were incorporated as partial replacements of CsBr in the mechanosynthesis of CsPbBr3. This led to partial substitution of both monovalent ions forming mixed Cs1−xKxPbBr3−yXy perovskites. Longer photoluminescence lifetimes were also observed, possibly linked to the formation of a non-perovskite KPb2X5 passivating layer.


Synthesis
Equimolar AX : PbBr 2 powders (AX = CsBr or CsBr 0.8 KY 0.2 ; where Y = I, Br, or Cl) were mixed inside a nitrogen-filled glovebox.Then, approximately 3 grams of the mixed precursors powders were introduced inside 10 mL zirconia ball-mill jars with 2 zirconia beads of 10 mm in diameter.The jars were closed under nitrogen so that the powders were not exposed to air.Then ball-milling was performed with a MM-400 straight ball-mill from Retsch, at a frequency of 30 Hz for 5 hours.

XRD X-ray diffraction was measured with a Panalytical Empyrean diffractometer equipped with
CuKα anode operated at 45 kV and 30 mA and a Pixel 1D detector in scanning line mode.Single scans were acquired in the 2Θ = 10° to 50° range in Bragg-Brentano geometry in air.Data analysis was performed with HighScore Plus software.

Absorbance and photoluminescence spectroscopy
Absorbance was measured with a High Power UV-VIS fiber light source, integrated sphere and Avantes Starline AVASpec-2048L spectrometer in reflection mode.Photoluminescence was Electronic Supplementary Material (ESI) for RSC Advances.This journal is © The Royal Society of Chemistry 2018 measured with a continuous wave 375 nm diode laser with a 400nm filter, and Hamamatsu PMA 11 spectrometer.For a typical spectrum 10 scans of 1 second were averaged.

Photoluminescence measurements
A third harmonic (355 nm) of a Nd:YAG pulsed laser with 1.1 ns pulse duration, 1 kHz pulse repetition frequency and 20J/cm 2 excitation density was used as an excitation source for the PL measurements.To detect the time-resolved PL kinetics an integrated PL signal was directed through a multimode optical fiber to a time correlated single photon counting electronic board.For the PL spectra measurements, the PL signal was directed through an optical fiber to an Ocean type spectrometer.

Figure S 1 .
Figure S 1. XRD signal of samples prepared from pure CsBr (black line) and partly (20%) substituted by KBr (green line).Selected areas of the diffractograms are shown in Figure 1.Reference pattern for bulk orthorhombic CsPbBr 3 is shown as orange columns.

Figure S 3 .
Figure S 3. XRD signal of samples prepared from pure CsBr (black line) and partly (5%) substituted by KBr (green line).Effects of KBr are qualitatively similar than in the case of 20% (Figure S1 and Figure 1) although to a lesser extent, as may be expected by a lower percentage of KBr.

Figure S 4 .
Figure S 4. Photoluminescence spectra of reference and KBr sample fitted with two gaussian peaks.The KBr sample shows a reduction in the relative intensity of the high-energy component as explained in the main text.