Supplementary Information for Isothermal Pressure-Derived Metastable States in 2D Hybrid Perovskites Showing Enduring Bandgap Narrowing Gang Liu1, Jue Gong2, Lingping Kong1,3, Richard D. Schaller4,5, Qingyang Hu1, Zhenxian Liu6, Shuai Yan7, Wenge Yang1, Constantinos C. Stoumpos4, Mercouri G. Kanatzidis4, Ho-kwang Mao1,3, and Tao Xu2 1. Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China 2. Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA 3. Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA 4. Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA 5. Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439, USA 6. Institute of Materials Science, Department of Civil and Environmental Engineering, The George Washington University, Washington DC 20052, USA 7. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
Gang Liu; Lingping Kong; Ho-kwang Mao; Tao Xu Email:
[email protected];
[email protected];
[email protected];
[email protected] This PDF file includes: Figs. S1 to S23 Tables S1 to S3 References for SI reference citations
1 www.pnas.org/cgi/doi/10.1073/pnas.1809167115
Fig. S1. Crystal structures of (BA)2PbI4 (n=1), (BA)2MAPb2I7 (n=2), (BA)2(MA)2Pb3I10 (n=3), and (BA)2(MA)3Pb4I13 (n=4) at ambient condition. Here, the compression along c axis for (BA)2PbI4 (n=1) or b axis for (BA)2MAPb2I7 (n=2), (BA)2(MA)2Pb3I10 (n=3), and (BA)2(MA)3Pb4I13 (n=4) are described as layer-to-layer compression.
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Fig. S2. Optical spectra and bandgap determination of (BA)2PbI4 polycrystals at ambient condition. (a) Transmission spectrum of silicone oil measured at 1 atm. Absence of transmission onset indicates that the determination of (BA)2PbI4 bandgap will not be affected by the silicone background signal. (b) Transmission spectrum of (BA)2PbI4 sample in silicone oil at 1 atm. (c) Absorbance spectrum of (BA)2PbI4 at 1 atm. (d) Tauc plot of (BA)2PbI4 with a direct bandgap as 2.29 eV, which was obtained by fitting the linear portion of the plot and extracting at (αdhν)2=0.
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Fig. S3. Optical spectra and bandgap determination for (BA)2(MA)2Pb3I10 polycrystals at ambient. (a) Transmission spectrum of silicone oil measured at 1 atm. (b) Transmission spectrum of (BA)2(MA)2Pb3I10 sample in silicone oil at 1 atm. (c) Absorbance spectrum of (BA)2(MA)2Pb3I10 at 1 atm. (d) Tauc plot of (BA)2(MA)2Pb3I10 with a direct bandgap as 1.94 eV, which was obtained by fitting the linear portion of the plot and extracting at (αdhν)2=0.
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Fig. S4. Optical spectra and bandgap determination for (BA)2(MA)3Pb4I13 polycrystals at ambient. (a) Transmission spectrum of silicone oil measured at 1 atm. (b) Transmission spectrum of (BA)2(MA)3Pb4I13 sample in silicone oil at 1 atm. (c) Absorbance spectrum of (BA)2(MA)3Pb4I13 at 1 atm. (d) Tauc plot of (BA)2(MA)3Pb4I13 with a direct bandgap as 1.81 eV, which was obtained by fitting the linear portion of the plot and extracting at (αdhν)2=0.
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Fig. S5. Tauc plots and extrapolated bandgaps of (BA)2PbI4 under compression. Bandgaps obtained at 0.14 GPa (a), 0.71 GPa (b), 6.7 GPa (c) and 28.2 Gpa (d).
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Fig. S6. Tauc plots and extrapolated bandgaps of (BA)2(MA)2Pb3I10 under compression. Bandgaps obtained at 0.21 GPa (a), 1.9 GPa (b), 5.2 GPa (c) and 17.4 GPa (d).
