Starting materials: CH3NH3I [from synthesis], SnI2 [from synthesis], distilled HI 57% aqueous (99.95%), H3PO2 (50% aqueous)

Product: Black MASnI3 crystals

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve SnI2 (372 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid CH3NH3I (159 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Discontinue stirring and leave the solution to cool back to room temperature. Upon cooling, black, elongated, rhombic dodecahedral (12 faces) crystals of the title compound were precipitated. Leave crystals to grow for a further 24 h under a nitrogen atmosphere before filtering and washing copiously with degassed EtOH. Yield 70-90%.

Method: Optical-diffuse reflectance

Description: Measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation: α/S =(1 − R)^2/2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Refer to Page 9029 Figure 9.

• Rayan C Duke University

Starting materials: HC(NH2)2I [from synthesis], SnI2 [from synthesis], distilled HI 57% aqueous (99.95%), H3PO2 (50% aqueous)

Product: Black FASnI3 crystals

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve SnI2 (372 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid HC(NH2)2I (172 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Discontinue stirring and leave the solution to cool back to room temperature. Upon cooling, black rhombic dodecahedral crystals (12 faces) of the title compound were precipitated. Leave crystals to grow for a further 24 h under a nitrogen atmosphere before filtering and washing copiously with degassed EtOH. Yield 70-90%.

Method: Optical-diffuse reflectance

Description: Measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation: α/S =(1 − R)^2/2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Refer to Page 9029 Figure 9.

• Rayan C Duke University

Starting materials: CH3NH3I [from syn], PbI2 [from syn], distilled HI 57% aqueous (99.95%), H3PO2 (50% aqueous)

Product: Black MAPbI3 crystals

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve PbI2 (462 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid CH3NH3I (159 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Discontinue stirring and leave the solution to cool back to room temperature. Upon cooling, black, rhombic dodecahedral crystals (12 faces) of the title compound precipitated. Leave crystals to grow for a further 24 h under a nitrogen atmosphere before filtering and washing copiously with degassed EtOH. Yield 70-90%.

Method: Optical-diffuse reflectance

Description: Measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation: α/S =(1 − R)^2/2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Refer to Page 9029 Figure 9.

• Rayan C Duke University

Starting materials: HC(NH2)2I, PbI2, distilled HI (57% aqueous) (99.95%), H3PO2 (50% aqueous)

Product: Black FAPbI3 Crystals (α phase)

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve PbI2 (462 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid HC(NH2)2I (172 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Stop stirring and leave solution to evaporate at 100 °C. Black hexagonal (8 faces) or trigonal (5 faces) crystals of the title compound were precipitated and grown at this temperature. After standing for 2-3 h at 100 °C, under a nitrogen atmosphere, set temperature to 80 °C for a further 2-3 h. Repeat the previous step for two more times to reach 60 °C and 40 °C at which point the solution was left to come to room temperature by powering off the hotplate. The crystals were collected by filtration and washed with anhydrous EtOH.

Method: Optical-diffuse reflectance

Description: Optical diffuse-reflectance measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation: α/S =(1 − R)^2/2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Refer to Page 9029 Figure 9.

Comment: Black FAPbI3 Crystals (α phase)

• Rayan C Duke University

Starting materials: CH3NH3I, SnI2

Product: Black MASnI3 Solid

Description: Load equimolar amounts of SnI2 and MAI in a 9mm pyrex tube. Shake materials mechanically to ensure a homogenous mixture. Place tube on a sealing line evacuated to 10-4 mbar and flame sealed. Immerse tube on a sand bath standing at 200 °C, such that the mixture of solids was heated homogeneously. Maintain 4/5 of the tube outside the bath at room temperature. Leave solids in the bath for 2 h to form a homogeneous black solid. The Sn containing solids are air sensitive. No obvious color changes are observed.

Method: Optical-diffuse reflectance

Description: Measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation. Refer to Page 9029 Figure 9.

• Rayan C Duke University

Starting materials: CH3NH3I, PbI2

Product: Black MAPbI3 Solid

Description: Load equimolar amounts of PbI2 and MAI in a 9mm pyrex tube. Shake materials mechanically to ensure a homogenous mixture. Place the tube on a sealing line evacuated to 10-4 mbar and flame sealed. Immerse tube on a sand bath standing at 200 °C, such that the mixture of solids was heated homogeneously. Maintain 4/5 of the tube outside the bath at room temperature. Leave solids in the bath for 2 h to form a homogeneous black solid.

