Lead-Free MA 2 CuCl x Br 4-x Hybrid Perovskites

Transcription

1 Supporting Information Lead-Free MA 2 CuCl x Br 4-x Hybrid Perovskites Daniele Cortecchia, 1,2 Herlina Arianita Dewi, 2 Jun Yin, 3 Annalisa Bruno, 2,3 Shi Chen, 3 Tom Baikie, 2 Pablo P. Boix, 2 Michael Grätzel, 4 Subodh Mhaisalkar, 2,5 Cesare Soci, 3 Nripan Mathews 2,5* 1 Interdisciplinary Graduate School, Energy Research Institute at NTU (ERI@N), Singapore Energy Research NTU (ERI@N), Research Technoplaza, Nanyang Technological University, Nanyang Drive, Singapore Division of Physics and Applied Physics, Nanyang Technological University, Singapore Laboratory of Photonics and Interfaces, Department of Chemistry and Chemical Engineering, Swiss Federal Institute of Technology, Station 6, CH Lausanne, Switzerland 5 School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, Singapore *Nripan@ntu.edu.sg S1

2 Sqrt(Counts) I. X-Ray diffraction pattern of MA 2 CuBr 4 and corresponding pawley fit: The Pawley fit of the powder X-Ray diffraction pattern of MA 2 CuBr 4 shows that its structure is consistent with the orthorhombic crystal system and space group Pbca. The refined lattice parametrs are: a = (9) ; b = (9) ; c = (4), with R B = The reflections indicated with a star (*) don t belong to the perovskite and indicate the presence of a secondary phase or impurities formed during the crystallization process ** * * hkl_phase 0.00 % MA 2 CuBr Th Degrees Figure S1 Pawley fit of the powder X-Ray diffraction pattern of MA 2 CuBr 4 : observed (blue) and calculated (red) diffraction pattern by Pawley fitting. The grey line is the difference between the observed and calculated pattern. S2

3 Sqrt(Counts) Sqrt(Counts) Sqrt(Counts) Sqrt(Counts) II. X-Ray diffraction pattern of MA 2 CuCl x Br 4-x and corresponding Pawley fit:pawley fits for the chlorine-stabilized copper perovskites MA 2 CuCl x Br 4-x a) hkl_phase 0.00 % MA 2 CuCl b) Th Degrees hkl_phase 0.00 % MA 2 CuCl 2 Br c) Th Degrees hkl_phase 0.00 % MA 2 CuClBr d) Th Degrees Th Degrees hkl_phase 0.00 % MA 2 CuCl 0.5 Br Figure S2 Pawley fit of the powder X-Ray diffraction pattern of the chlorine stabilized copper perovskite a) MA 2 CuCl 4 ; b) MA 2 CuCl 2 Br 2 ; c) MA 2 CuBr 3 and d) MA 2 Cu 0.5 Cl 3.5 : observed (blue) and calculated (red) diffraction pattern by Pawley fitting. The grey line is the difference between the observed and calculated pattern. S3

4 III. XRD study with increasing Br/Cl ratio: Due to the larger ionic radius of Br compared to Cl, the increase in Br/Cl ratio augments the unit cell dimensions, resulting in progressive peak shift to lower diffraction angles with Br addition from MA 2 CuCl 4 to MA 2 CuCl 0.5 Br 3.5 (Figure S3). Figure S3- Peak shift toward smaller diffraction angles upon increase of Br/Cl ratio. S4

5 IV. Thermogravimetric analysis (TGA): TGA of MA 2 CuCl 2 Br 2 and MA 2 CuCl 0.5 Br 3.5 are shown in Figure S4 a and b, respectively. The decomposition profile proceeds with two steps, and the first weight loss increases with higher Br content, indicating a major loss of Br compounds during this step, such as MABr and HBr, together with the release of MACl and HCl and CH 3 NH 2. At higher temperatures, the decomposition is possibly accompanied with the formation of higher boiling point compounds such as CuCl 2. Figure S4- TGA analysis for the compounds MA 2 CuCl 2 Br 2 and MA 2 CuCl 0.5 Br 3.5 S5

