Starting materials: HI, CH3NH2, Pb(NO3)2

Product: Partially deuterated MAPbI3

Description: Add concentrated HI to neutralize 20 g of 40% CH3NH2 aqueous solution. Add 7.1 g (0.021 mol) of Pb(NO3)2 solution drop-wise under vigorous stirring at 100°C to the concentrated CH3NH2I solution. Organic crystals form while dripping in the solution. Cool the solution to not below 40°C and filter out the crystals. Wash crystals firstly with n-butanol and then with benzene; subsequently dry crystals in vacuum. Partially N-deuterated samples required for the NMR studies were prepared using D-containing solutions. Refer to Page 413 Experimental.

Comment: Synthesis references: [1] Canadian Journal of Chemistry, 1987, 65(5): 1042-1046 https://doi.org/10.1139/v87-176 [2] D. WEBER. Z. Naturforsch. 33b, 1443 (1978).

Method: 2H and 14N NMR

Description: Measurements were carried out at 8.48 T with a Nicolet 360NB spectrometer using a broad band (16-58 MHz) variable-temperature 10 mm probe supplied by Nicolet. The 2-H and 14-N frequencies were 55.427 and 26.083 MHz, respectively. Refer to Page 414 Results section Existence of transitions subsection.

• Rayan C Duke University

Starting materials: HI, CH3NH2, Pb(NO3)2

Product: N-deuterated MAPbI3 crystals

Description: Add concentrated HI to neutralize 20 g of 40% CH3NH2 aqueous solution (D2O-H2O mixture). Add 7.1 g (0.021 mol) of Pb(NO3)2 solution drop-wise under vigorous stirring at 100°C to the concentrated CH3NH3I solution. Organic crystals form while dripping in the solution. Cool the solution to not below 40°C and filter out the crystals. Wash crystals firstly with n-butanol and then with benzene; subsequently dry crystals in vacuum.

Comment: Synthesis references: [1] D. Weber, Z. Naturforsch. 33b, 1443 (1978).

Method: 2H and 14N NMR

Description: 2H and 14N NMR spectra were recorded at 55.4257 and 26.083 MHz, respectively, on a Nicolet 360 NB spectrometer (B0 = 8.48 T). Refer to Page 581.

• Rayan C Duke University

Starting materials: Pb(CH3CO2)2, MAI

Product: Black MAPbI3 cube-shaped crystals of 1-2 mm

Description: Add aqueous solution of Pb(CH3CO2)2 drop by drop to an excess quantity of hot aqueous MAI solution and cool slowly, keeping temperature above 40 °C to prevent crystallization of (MA)3Pb6-2H2O.

Method: Adiabatic calorimetry

Description: The heat capacities were measured with a computerized adiabatic calorimeter [1, 2]. The temperature ranges of the measurement were between 13 and 365 K. The mass of the calorimetric sample was 9.3384 g.

Comment: References: [1] Tatsumi M., Matsuo T., Suga H. and Seki S., Bull. chem. Soc. Jap. 48, 3060 (1975). [2] Matsuo T. and Suga H., Thermochim. Acta 88, 149 (1985).

• Rayan C Duke University

Starting materials: lead (II) acetate, CH3NH3+ (by adding a 40% solution of CH3NH2 in water), concentrated HI

Product: Black MAPbI3 crystals

Description: CH3NH3PbI3 was synthesized from lead (II) acetate and CH3NH3+ dissolved in a concentrated HI solution. The aqueous solution was cooled from l00°C to 40°C to obtain the black crystals.

Method: Temperature-dependent Guinier-Simon photograph

Description: No method specified. Refer to Page 6374 Table I.

• Rayan C Duke University

Starting materials: Methylamine (40% in methanol), hydroiodic acid (57 wt% in water), PbI2, g-butyrolactone, H2O2, NH4OH, Si wafer

Product: MAPbI3 film

Description: React 30 mL of methylamine and 32.3 mL of hydroiodic acid at 0 °C for 2 h. Evaporate solvents at 50 °C. Wash the yellowish raw CH3NH3I with diethyl ether by stirring the solution for 30min for a total of three times. Recrystallize CH3NH3I from a mixed solvent of diethyl ether and ethanol. Collect the solid and dry at 60 °C in a vacuum oven for 24 h. Treat Si wafer with an aqueous solution of H2O2 and NH4OH with a volume ratio of H2O2 : NH4OH : H2O = 1 : 1 : 5 for 30 min. Drop a 40 wt% precursor solution of equimolar CH3NH3I and PbI2 in g-butyrolactone onto the Si wafer to form the MAPbI3 film. Spin-coat at 1500 rpm for 30 s, and then at 2500 rpm for 40 min in air. Upon drying at room temperature, color change indicates the formation of MAPbI3 in the solid state. Anneal the MAPbI3 film in air for 15 min at 100 °C.

