DOI: 10.5061/dryad.qnk98sfv0
title: Two-step spin-coating of vacancy-ordered double perovskites enables growth of thin films for electronic devices

description: Vacancy-ordered double perovskites (VODPs), such as Cs2TeX6 (X = Cl, Br,
 I), are lead-free alternatives to conventional metal-halide perovskites
 (MHPs). One limitation of VODPs is the lack of processes to form thin
 films relevant for physical characterization and electronic devices. A
 two-step spin-coating method was developed for synthesizing high-quality
 films of Cs2TeBr6. Independently depositing CsBr and TeBr4 enables high
 precursor concentration and control over crystallization dynamics. By
 optimizing spin-coating parameters, conversion of precursors to phase pure
 films was observed using structural and surface characterization methods.
 The growth of mixed-halide systems was investigated using alternative
 salts including CsCl and CsI. Formation of halide alloys was found to
 depend on the existence of routes to byproducts. Lastly, single carrier
 diodes of Cs2TeBr6 were designed following valence band characterization
 with photoelectron spectroscopy. Temperature-dependent
 space-charge-limited current measurements revealed that transport occurs
 by hopping and the hole mobility is 3.2 x 10-5 cm2 V-1 s-1 near room
 temperature. The insights from the 2-step procedure provide a pathway
 towards making semiconducting devices from VODPs.
description: Powder X-Ray Diffraction Powder X-ray
 diffraction patterns were collected with a Panalytical Empyrean Powder
 Diffractometer in reflection mode. Cu Kα1 was used as the X-ray radiation
 source with an accelerating voltage of 45 kV and beam current of 40 mA.
 Scans were performed from 2θ =  3° to 2θ = 60° with a step size of 0.04°
 and step time of 40 ms. UV-Vis A
 Shimadzu UV3600 UV-Vis-NIR Spectrometer was used to collect diffuse
 reflectance spectra. Scans were performed from 300 to 900 nm with a step
 size of 0.5 nm. Reflectance data was converted to absorbance with the
 Kubelka-Munk transform. Tauc plots for indirect band gap materials were
 generated to determine the band gap with a linear fit of the absorption
 edge. Photoluminescence Emission
 spectra was collected in reflectance mode with a 430 nm long pass filter,
 spectrometer, and visible CCD detector. Samples were excited at 405 nm
 with a continuous wave laser diode.   Grazing
 incidence wide-angle X-ray scattering (GIWAXS) GIWAXS
 experiments were performed at Stanford Synchrotron Radiation Lightsource
 (SSRL) on beam line 11-3, which has a fixed energy of 12.7 keV and is
 equipped with a two-dimensional Rayonix MX225 CCD area detector. Lanthanum
 hexaboride (LaB6) was used to refine the beam center and
 sample-to-detector distance. Data was collected with an incidence angle of
 3° to access a large range in q. Geometric corrections to the raw images
 were made using Nika. Data was azimuthally integrated with
 WAXStools. Scanning Electron Microscopy
 (SEM) SEM images were collected with a Thermo
 Scientific Apreo C LoVac SEM. Films were mounted onto SEM stubs with
 double-sided copper tape and imaged with accelerating voltages of 5.00 kV
 and beam currents of 0.40 nA. Ultraviolet and X-ray
 Photoelectron Spectroscopy Ultraviolet photoelectron
 spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) experiments
 were performed with a Thermo Scientific ESCALAB Xi+ XPS Microprobe. For
 UPS experiments, before film casting, 20 nm of chromium followed by 90 nm
 of gold were deposited by thermal evaporation onto quartz substrates so
 that films did not experience charging.  Cs2TeBr6 films were cast with an
 initial TeBr4 layer spun at 8000 rpm so that the film was sufficiently
 thin to prevent charging issues. Nickel tape was adhered to the surface of
 the film and wrapped around the edge of the substrate to further assist
 with charge dissipation. A helium I radiation source was used, performing
 5 scans with a pass energy of 1.5 eV, dwell time of 150 ms, and energy
 step size of 0.05 eV. Additional low energy scans were conducted with
 electron charge compensation to ensure that sample charging didn't
 alter the onset, aligning with data collected without compensation. A
 corrected helium I satellite line background was subtracted using CasaXPS.