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Fig. S7. Tauc plots and extrapolated bandgaps of (BA)2(MA)3Pb4I13 under compression. Bandgaps obtained at 0.2 GPa (a), 1.5 GPa (b), 4.7 GPa (c) and 13.1 GPa (d).
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Fig. S8. Contour plots of bandgaps with respect to pressure change. Left: (BA)2PbI4; Middle: (BA)2(MA)2Pb3I10; Right: (BA)2(MA)3Pb4I13.
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Fig. S9. Summary of the pressure-dependent bandgap evolutions on 2D perovskites. Purple: (BA)2PbI4; blue: (BA)2MAPb2I7; light green: (BA)2(MA)2Pb3I10; red: (BA)2(MA)3Pb4I13.
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Fig. S10. Proportions of inorganic layers in the total volume of perovskite unit cells. The volumetric content of inorganic fragment, 2L/D, monotonically decreases with smaller n (reduced dimensionality of perovskite material); L stands for the thickness of inorganic fragment, while D is the unit cell length of the longitudinal direction (c axes of (BA)2PbI4 and MAPbI3, b axes of (BA)2MAPb2I7, (BA)2(MA)2Pb3I10 and (BA)2(MA)3Pb4I13).1
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Fig. S11. Pressure-dependent structural evolutions on (BA)2PbI4. (a) XRD patterns as pressure increases from 0.12 GPa (blue) to 27 GPa (brown). (b) Lattice spacing of (004) (red), (111) (blue) and (110) (purple) planes, with respect to pressure change. (c) Normalized lattice spacings against the spacings at 5.9 GPa on (004) plane and amorphous structure. Clearly, amorphous structure (atomic distortions) shows a monotonic and almost linear decrease of lattice spacing as pressure increases beyond 5.9 GPa. Meanwhile, (004) plane exhibits a fluctuating change in lattice spacing from 5.9 to 27 GPa, and thus signifying the severe space compression.
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Fig. S12. Pressure-dependent structural evolutions on (BA)2(MA)2Pb3I10. (a) XRD patterns as pressure increases from 0.2 GPa (blue) to 27 GPa (orange). (b) Lattice spacing of (080) plane with respect to pressure change. A monotonic decrease in lattice spacing as pressure increases can be clearly viewed. (c) Normalized lattice spacings against the spacings at 4.5 GPa on (080) plane and amorphous structure.
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Fig. S13. Pressure-dependent structural evolutions on (BA)2(MA)3Pb4I13. (a) XRD patterns as pressure increases from 0.2 GPa (blue) to 24 GPa (dark brown). (b) Evolution of lattice spacing of (0100) plane with respect to pressure change. (c) Normalized lattice spacings against the spacings at 4.5 GPa on (0100) plane and amorphous structure.
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Fig. S14. Optical spectra and bandgap determination for (BA)2(MA)2Pb3I10 after decompression to 1 atm. (a) Transmission spectrum of silicone oil measured. (b) Transmission spectrum of (BA)2(MA)2Pb3I10 sample in silicone oil. (c) Absorbance spectrum of (BA)2(MA)2Pb3I10. (d) Tauc plot of (BA)2(MA)2Pb3I10 with a direct bandgap as 1.78 eV, which was obtained by fitting the linear portion of the plot and extracting at (αdhν)2=0.
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Fig. S15. Tauc plots of (BA)2(MA)2Pb3I10 during decompression. Tauc plots measured at 12.1 GPa (a), 9.2 GPa (b), 7.3 GPa (c), 4.2 GPa (d), 1.2 GPa (e) and 0.4 GPa (f), where bandgaps were respectively determined to be 1.85 eV, 2.04 eV, 2.12 eV, 2.36 eV, 2.55 eV and 1.99 eV.
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Fig. S16. Tauc plots of (BA)2PbI4 during decompression. Tauc plots measured at 12.2 GPa (a), 8.8 GPa (b) and 1.3 GPa (c) during the compression process, where bandgaps were respectively determined to be 1.85 eV, 1.82 eV and 2.14 eV.
