Supporting information

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1 Supporting information Confinement effects in low-dimensional lead iodide perovskite hybrids Machteld E. Kamminga 1, Hong-Hua Fang 1, Marina R. Filip 2, Feliciano Giustino 2, Jacob Baas 1, Graeme R. Blake 1, Maria Antonietta Loi 1, Thomas T.M. Palstra 1 1 Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands 2 Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom t.t.m.palstra@rug.nl S1

2 (PMA) 2 PbI 4 (PPA) 3 Pb 2 I 7 (PBA) 3 Pb 2 I 7 temperature (K) 100(2) 100(2) 100(2) formula (C 6 H 5 CH 2 NH 3 ) 2 PbI 4 [C 6 H 5 (CH 2 ) 3 NH 3 ] 3 Pb 2 I 7 [C 6 H 5 (CH 2 ) 4 NH 3 ] 3 Pb 2 I 7 formula weight (g/mol) crystal size (mm 3 ) 0.28 x 0.10 x x 0.14 x x 0.10 x 0.02 crystal color orange yellow yellow crystal system orthorhombic orthorhombic triclinic space group Pbca (no. 61) Pca2 1 (no. 29) P-1 (no. 2) symmetry centrosymmetric non-centrosymmetric centrosymmetric (polar) Z D (calculated) (g/cm 3 ) F(000) a (Å) (3) (8) (10) b (Å) (3) (3) (19) c (Å) (10) (3) (19) α ( ) (6) β ( ) (5) γ ( ) (6) volume (Å 3 ) (13) (14) (5) μ (mm -1 ) min / max transmission / / / θ range (degrees) index ranges -11 < h < < k < < l < < h < 9-37 < k < < l < < h < < k < < l < 20 data / restraints / 2287 / 0 / / 1 / / 5 / 323 parameters GooF of F no. total reflections no. unique reflections no. obs Fo > 4σ(Fo) R 1 [Fo > 4σ(Fo)] R 1 [all data] wr 2 [Fo > 4σ(Fo)] wr 2 [all data] largest peak and hole (e Å 3 ) 1.39 and and and Table S1. Crystallographic and refinement parameters of (PMA) 2 PbI 4, (PPA) 3 Pb 2 I 7 and (PBA) 3 Pb 2 I 7. All measurements are performed using Mo Kα radiation ( Å). Full-matrix least squares refinement against F 2 was carried out using anisotropic displacement parameters. Multi-scan absorption corrections were performed. Hydrogen atoms were added by assuming a regular tetrahedral coordination to carbon and nitrogen, with equal bond angles and fixed distances. For (PBA) 3 Pb 2 I 7, one of the three organic cations is particularly disordered. Therefore, the diffraction peaks are slightly S2

3 broadened, which lead to higher R-factors and did not enable us to refine this organic cation with anisotropic thermal factors. Figure S1. Asymmetric units of (a) (PMA) 2 PbI 4, (b) (PPA) 3 Pb 2 I 7 and (c) (PBA) 3 Pb 2 I 7 showing thermal ellipsoids of 50% probability. Note that all hydrogen atoms and one of the organic cations in (PBA) 3 Pb 2 I 7 are isotopically refined, as discussed in the caption of Table S1. S3

4 Temperature (K) a (Å) b (Å) c (Å) volume (Å 3 ) α = β = γ ( ) 100(2) (8) (3) (3) (14) (2) (3) (11) (11) (5) (2) 8.606(6) 30.49(2) 33.26(2) 8729(10) (2) (4) (16) (15) (7) 90.0 Table S2. Unit cell parameters of (PPA) 3 Pb 2 I 7, measured at different temperatures. The table shows that the overall volume of the unit cell increases with temperature, while the Pca2 1 space group is maintained. Larger quantities of the reaction products were analyzed for phase purity using powder XRD performed at room temperature after grinding in an agate mortar. In the case of (PPA) 3 Pb 2 I 7, most of the peaks in the diffraction pattern could be fitted using the 300K structural model obtained from single crystal XRD. A preferred orientation of the crystallites along the [001] direction was included in the model to obtain a better match to the measured peak intensities. However, several extra peaks from a second phase were also present, which by eye appeared to match the main peaks from a powder XRD pattern of PPA iodide salt. To the best of our knowledge the crystal structure of this salt has not been previously reported. In order to confirm the identity of the second phase, we first determined the unit cell of PPA iodide using the EXPO software 1. All peaks could be indexed in a triclinic unit cell; LeBail fitting was carried out to obtain the refined lattice parameters a = (7) Å, b = (5) Å, c = (3) Å, α = (4), β = (5), γ = (4). We were unable to solve the full structure of PPA iodide, thus this unit cell was added as a second phase to the Rietveld refinement of (PPA) 3 Pb 2 I 7 and LeBail fitting of the peak intensities was performed while keeping the lattice parameters fixed. The resulting fitted XRD profile is shown in Figure S2 (a). It is clear that the majority phase in the sample is (PPA) 3 Pb 2 I 7. While the structure of the inorganic part at 300K was solved, the structure of the organic part could not be determined reliably. Therefore the mismatches in intensity in the powder pattern are probably due to the inaccuracy in the configuration of the organic molecules at 300K. S4

5 For the (PBA) 3 Pb 2 I 7 sample, the diffraction pattern could be well fitted using the 300K atomic positions obtained from single crystal XRD, incorporating a preferred orientation model for crystallites aligned along [100]. Some relatively weak extra peaks could be fitted by adding the 4H polymorph of the starting material PbI 2 to the refinement as a second phase with a weight fraction of 4.8(2)%. 2 The fitted XRD profile is shown in Figure S2 (b). S5

6 Figure S2. Observed (black data points) and fitted (red line) powder XRD patterns of (a) (PPA) 3 Pb 2 I 7 reaction mixture and (b) (PBA) 3 Pb 2 I 7 reaction mixture. The lower row of tick marks in each case indicates the peak positions of the main hybrid phase. The upper row of tick marks indicates the peak positions of secondary phases: PPA iodide in (a) and lead iodide in (b). 10 Flow (mw/mg) 0 heating cooling Temperature (K) Figure S3. DSC data showing reversible first-order phase transitions at higher temperatures in (PBA) 3 Pb 2 I 7. S6

7 1, (PPA) 3 Pb 2 I 7 PL intensity (a.u.) 0, , (PEA) 2 PbI 4 (PMA) 2 PbI 4 (PBA) 3 Pb 2 I 7 0, Time (ps) Figure S4. Time-resolved photoluminescence spectra of (PMA) 2 PbI 4, (PEA) 2 PbI 4, (PPA) 3 Pb 2 I 7 and (PBA) 3 Pb 2 I 7. The decay of (PMA) 2 PbI 4 is fitted with a triexponential function with time constants of 37 ps (72.5%), 132 ps (26.1%) and 874 ps (1.4%). The decay of (PEA) 2 PbI 4, (PPA) 3 Pb 2 I 7 and (PBA) 3 Pb 2 I 7 are fitted with a biexponential function with time constants of 247 ps (71.6%) and 1127 ps (28.4%), 97 ps (19.4%) and 827 ps (80.6%), and 104 ps (94.8%) and 1200 ps (5.6%), respectively. References (1) Altomare, A.; Camalli, M.; Cuocci, C.; Giacovazzo, C. EXPO2009 : Structure Solution by Powder Data in Direct and Reciprocal Space. J. Appl. Cryst. 2009, 42, (2) Palosz, B.; Steurer, W.; Schulz, H. The Structure of PbI 2 Polytypes 2H and 4H: A Study of the 2H-4H Transition. J. Phys. Condens. Matter 1990, 2, S7