Method: Optical-diffuse reflectance

Description: Measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation: α/S =(1 − R)^2/2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Refer to Page 9029 Figure 9.

• Rayan C Duke University

Starting materials: CH3NH3I, SnI2

Product: Black MASnI3 Ingot

Description: Load equimolar amounts of SnI2 and MAI in a 15mm pyrex test tube. Shake materials mechanically to ensure a homogenous mixture. Immerse in a sand bath standing at 350 °C under a gentle flow of nitrogen. The reaction proceeds within 0.5-1 min. The formation of a homogeneous black melt signals the end of the reaction. Upon melting the tube was removed from the bath and left to cool in air, usually producing a shiny black ingot.

Method: Optical-diffuse reflectance

Description: Measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation: α/S =(1 − R)^2/2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Refer to Page 9029 Figure 9.

• Rayan C Duke University

Starting materials: CH3NH3I, PbI2

Product: Black MAPbI3 Ingot

Description: Load equimolar amounts of PbI2 and MAI in a 15mm pyrex test tube. Shake materials mechanically to ensure a homogenous mixture. Immerse in a sand bath standing at 350 °C under a gentle flow of nitrogen. The reaction proceeds within 0.5-1 min. Pb-containing solids decompose on prolonged heating (> 3 min) or by raising the temperature above 400 °C, through evolution of I2 gas, crystallizing on the cooler walls of the tube.

Method: Optical-diffuse reflectance

Description: Measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation: α/S =(1 − R)^2/2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Refer to Page 9029 Figure 9.

• Rayan C Duke University

Starting materials: CH3NH3I, SnI2

Product: Black MASnI3 Powder

Description: Place equimolar amounts of SnI2 and MAI in an agate mortar and ground carefully with a pestle until a visually homogeneous, black powder is obtained.

Method: Optical-diffuse reflectance

Description: Measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation: α/S =(1 − R)^2/2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Refer to Page 9029 Figure 9.

• Rayan C Duke University

Starting materials: CH3NH3I, PbI2

Product: Black MAPbI3 Powder

Description: Place equimolar amounts of PbI2 and MAI in an agate mortar and ground carefully with a pestle until a visually homogeneous, black powder is obtained.

Method: Optical diffuse reflectance

Description: Measurements were performed at room temperature using a Shimadzu UV-3101 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO4 was used as a nonabsorbing reflectance reference. The generated reflectance-versus-wavelength data were used to estimate the band gap of the material by converting reflectance to absorbance data according to the Kubelka−Munk equation: α/S =(1 − R)^2/2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Refer to Page 9029 Figure 9.

• Rayan C Duke University

Starting materials: CH3NH3I [from synthesis], SnI2 [from synthesis], distilled HI (57% aqueous) (99.95%), H3PO2 (50% aqueous)

Product: Black MASnI3 crystals

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve SnI2 (372 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid CH3NH3I (159 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Discontinue stirring and leave the solution to cool back to room temperature. Upon cooling, black, elongated, rhombic dodecahedral (12 faces) crystals of the title compound were precipitated. Leave crystals to grow for a further 24 h under a nitrogen atmosphere before filtering and washing copiously with degassed EtOH.

Method: Single crystal X-ray diffraction

Description: Single-crystal X-ray diffraction experiments were performed using either a STOE IPDS II or IPDS 2T diffractometer using Mo Kα radiation (λ = 0.71073 Å) and operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using the X-AREA, X-RED, and X-SHAPE programs. Refer to Page 9025 Table 1.

• Rayan C Duke University

Starting materials: HC(NH2)2I [from synthesis], SnI2 [from synthesis], distilled HI (57% aqueous) (99.95%), H3PO2 (50% aqueous)

Product: Black FASnI3 crystals

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve SnI2 (372 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid HC(NH2)2I (172 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Discontinue stirring and leave the solution to cool back to room temperature. Upon cooling, black rhombic dodecahedral crystals (12 faces) of the title compound were precipitated. Leave crystals to grow for a further 24 h under a nitrogen atmosphere before filtering and washing copiously with degassed EtOH.