Method: Powder X-ray diffraction

Description: No experimental details. Coexistence of the two phases at T from 150 to 130 K.

• Rayan C Duke University

Starting materials: HI (conc), PbAc2, CH3NH3+

Product: Black MAPbI3 Crystals

Description: Precipitate product from a concentrated aqueous solution of hydroiodic acid containing lead(II) acetate and a respective amount of CH3NH3+ solution. The two ends of the sample holder were held at 55 and 42 °C respectively to induce the saturation of the solute at the low temperature part of the solution. After 24 h submillimeter sized crystals appeared in the solution.

Comment: Both large and small crystals were grown. Large MAPbI3 crystals with 3 x 5 mm silver-gray mirror-like facets were grown after 7 days [Figure 1]. Smaller crystals were ground in a mortar and pressed together to obtain a mechanically stable polycrystalline sample [Figure 2].

Method: Thermocouple: Temperature dependence of thermal conductivity

Description: Conducted for 3 samples. Swept down from 310 K to 25 K. Using a steady-state method using calibrated stainless steel as reference sample (Page 2491 Figure 5). Refer to Page 2489 Figure 4.

Comment: For the SC samples the width of this dip is only 2 K.

• Rayan C Duke University

Starting materials: HI (conc), PbAc2, CH3NH3+

Product: Black MAPbI3 Crystals

Description: Precipitate product from a concentrated aqueous solution of hydroiodic acid containing lead(II) acetate and a respective amount of CH3NH3+ solution. The two ends of the sample holder were held at 55 and 42 °C respectively to induce the saturation of the solute at the low temperature part of the solution. After 24 h submillimeter sized crystals appeared in the solution.

Comment: Both large and small crystals were grown. Large MAPbI3 crystals with 3 x 5 mm silver-gray mirror-like facets were grown after 7 days [Figure 1]. Smaller crystals were ground in a mortar and pressed together to obtain a mechanically stable polycrystalline sample [Figure 2].

Method: Thermocouple: Temperature dependence of thermal conductivity

Description: Conducted for 3 samples. Swept down from 310 K to 25 K. Using a steady-state method using calibrated stainless steel as reference sample (Page 2491 Figure 5). Refer to Page 2489 Figure 4.

Comment: PC samples the structural transition is smeared over a wider temperature range, corresponding to approximately 8 K.

• Rayan C Duke University

Starting materials: Lead(II) acetate (Chemical Reagents, Sigma), aqueous HI, CH3NH2 (40% soluble in water, Merck)

Product: Black MAPbI3 Polycrystals

Description: Following method by [1], dissolve 2.5 g of lead(II) acetate in 10 ml of concentrated (57% by weight) aqueous HI contained in a pyrex test tube and heat in a water bath. Add an additional 2 ml of HI solution with 0.597 g of CH3NH2 to the solution. Filter the black precipitate upon cooling from 100 °C to 46 °C over 6 hours and dry (100 °C/10 hours). Maintain solution temperature above 40 °C. Black crystals up to 2 mm long were obtained by cooling the solution over 4 days. Crystallization proceeded most rapidly at approximately 70 °C.

Comment: Synthesis references: [1] A. Poglitsch and D. Weber, J. Chem. Phys., 1987, 87, 6373–6378. [2] J. H. Im, C. R. Lee, J. W. Lee, S. W. Park and N. G. Park, Nanoscale, 2011, 3, 4088–4093.