 For XPS experiments, X-rays are generated with a monochromated aluminum
 anode (1486.7 eV). Scans were performed with a pass energy of 100 eV,
 dwell time of 20 ms, and energy step size of 0.5 eV. Charge compensation
 was applied, and charge shift was accounted for by calibrating to trace
 oxygen photoemission at 531 eV. Thermo Scientific Avantage Data System was
 used to fit peaks with a Smart background and quantify atomic
 percentages. Device Fabrication and Testing
 Devices were tested with a LakeShore Cryogenic Vacuum Probe
 Station and Keithley 2400 SourceMeter. Current-voltage scans were
 performed with a step size of 0.05 V.
description: # Two-step spin-coating of vacancy-ordered double perovskites enables
 growth of thin films for electronic devices Dataset DOI:
 [10.5061/dryad.qnk98sfv0](10.5061/dryad.qnk98sfv0) Cs₂TeBr₆ films were
 characterized with a variety of techniques. Powder X-ray diffraction
 (PXRD) was performed with a Panalytical Empyrean Powder Diffractometer to
 confirm phase purity. Grazing incidence wide-angle X-ray scattering
 (GIWAXS) was conducted at the Stanford Synchrotron Radiation Lightsource
 (SSRL) on beamline 11-3 to assess phase purity and film crystallinity.
 Optical properties were evaluated using a Shimadzu UV3600 UV-Vis-NIR
 Spectrometer for diffuse reflectance and band gap determination, and
 photoluminescence spectra were collected with a spectrometer and visible
 CCD detector under 405 nm laser excitation. Film morphology was examined
 using a Thermo Scientific Apreo C LoVac scanning electron microscope
 (SEM). Ultraviolet photoelectron spectroscopy (UPS) and X-ray
 photoelectron spectroscopy (XPS) were performed on a Thermo Scientific
 ESCALAB Xi+ XPS Microprobe to probe electronic structure and surface
 composition. Device performance was evaluated with current-voltage (J–V)
 measurements using a LakeShore Cryogenic Probe Station and a Keithley 2400
 SourceMeter. ## Cs2TeBr6_Paper_Data.zip – Files and Folders ### Figure 2
 *SEM images of TeBr4 and Cs2TeBr6 films made via two-step spin-coating
 procedure and drop-casting. The drop-cast film was made by dropping 200 μL
 of 0.125 M Cs2TeBr6 solution onto a quartz substrate at 170 °C. 50 μL of
 toluene was deposited in tandem as an anti-solvent. The two-step
 spin-coated film was made by spinning 50 μL of 1 M TeBr4 at 2000 rpm
 followed by 50 μL of 1 M CsBr deposited dynamically at 2000 rpm. PXRD
 patterns for the spin-coated Cs2TeBr6 film and the drop-cast Cs2TeBr6
 film.* "Cs2TeBr6 Dropcast – PXRD.csv" * Measurement conditions
 of PXRD experiment * *2θ* angle (°) and intensity raw data "Cs2TeBr6
 Dropcast – SEM.tif" * Raw TIFF file of SEM image "Cs2TeBr6
 Spincoat – PXRD.csv" * Measurement conditions of PXRD experiment *
 *2θ* angle (°) and intensity raw data "Cs2TeBr6 Spincoat –
 SEM.tif" "TeBr4 Spincoat – SEM.tif" * Raw TIFF files of SEM
 images ### Figure 3 *Azimuthally integrated GIWAXS data collected at a 3°
 incidence angle of Cs2TeBr6 films made by depositing 0.5 M, 1 M, and 1.5 M
 CsBr solution in two-step spin-coating procedure. The TeBr4 pattern is