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Fig. S17. Bandgap evolution of (BA)2PbI4 under compression and decompression. During decompression, (BA)2PbI4 bandgap monotonically increased as pressure was decreased from around 2 GPa to 1 atm, and it is nearly the same with the compression process. This bandgap evolution trend illustrates that no new energy route was created from pressure treatment process.
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Fig. S18. Refined XRD pattern of (BA)2PbI4 after decompression back to 1 atm. Distinctive diffraction peaks indicate the restored crystalline state of perovskite material, which has an orthorhombic structure with a Pbca space group and is almost unchanged when compared with the ambient structure before compression.2
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Fig. S19. Refined XRD pattern of (BA)2(MA)3Pb4I13 after decompression back to 1 atm. Broadened but still distinctive diffraction peaks indicate the reformed crystalline structure of perovskite material, which has an orthorhombic structure with a Pbca space group that is different from the structure before compression.1,3
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Fig. S20. Tauc plots of (BA)2(MA)3Pb4I13 during decompression. Tauc plots measured at 13.7 GPa (a), 9.6 GPa (b) and 5.0 GPa (c) during the compression process, where bandgaps were respectively determined to be 1.66 eV, 1.99 eV and 2.21 eV.
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Fig. S21. Bandgap evolution of (BA)2(MA)3Pb4I13 under compression and decompression. Different from the compression process, during decompression the bandgap increased up to 2.21 eV. Such bandgap evolution indicated a new recrystallization route with optimal energy pathways that are different from the compression process.
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Fig. S22. Pressure-dependent crystallinity evolution on (BA)2(MA)3Pb4I13. (a) XRD patterns of (BA)2(MA)3Pb4I13 at 24 GPa (red), 6.3 GPa (blue) and 3.3 GPa (orange) during decompression. Inset: diffraction pattern image measured at 6.3 GPa near the center detector position, where no diffraction spots or rings are found, and therefore indicates the amorphous state of perovskite material at this pressure condition. (b) Full width at half maximum (FWHM) of the diffraction peaks at around 12˚-13˚ of 2θ. During decompression, FWHM first increases from around 2.2˚ (24 GPa) to 2.9˚ (6.3 GPa), then decreases to around 2.1˚ (3.3 GPa), thereby corroborating the severe atomic distortion at 6.3 GPa.
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Fig. S23. Density of states (DOS) of (BA)2PbI4 with different Pb1-I2-Pb1 angles.
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Table S1. Crystal data and structure refinements of (BA)2(MA)2Pb3I10 polycrystals at ambient pressure condition (before compression and after decompression).
Before compression
After decompression
crystal system
orthorhombic, C2ab
orthorhombic, C2ab
unit cell dimensions
a = 8.9275(6) Å
a = 8.9514(25) Å
b = 51.959(4) Å
b = 50.277(16) Å
c = 8.8777(6) Å
c = 8.9483(4) Å
full-matrix least-squares on F2
full-matrix least-squares on F2
refinement method
Pb-I-Pb bond angles (degrees) Pb1-I1-Pb2
169.52(12)
170.58(5)
Pb2-I2-Pb2’
172.28(17)
172.98(10)
Pb2-I3-Pb2’
164.57(15)
167.18(6)
Pb1-I4-Pb1’
171.30(30)
172.04(4)
Pb1-I4
3.065(8)
3.142(1)
Pb1-I1
3.157(3)
3.058(1)
Pb1-I4’
3.249(8)
3.297(3)
Pb2-I5’
3.047(4)
2.812(2)
Pb2-I2
3.152(6)
3.244(1)
Pb2-I3
3.160(6)
3.149(2)
Pb2-I2’
3.170(6)
3.264(2)
Pb2-I3’
3.179(6)
3.245(3)
Pb-I bond lengths (Å)
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Table S2. Crystal data and structure refinements of (BA)2PbI4 polycrystals at ambient condition (before compression and after decompression).