Method: Powder X-ray diffraction

Description: Tetragonal/cubic phase transition was investigated using variable temperature powder X-ray diffraction. In situ XRD data were collected in asymmetric reflection mode under a static helium atmosphere on an INEL Equinox 3000 (Inel, Artenay, France) equipped with an XRK-900 reactor chamber (Anton-Paar, Graz, Austria), a curved position sensitive detector (Ine, Artenay, France), a copper Ka source and a Ge-(111) focussing mirror. Two different heating experiments were conducted. In the first, MAPbI3 was heated to 85 °C in five degree steps starting from 25 °C, with data collected for 5 minutes at each holding temperature. The second experiment employed a continuous heating ramp at a rate of 1° min^-1 during which 30 measurements of 120 seconds were performed. Each measurement corresponds to a temperature span of 2 °C; the final temperature of each measurement was recorded in the measurement file. Five empty sample holder measurements were conducted at room temperature in order to establish the chamber background. Refer to Page 5633 Results and discussion; Page 5634 Figure 4 and Figure 5.

Comment: Transition approximately from (327 - 330 K, 54 - 57 °C), large change in diffraction intensity at 57 °C weak scattering persists up to 75 °C on heating collected at 2 °C intervals.

• Rayan C Duke University

Starting materials: HI (Sigma Aldrich), methylamine, PbI2 (99%, Sigma Aldrich), gamma-butyrolactone (Sigma Aldrich)

Product: Black MAPbI3 Single crystals

Description: MAPbI3 was synthesized using the method described by [2]. Make MAI by reacting a concentrated aqueous solution of hydroiodic acid with methylamine (40% in methanol) at 0 °C for 2 h with constant stirring. Evaporate at 50 °C in a rotary evaporator and wash the resulting precipitant three times with ethyl ether and dry in a vacuum at 60 °C for 24 h. Equimolar mixtures of the as-synthesised MAI and PbI2 in gamma-butyrolactone were left to stir overnight at 60 °C. The MAPbI3 product was obtained by drop-casting the as-prepared solutions on to glass substrates, which were then heated to 100 °C and annealed for 30 min. Crystalline MAPbI3 was recovered from the glass after cooling.

Comment: Synthesis references: [1] A. Poglitsch and D. Weber, J. Chem. Phys., 1987, 87, 6373–6378. [2] J. H. Im, C. R. Lee, J. W. Lee, S. W. Park and N. G. Park, Nanoscale, 2011, 3, 4088–4093.

Method: Single crystal X-ray diffraction

Description: A small fragment (approximately 0.1 mm X 0.1 mm X 0.1 mm) was cleaved from one of the solution grown single crystals. Data were collected on a Bruker Smart Apex II three-circle diffractometer at various temperatures between room temperature and 100 K using Mo Ka radiation with a graphite monochromator over the angular range 2.5 to 30.5 ° 2\theta. Refer to Page 5637 Figure 11.

Comment: Author did not formally state 152 K as the transition temperature. But lattice parameters provided in Table 8 supports this conclusion.

• Rayan C Duke University

Starting materials: CD3ND2DCl (Sigma-Aldrich, 98 atom % D), DI, D2O, PbI2 (Acros Organics)

Product: Black d6-MAPbI3 Powder

Description: Dissolve 1.0 g of CD3ND2DCl in 15 g of 16% DI in D2O (made by dissolving 5 g DI gas in 25 g D2O) and pump to dryness to yield CD3ND2DI. Add material to 6 g of lead iodide and mix in ~25mL of DMF. Upon stirring, obtain pale yellow clear solution. Warm resulting solution and stir overnight in a N2 glove box. Evaporate solution to dryness under vacuum and wash the resulting black solution with dichloromethane and n-propanol. Isolate using suction drying. Anneal solid in nitrogen in the glove box at 140 °C for 1hr to remove residual solvent. Expect to yield 7.95 g of d6-MAPbI3 (97% yield).

Comment: MAPbI3 (d6-CD3ND3PbI3)

Method: Neutron diffraction

Description: Samples were loaded into 8mm diameter vanadium cans in a helium glove- box for analysis on the POWGEN diffractometer situated at the Spallation Neutron Source, Oak Ridge National Laboratory. The analyses of the POWGEN data were carried out using the TOPAS refinement package for Rietveld. Heating and cooling rates were 1K/min. Refer to Page 10 Table 2.