 included for peak assignment. SEM images of Cs2TeBr6films made with
 varying CsBr deposition spin-speeds.* "0.5 M CsBr Detector Image –
 GIWAXS.tif" * Raw TIFF file of GIWAXS detector image "0.5 M CsBr
 Integrated Signal – GIWAXS.csv" * GIWAXS data after making geometric
 corrections with Nika and integrating with WAXStools * *q* (A⁻¹) and
 integrated intensity data "1 M CsBr Detector Image – GIWAXS.tif"
 * Raw TIFF file of GIWAXS detector image "1 M CsBr Integrated Signal
 – GIWAXS.csv" * GIWAXS data after making geometric corrections with
 Nika and integrating with WAXStools * *q* (A⁻¹) and integrated intensity
 data "1.5 M CsBr Detector Image – GIWAXS.tif" * Raw TIFF file of
 GIWAXS detector image "1.5 M CsBr Integrated Signal –
 GIWAXS.csv" * GIWAXS data after making geometric corrections with
 Nika and integrating with WAXStools * *q* (A⁻¹) and integrated intensity
 data "2000 rpm Second Layer – SEM.tif" "4000 rpm Second
 Layer – SEM.csv" "6000 rpm Second Layer – SEM.csv"
 "8000 rpm Second Layer – SEM.csv" * Raw TIFF files of SEM images
 "TeBr4 Detector Image – GIWAXS.tif" * Raw TIFF file of GIWAXS
 detector image "TeBr4 Integrated Signal – GIWAXS.csv" * GIWAXS
 data after making geometric corrections with Nika and integrating with
 WAXStools * *q* (A⁻¹) and integrated intensity data ### Figure 4 *UV-Vis
 reflectance data for films made by depositing CsCl and CsI solutions of
 varying concentrations. Azimuthally integrated GIWAXS data of films made
 with increasing CsCl concentration. Azimuthally integrated GIWAXS data of
 films made with increasing CsI concentration. Photoluminescence of films
 made with increasing CsI concentration, excited at 405 nm.* "0.5 M
 CsCl – UV-Vis.csv" "1 M CsCl – UV-Vis.csv" "1.5 M CsCl
 – UV-Vis.csv" * Wavelength (nm) and reflectance % raw data "0.5
 M CsCl – PL.csv" "1 M CsCl – PL.csv" "1.5 M CsCl –
 PL.csv" * Wavelength (nm) and emission intensity "0.5 M CsCl
 Integrated Signal – GIWAXS.csv" "0.5 M CsI Integrated Signal –
 GIWAXS.csv" "1 M CsCl Integrated Signal – GIWAXS.csv"
 "1 M CsI Integrated Signal – GIWAXS.csv" "1.5 M CsCl
 Integrated Signal – GIWAXS.csv" "1.5 M CsI Integrated Signal –
 GIWAXS.csv" "0.5 M CsCl Detector Image – GIWAXS.csv" *
 GIWAXS data after making geometric corrections with Nika and integrating
 with WAXStools * *q* (A⁻¹) and integrated intensity data "0.5 M CsI
 Detector Image – GIWAXS.tif" "1 M CsCl Detector Image –
 GIWAXS.tif" "1 M CsI Detector Image – GIWAXS.tif" "1.5
 M CsCl Detector Image – GIWAXS.tif" "1.5 M CsI Detector Image –
 GIWAXS.tif" * Raw TIFF files of GIWAXS detector images ### Figure 5
 *J–V data for a Cs2TeBr6 device at various temperatures used to extract
 hole mobility. "Forward Bias" and "Reverse Bias" are
 at 280 K.* "Forward Bias – SCLC.csv" "Reverse Bias –
 SCLC.csv" "280 K Mobility Fit – SCLC.csv" "270 K
 Mobility Fit – SCLC.csv" "260 K Mobility Fit – SCLC.csv"
 "250 K Mobility Fit – SCLC.csv" "240 K Mobility Fit –
 SCLC.csv" "230 K Mobility Fit – SCLC.csv" "220 K
 Mobility Fit – SCLC.csv" * Current (A) and voltage (V) raw data