Before compression
After decompression
crystal system
orthorhombic, Pbca
orthorhombic, Pbca
unit cell dimensions
a = 8.9302(5) Å
a = 8.9026(13) Å
b = 8.7673(5) Å
b = 8.7271(14) Å
c = 27.795(1) Å
c = 27.633(9) Å
full-matrix least-squares on F2
full-matrix least-squares on F2
refinement method
Pb-I-Pb bond angles (degrees) Pb1-I2-Pb1’
156.1(1)
156.0(3)
Pb1-I1
3.171(3)
3.181(5)
Pb1-I2
3.201(1)
3.221(4)
Pb1-I2’
3.194(2)
3.152(6)
Pb-I bond lengths (Å)
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Table S3. Crystal data and structure refinements of (BA)2(MA)3Pb4I13 polycrystals at ambient pressure condition (before compression and after decompression).
Before compression
After decompression
crystal system
orthorhombic, Cc2m
orthorhombic, Cc2m
unit cell dimensions
a = 8.9274(4) Å
a = 8.9868(25) Å
b = 64.383(3) Å
b = 62.361(19) Å
c = 8.8816(4) Å
c = 8.9343(4) Å
full-matrix least-squares on F2
full-matrix least-squares on F2
refinement method
Pb-I-Pb bond angles (degrees) Pb1-I2-Pb1’
168.8(14)
168.5(5)
Pb1-I3-Pb3
167.6(12)
167.9(10)
Pb1-I4-Pb2
167.2(6)
166.9(3)
Pb1-I6-Pb1’
172.4(12)
172.1(8)
Pb4-I9-Pb4’
172.9(14)
173.6(7)
Pb2-I1-Pb2’
166.1(12)
166.5(4)
Pb2-I5-Pb4
165.0(9)
165.5(3)
Pb2-I13-Pb2
172.7(14)
172.5(7)
Pb3-I8-Pb3’
170.4(14)
170.2(17)
Pb3-I12-Pb3’
165.5(13)
166.1(10)
Pb4-I7-Pb4’
162.6(14)
162.3(2)
Pb1-I4
3.120(20)
3.117(3)
Pb1-I3
3.140(20)
3.165(9)
Pb1-I6
3.154(8)
3.177(7)
Pb1-I2
3.164(8)
3.152(7)
Pb-I bond lengths (Å)
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Pb2-I5
3.122(17)
3.042(19)
Pb2-I13
3.156(8)
3.066(21)
Pb2-I1
3.170(8)
3.095(22)
Pb2-I4
3.260(20)
3.151(14)
Pb3-I10
3.060(20)
3.120(32)
Pb3-I8
3.161(8)
3.031(3)
Pb3-I12
3.172(9)
3.082(9)
Pb3-I3
3.270(20)
3.180(10)
Pb4-I11
3.010(20)
3.055(15)
Pb4-I9
3.164(8)
3.094(4)
Pb4-I7
3.175(9)
3.085(5)
Pb4-I5
3.330(15)
3.131(5)
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References 1. Stoumpos CC, Cao DH, Clark DJ, Young J, Rondinelli JM, Jang JI, Hupp JT, Kanatzidis MG (2016) Ruddlesden-Popper hybrid lead iodide perovskite 2D homologous semiconductors. Chem Mater 28:2852–2867. 2. Billing DG, Lemmerer A (2007) Synthesis, characterization and phase transitions in the inorganic-organic layered perovskite-type hybrids [(CnH2n+1NH3)2PbI4], n = 4, 5, and 6. Acta Cryst B 63:735–747. 3. Cao DH, Stoumpos CC, Farha OK, Hupp JT, Kanatzidis MG (2015) 2D homologous perovskites as light-absorbing materials for solar cell applications. J Am Chem Soc 137:7843–7850.
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