• Rayan C Duke University

Starting materials: CD3ND2DCl (Sigma-Aldrich, 98 atom % D), DI, D2O, PbI2 (Acros Organics)

Product: Black d6-MAPbI3 Powder

Description: Dissolve 1.0 g of CD3ND2DCl in 15 g of 16% DI in D2O (made by dissolving 5 g DI gas in 25 g D2O) and pump to dryness to yield CD3ND2DI. Add material to 6 g of lead iodide and mix in ~25mL of DMF. Upon stirring, obtain pale yellow clear solution. Warm resulting solution and stir overnight in a N2 glove box. Evaporate solution to dryness under vacuum and wash the resulting black solution with dichloromethane and n-propanol. Isolate using suction drying. Anneal solid in nitrogen in the glove box at 140 °C for 1hr to remove residual solvent. Expect to yield 7.95 g of d6-MAPbI3 (97% yield).

Comment: MAPbI3 (d6-CD3ND3PbI3)

Method: Synchrotron X-ray powder diffraction

Description: The X-ray powder diffraction measurements were performed on the bending magnet station at DND-CAT sector 5 of the Advanced Photon Source. The X-ray wavelength used was 0.40012(2) Å, selected to reduce X-ray absorption by the sample to an acceptable level. Temperatures were equilibrated for ~10 min after 1 K changes. Refer to Page 10 Table 2.

• Rayan C Duke University

Starting materials: CH3ND3I

Product: Black CH3ND3PbI3 Powder

Description: Preparation of CH3ND3I: React methylamine gas with HI to yield methyl ammonium iodide. Exchange the two H atoms attached to the nitrogen atoms with D by dissolving the salt in 10 ml D2O (99 atom % D), drying under vacuum, and then repeating two more times. The resulting CH3ND3I was estimated to be better than 98 atom% D on the ammonium group. Add material to ~6 g of lead iodide and mix in ~25mL of DMF. Upon stirring, obtain pale yellow clear solution. Warm resulting solution and stir overnight in a N2 glove box. Evaporate solution to dryness under vacuum and wash the resulting black solution with dichloromethane and n-propanol. Isolate using suction drying. Anneal solid in nitrogen in the glove box at 140 °C for 1hr to remove residual solvent.

Comment: MAPbI3 (d3-CH3ND3PbI3)

Method: Neutron diffraction

Description: Samples were loaded into 8mm diameter vanadium cans in a helium glove-box for analysis on the POWGEN diffractometer situated at the Spallation Neutron Source, Oak Ridge National Laboratory. The analyses of the POWGEN data were carried out using the TOPAS refinement package for Rietveld. Heating and cooling rates were 1K/min. Refer to Page 10 Table 2.

• Rayan C Duke University

Product: Black MAPbI3 Powder

Description: Not explicitly stated in article. But assume close to synthesis methods of the deuterated compounds. Refer to the related data sets.

Method: Synchrotron X-ray powder diffraction

Description: The X-ray powder diffraction measurements were performed on the bending magnet station at DND-CAT sector 5 of the Advanced Photon Source. The X-ray wavelength used was 0.40012(2) Å, selected to reduce X-ray absorption by the sample to an acceptable level. Temperatures were equilibrated for ~10 min after 1 K changes. Refer to Page 10 Table 2.

• Rayan C Duke University

Starting materials: PbI2, Si substrate, etc.

Product: MAPbI3 Thin-film on Si

Description: Prepare PbI2 aqueous solution (0.1 g per 100 ml) at 80 °C and cool to room temperature, which leads to the formation of suspended PbI2 microplates. For the PL measurement samples, dip the Si substrates with 300nm SiO2 (with pre-fabricated markers by photolithography) into the aqueous solution for a few seconds. For the FET samples, define the 5 nm Cr/50nm Au (Pt) electrodes with channel lengths of 8 and 40 mm by photolithography followed by thermal evaporation and lift-off. Grow PbI2 microplates onto the pre-fabricated electrodes by randomly dispersion. Convert the prepared PbI2 microplates into CH3NH3PbI3 by vapour phase intercalation. Refer to source for more details.

Method: Temperature-dependent transport measurement

Description: The thickness of the perovskite microplates was determined by tapping-mode atomic force microscopy (Vecco 5,000 system). TEM images and SAED patterns were acquired in an FEI Titan high-resolution transmission microscopy. Temperature-dependent FET device measurements were carried out in a probe station ((Lakeshore, TTP4) coupled with a precision source/measurement unit (Agilent B2902A). The scanning rate for the transport measurement is 20V/s and the devices were pre-biased at the opposite voltage for 30 s before each measurement. Refer to Page 3; Page 4 figure 2.

Comment: Film thickness ranging from 30 nm to 400 nm.