 collected with Keithley 2400 * Data from 0 V to 0.5 V was fit to
 Ohm's law to extract the shunt resistance, which was then used to
 subtract shunt background current from the raw data to successfully fit
 SCLC curve ### Figure S1 *Cross-sectional images of a Cs2TeBr6 film made
 by spinning TeBr4 at 4000 rpm followed by CsBr at 2000 rpm. The film was
 grown on a silicon substrate which was broken in half to view the
 cross-section at the middle of the film.* "Film Cross-Section –
 SEM.tif" "Film Cross-Section Zoomed-In – SEM.tif" * Raw
 TIFF file of SEM images ### Figure S2 *Time evolution of emission from
 CsPbBr3 and Cs2TeCl6 films made via a two-step deposition process. CsX
 solution was deposited at t = 0 s. Additional emission features centered
 around 2.75 eV and 1.60 eV are likely a measurement artifact intensified
 because of the relatively low PL emission intensity.* "Cs2TeCl6 –
 In-situ PL.csv" "CsPbBr3 – In-situ PL.csv" * Folder of
 wavelength (nm) and emission intensity raw data files  * Number in the
 file name indicates the order of collection, with each data point captured
 with an integration time of 0.5 s "Cs2TeCl6 Peak Locations – In-situ
 PL.csv" "CsPbBr3 Peak Locations – In-situ PL.csv" * Time
 (s), peak position (eV), and emission intensity from Gaussian fit of raw
 emission data ### Figure S3 *GIWAXS images of Cs2TeBr6 films made with 0.5
 M, 1 M, and 1.5 M CsBr solution.* "0.5 M CsBr Detector Image –
 GIWAXS.tif" "1 M CsBr Detector Image – GIWAXS.tif"
 "1.5 M CsBr Detector Image – GIWAXS.tif" * Raw TIFF files of
 GIWAXS detector images ### Figure S4 *Azimuthally integrated GIWAXS data
 of Cs2TeBr6 films acquired with varying grazing-incidence angle. The pink
 shaded region marks the most prominent TeBr4 reflection. Films were made
 by spinning 50 uL of 1 M TeBr4 at 2000 rpm followed by 50 uL of 1 M CsBr
 deposited dynamically at 2000 rpm.* "0.2° Detector Image –
 GIWAXS.tif" "0.5° Detector Image – GIWAXS.tif" "1°
 Detector Image – GIWAXS.tif" "2° Detector Image –
 GIWAXS.tif" * Raw TIFF files of GIWAXS detector images "0.2°
 Integrated Signal – GIWAXS.csv" "0.5° Integrated Signal –
 GIWAXS.csv" "1° Integrated Signal – GIWAXS.csv" "2°
 Integrated Signal – GIWAXS.csv" * GIWAXS data after making geometric
 corrections with Nika and integrating with WAXStools * *q* (A⁻¹) and
 integrated intensity data ### Figure S5 *XPS scans of a Cs2TeBr6 film in
 binding energy regions for cesium, tellurium, and bromide. The film was
 made by spin-coating 1 M TeBr4 at 2000 rpm followed by 1 M CsBr at 2000
 rpm.* "Bromine Scan – XPS.csv" "Cesium Scan – XPS.csv"
 "Tellurium Scan – XPS.csv" * Kinetic energy (eV) and intensity
 raw XPS data ### Figure S6 *XPS scans of a TeBr4 film in binding energy
 regions for tellurium and bromide.* "Bromine Scan – XPS.csv"
 "Tellurium Scan – XPS.csv" * Kinetic energy (eV) and intensity
 raw XPS data ### Figure S8 *Azimuthally integrated GIWAXS data collected
 at a 3° incidence angle of Cs2TeBr6 film made by depositing both layers at
 6000 rpm.* "6000 rpm Detector Image – GIWAXS.tif" * Raw TIFF