Method: Single crystal X-ray diffraction

Description: Single-crystal X-ray diffraction experiments were performed using either a STOE IPDS II or IPDS 2T diffractometer using Mo Kα radiation (λ = 0.71073 Å) and operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using the X-AREA, X-RED, and X-SHAPE programs. Refer to Page 9025 Table 1.

• Rayan C Duke University

Starting materials: CH3NH3I [from syn], PbI2 [from syn], distilled HI (57% aqueous) (99.95%), H3PO2 (50% aqueous)

Product: Black MAPbI3 crystals

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve PbI2 (462 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid CH3NH3I (159 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Discontinue stirring and leave solution to cool back to room temperature. Upon cooling, black, rhombic dodecahedral crystals (12 faces) of the title compound precipitated. Leave crystals to grow for a further 24 h under a nitrogen atmosphere before filtering and washing copiously with degassed EtOH.

Method: Single crystal X-ray diffraction

Description: Single-crystal X-ray diffraction experiments were performed using either an STOE IPDS II or IPDS 2T diffractometer using Mo Kα radiation (λ = 0.71073 Å) and operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using the X-AREA, X-RED, and X-SHAPE programs. Refer to Page 9025 Table 1.

• Rayan C Duke University

Starting materials: HC(NH2)2I, PbI2,distilled HI (57% aqueous) (99.95%), H3PO2 (50% aqueous)

Product: Black FAPbI3 Crystals (alpha phase)

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve PbI2 (462 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid HC(NH2)2I (172 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Stop stirring and leave the solution to evaporate at 100 °C. Black hexagonal (8 faces) or trigonal (5 faces) crystals of the title compound were precipitated and grown at this temperature. After standing for 2-3 h at 100 °C, under a nitrogen atmosphere, set the temperature to 80 °C for a further 2-3 h. Repeat the previous step for two more times to reach 60 °C and 40 °C at which point the solution was left to come to room temperature by powering off the hotplate. The crystals were collected by filtration and washed with anhydrous EtOH.

Method: Single crystal X-ray diffraction

Description: Single-crystal X-ray diffraction experiments were performed using either an STOE IPDS II or IPDS 2T diffractometer using Mo Kα radiation (λ = 0.71073 Å) and operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using the X-AREA, X-RED, and X-SHAPE programs. Refer to page 9025 Table 1.

Comment: This compound was assigned the trigonal space group P3m1 in the original publication (doi: 10.1021/ic401215x) and this assignment is therefore retained here. However, the literature consensus for the alpha phase of formamidinium, including a later report by some of the same authors (https://doi.org/10.1002/anie.201609538), is that the compound crystallizes in the cubic space group Pm-3m. Those later reports are considered more accurate.

Starting materials: CH3NH3I [from synthesis], SnI2 [from synthesis], distilled HI (57% aqueous) (99.95%), H3PO2 (50% aqueous)

Product: Black MAPbI3 crystals

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve SnI2 (372 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid CH3NH3I (159 mg, 1 mmol). Evaporate the solution to approximately half its original volume by heating at 120 °C. Discontinue stirring and leave the solution to cool back to room temperature. Upon cooling, black, elongated, rhombic dodecahedral (12 faces) crystals of the title compound were precipitated. Leave crystals to grow for a further 24 h under a nitrogen atmosphere before filtering and washing copiously with degassed EtOH. Yield 70-90%.

Method: Single crystal X-ray diffraction

Description: Single-crystal X-ray diffraction experiments were performed using either an STOE IPDS II or IPDS 2T diffractometer using Mo Kα radiation (λ = 0.71073 Å) and operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using the X-AREA, X-RED, and X-SHAPE programs. Refer to Page 9025 Table 2.

• Rayan C Duke University

Starting materials: HC(NH2)2I [from synthesis], SnI2 [from synthesis], distilled HI (57% aqueous) (99.95%), H3PO2 (50% aqueous)

Product: Black FASnI3 crystals

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve SnI2 (372 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid HC(NH2)2I (172 mg, 1 mmol). Evaporate the solution to approximately half its original volume by heating at 120 °C. Discontinue stirring and leave the solution to cool back to room temperature. Upon cooling, black rhombic dodecahedral crystals (12 faces) of the title compound were precipitated. Leave crystals to grow for a further 24 h under a nitrogen atmosphere before filtering and washing copiously with degassed EtOH. Yield 70-90%.