• Rayan C Duke University

Starting materials: PbI2, Si substrate, etc.

Product: MAPbI3 Thin-film on Si

Description: Prepare PbI2 aqueous solution (0.1 g per 100 ml) at 80 °C and cool to room temperature, which leads to the formation of suspended PbI2 microplates. For the PL measurement samples, dip the Si substrates with 300nm SiO2 (with pre-fabricated markers by photolithography) into the aqueous solution for a few seconds. For the FET samples, define the 5 nm Cr/50nm Au (Pt) electrodes with channel lengths of 8 and 40 mm by photolithography followed by thermal evaporation and lift-off. Grow PbI2 microplates onto the pre-fabricated electrodes by randomly dispersion. Convert the prepared PbI2 microplates into CH3NH3PbI3 by vapour phase intercalation. Refer to source for more details.

Method: Temperature-dependent photoluminescence

Description: The thickness of the perovskite microplates was determined by tapping-mode atomic force microscopy (Vecco 5,000 system). TEM images and SAED patterns were acquired in an FEI Titan high-resolution transmission microscopy. The PL measurement was conducted under a confocal micro-Raman system (Horiba LABHR) equipped with a 600 g/mm grating in a backscattering configuration excited by an Ar ion laser (488 nm). For the low-temperature measurement, a liquid nitrogen continuous flow cryostat (Cryo Industry of America) was used to control the temperature from 77 to 300 K. Keeping track of the P2/P1 intensity ratio. Increased P2/P1 intensity ratio with decreasing temperature (Fig. 5a and Supplementary Fig. 8).

Comment: Film thickness ranging from <40 nm to 40-200 nm.

• Rayan C Duke University

Starting materials: N/A

Product: MAPbI3 Thin-film on Si

Description: Not described.

Method: Absorption spectra

Description: Absorption spectra was obtained for 350–450 nm-thick perovskite thin-films on glass from room temperature down to 5 K. Samples were mounted in a liquid helium bath cryostat and illuminated with a halogen lamp. Absorption spectra were obtained using a 0.275m focal-length monochromator with a 150 lines/mm or 300 lines/mm grating and detected by a charge-coupled device (CCD) camera. A generalized version of the well-known Elliott formula was used to deduce the exciton binding energies and band gaps at successive temperatures. Refer to Fig. 2&3.

Comment: Thickness 350-450nm

• Rayan C Duke University

Description: Refer to experimental from J. Lumin. 1994, 60&61, 269−274.

Method: Absorption spectra

Description: Experimental data taken from J. Lumin. 1994, 60&61, 269−274 recorded at 159 K (black line) and 212 K (blue line) and computed spectra for bound and continuum pair states, considering two-particle wave function and effective mass equations for electron and hole (expression 3 with γ = 0.03 eV and μ = 0.16me). Structural phase transition occurs at Tc = 162 K (black dashed line). Refer to Fig. 3 and plots from J. Lumin. 1994, 60&61, 269−274.

• Ruyi Song Chemistry department, Duke university

Starting materials: MAI, PbI2, DMF, Si glass

Product: MAPbI3 Thin-film on Si

Description: Dissolve methylammonium iodide and lead (II) iodide (Sigma-Aldrich) in anhydrous N,N-Dimethylformamide (DMF) at a 3:1 molar ratio of MAI to PbI2, with final concentrations of 2.64M methylammonium iodide. The perovskite layer was then formed by spin coating the precursor solutions directly on the glass substrate at 2,000 r.p.m. in air. The flat and thin meso samples were spin coated without dilution but mesoporous samples were spin coated from diluted (three parts in four) precursor solutions. After spin coating, anneal the CH3NH3PbI3 at 150°C for 15 min.

Method: UV-Vis absorption

Description: Absorption measurements were performed using a spectrophotometer (Perkin Elmer Lambda 1050) and a continuous flow static exchange gas cryostat (Oxford Instruments Optistat CF). The cryostat consist of three chambers, one inside the other. The sample is housed inside the internal chamber filled with gaseous He. The cryogenic liquid (He) is fluxed inside the second chamber allowing temperature control of the He atmosphere of the sample chamber. Eventually, a third chamber is evacuated (~10^-5–10^-6 mbar) in order to assure thermal isolation from the external ambient. Refer to Fig. 1.

Comment: Crystal sizes larger than 500nm

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