 file of GIWAXS detector image "6000 rpm Integrated Signal –
 GIWAXS.csv" * GIWAXS data after making geometric corrections with
 Nika and integrating with WAXStools * *q* (A⁻¹) and integrated intensity
 data ### Figure S9 *SEM images of films made by varying the spin speed of
 both the first TeBr4 layer and the second CsBr layer.* "2000 rpm
 First Layer 2000 rpm Second Layer – SEM.tif" "2000 rpm First
 Layer 4000 rpm Second Layer – SEM.tif" "2000 rpm First Layer
 8000 rpm Second Layer – SEM.tif" "4000 rpm First Layer 2000 rpm
 Second Layer – SEM.tif" "4000 rpm First Layer 4000 rpm Second
 Layer – SEM.tif" "4000 rpm First Layer 8000 rpm Second Layer –
 SEM.tif" * Raw TIFF files of SEM images ### Figure S10 *PXRD patterns
 for Cs2TeCl6 and Cs2TeI6 formed via two-step spin-coating.* "Cs2TeCl6
 – PXRD.csv" "Cs2TeI6 – PXRD.csv" * Measurement conditions
 of PXRD experiment * *2θ* angle (°) and intensity raw data ### Figure S11
 *XPS scan of a film made by spin-coating 1 M TeBr4 and 1 M CsCl in the
 binding energy region for chlorine. There are no photoemission peaks in
 the spectrum.* "Chlorine Scan – XPS.csv" * Kinetic energy (eV)
 and intensity raw XPS data ### Figure S12 *Azimuthally integrated GIWAXS
 data collected at a 3° incidence angle of a film made by depositing CsI on
 top of TeBr4 via a two-step deposition.* "0.5 M TeBr4 + 1 M CsI
 Detector Image – GIWAXS.tif" * Raw TIFF file of GIWAXS detector image
 "0.5 M TeBr4 + 1 M CsI Integrated Signal – GIWAXS.csv" * GIWAXS
 data after making geometric corrections with Nika and integrating with
 WAXStools * *q* (A⁻¹) and integrated intensity data ### Figure S13 *UPS
 spectrum of Cs2TeBr6 film with fiGed energy onset and cutoﬀ.*
 "Cs2TeBr6 Valence Band – UPS.csv" * Kinetic energy (eV) and
 intensity raw UPS data ### Figure S14 *XPS scans of a Cs2TeBr6 device in
 binding energy regions for cesium, tellurium, and bromide. The film was
 made by spin-coating 1 M TeBr4 at 4000 rpm followed by 1.5 M CsBr at 2000
 rpm.* "Bromine Scan – XPS.csv" "Cesium Scan – XPS.csv"
 "Tellurium Scan – XPS.csv" * Kinetic energy (eV) and intensity
 raw XPS data ### Figure S15 *J-V curve for Cs2TeBr6 SCLC diode held at 280
 K used to extract hole mobility value.* "280 K Mobility Fit –
 SCLC.csv" * Current (A) and voltage (V) raw data collected with
 Keithley 2400 * Data from 0 V to 0.5 V was fit to Ohm's law to
 extract the shunt resistance, which was then used to subtract shunt
 background current from the raw data to successfully fit SCLC curve ###
 Figure S16 *J-V curves for Cs2TeBr6 SCLC diode acquired at various
 temperatures to extract hole mobility value.* "280 K Mobility Fit –
 SCLC.csv" "270 K Mobility Fit – SCLC.csv" "260 K
 Mobility Fit – SCLC.csv" "250 K Mobility Fit – SCLC.csv"
 "240 K Mobility Fit – SCLC.csv" "230 K Mobility Fit –
 SCLC.csv" "220 K Mobility Fit – SCLC.csv" * Current (A) and
 voltage (V) raw data collected with Keithley 2400 * Data from 0 V to 0.5 V
 was fit to Ohm's law to extract the shunt resistance, which was then
 used to subtract shunt background current from the raw data to
 successfully fit SCLC curve