Method: Single crystal X-ray diffraction

Description: Single-crystal X-ray diffraction experiments were performed using either an STOE IPDS II or IPDS 2T diffractometer using Mo Kα radiation (λ = 0.71073 Å) and operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using the X-AREA, X-RED, and X-SHAPE programs. Refer to Page 9025 Table 2.

• Rayan C Duke University

Starting materials: CH3NH3I [from syn], PbI2 [from syn], distilled HI 57% (99.95%), H3PO2 50%

Product: Black MAPbI3 crystals

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve PbI2 (462 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid CH3NH3I (159 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Discontinue stirring and leave solution to cool back to room temperature. Upon cooling, black, rhombic dodecahedral crystals (12 faces) of the title compound precipitated. Leave crystals to grow for a further 24 h under a nitrogen atmosphere before filtering and washing copiously with degassed EtOH. Yield 70-90%.

Method: Single crystal X-ray diffraction

Description: Single-crystal X-ray diffraction experiments were performed using either an STOE IPDS II or IPDS 2T diffractometer using Mo Kα radiation (λ = 0.71073 Å) and operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using the X-AREA, X-RED, and X-SHAPE programs. Refer to Page 9025 Table 2.

• Rayan C Duke University

Starting materials: HC(NH2)2I, PbI2, distilled HI 57% aqueous (99.95%), H3PO2 (50% aqueous)

Product: Black FAPbI3 Crystals (alpha phase)

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve PbI2 (462 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid HC(NH2)2I (172 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Stop stirring and leave solution to evaporate at 100 °C. Black hexagonal (8 faces) or trigonal (5 faces) crystals of the title compound were precipitated and grown at this temperature. After standing for 2-3 h at 100 °C, under a nitrogen atmosphere, set temperature to 80 °C for a further 2-3 h. Repeat the previous step for two more times to reach 60 °C and 40 °C at which point the solution was left to come to room temperature by powering off the hotplate. The crystals were collected by filtration and washed with anhydrous EtOH.

Method: Single crystal X-ray diffraction

Description: Single-crystal X-ray diffraction experiments were performed using either a STOE IPDS II or IPDS 2T diffractometer using Mo Kα radiation (λ = 0.71073 Å) and operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using the X-AREA, X-RED, and X-SHAPE programs. Refer to Page 9025 Table 2.

• Rayan C Duke University

Starting materials: HC(NH2)2I, PbI2, distilled HI 57% (99.95%), H3PO2 50%

Product: Yellow FAPbI3 Crystals (delta phase)

Description: Charge 100 ml 2-necked round bottom flask with a mixture of aqueous HI (6.8 ml, 7.58M) and aqueous H3PO2 (1.7 ml, 9.14M). The liquid was degassed by passing a stream of nitrogen through it for 1 min and keeping it under a nitrogen atmosphere throughout the experiment. Dissolve PbI2 (462 mg, 1 mmol) in the mixture upon heating the flask to 120 °C using an oil bath, under constant magnetic stirring, forming a bright yellow solution. Add solid HC(NH2)2I (172 mg, 1 mmol). Evaporate solution to approximately half its original volume by heating at 120 °C. Stop stirring and leave solution to evaporate at 100 °C. Black hexagonal (8 faces) or trigonal (5 faces) crystals of the title compound were precipitated and grown at this temperature. Discontinue heating and cool the mixture to room temperature. After 4-5 h the black crystals fully convert to yellow ones of essentially the same shape. Collect yellow crystals by filtration and wash copiously with anhydrous EtOH. Yield 50-60%. The crystals are insensitive on exposure to the atmosphere but spontaneously hydrolyse to yellow PbI2 upon wetting in H2O.

Method: Single crystal X-ray diffraction

Description: Single-crystal X-ray diffraction experiments were performed using either a STOE IPDS II or IPDS 2T diffractometer using Mo Kα radiation (λ = 0.71073 Å) and operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using the X-AREA, X-RED, and X-SHAPE programs. Refer to Page 9025 Table 3.

• Rayan C Duke University