6 V. Annealing study: Annealing of MA 2 CuCl 0.5 Br 3.5 films at 100 C results in the loss of reflections characteristic of the perovskite structure, and extra reflections appear between 10 and 30 2θ (Figure S5). Samples annealed at 70 C for 30 min display residual MABr, which is minimized with prolonged annealing at 70 C for 1h. Figure S5 Effect of annealing temperature and time on the perovskite formation. S6

7 VI. Band Gap Determination: Tauc Plot construction for the determination of perovskite s direct band gap associated to CT transitions (Figure S6a) and schematic representation of the electronic transitions exemplified with the absorption spectrum of MA 2 CuCl 2 Br 2 (Figure S6b). Figure S6- a) Tauc plots for the determination of band-gaps associated to charge transfer (CT) transitions; b) representation of the electronic transitions for MA 2 CuCl 2 Br 2 : charge transfer transitions 1 and 2 (Cl, Br_pσ Cu_d x 2 y 2 and Cl, Br_pπ Cu_d x 2 y2 ) and d-d transition 3 (Cu_d xy Cu_d x 2 y 2). S7

8 VII. Low Temperature Absorption: Figure S7- Low temperature absorption measurement for a) MA 2 CuCl 4 and b) MA 2 CuClBr 3. Narrowing of the bands is observed at 78 K, together with blue-shift of the bandgap of about 20 nm and peak splitting of the main CT band. The observed behavior is in agreement with the thermochromism previously observed in similar compounds. 1 S8

9 VIII. X-Ray photoelectron spectroscopy (XPS): XPS analysis of MA 2 CuCl 2 Br 2, MA 2 CuCl 0.5 Br 3.5 and MA 2 CuBr 4 (Figure S8). In Cu 2p spectra, samples with chlorine show satellite peaks, indicating the presence of Cu 2+ ions. In pure bromine sample, the absence of a satellite peak suggest the surface of this sample changes to Cu +. Figure S8 XPS analysis of the series MA 2 CuCl x Br 4-x. S9

10 IX. Perovskite Band structure Figure S9 Electronic band structure from DFT simulation for a) MA 2 CuCl 2 Br 2 and b) MA 2 CuCl 0.5 Br 3.5. S10

11 X. Density of states based on DFT calculations: Projected density of states (PDOS) of the four copper pervoskite compounds (a) MA 2 CuCl 4, (b) MA 2 CuCl 2 Br 2, (c) MA 2 CuClBr 3, and (d) MA 2 CuCl 0.5 Br 3.5 from DFT calculations (Figure S10). Figure S10- PDOS for (a) MA 2 CuCl 4, (b) MA 2 CuCl 2 Br 2, (c) MA 2 CuClBr 3, and (d) MA 2 CuCl 0.5 Br 3.5 S11

12 XI. Cu-based d-d transitions: Figure S11- a) Details of Cu-based d-d transitions for MA 2 CuClBr 3 with 3-peaks fitting identifying the expected transitions a 1g (z 2 ) b 1g (x 2 y 2 ) ; b 2g (xy) b 1g (x 2 y 2 ) ; e g (xz, yz) b 1g (x 2 y 2 ) at cm -1, cm -1 and cm -1 respectively. b) energy level diagram for the d 9 electronic configuration in octahedral (O h ) and tetragonal (D 4h ) crystal field showing the effect of Jahn-Teller distortion on the energy level splitting. Based on the experimental values of the transitions, it is possible to define the value of 10Dq = cm - 1 and the splitting of e g levels due to Jahn-Teller stabilization D e = cm -1. The determined values are in excellent agreement with those reported in similar compounds. 2-3 S12

13 XII: SEM images of infiltration of TiO 2 with the Cu perovskite: SEM images of mesoporous TiO 2 infiltrated with MA 2 CuCl 2 Br 2 using DMSO solution of different concentration: 1M (a, c) and 2M (b, d) (Figure S12). Figure S12 SEM characterization for different concentrations of the spin coating solution for MA 2 CuCl 2 Br 2 S13

14 Currend Density [ A/cm 2 ] XIII. Dark Current of Mesoporous Solar Cells: MA 2 CuCl 2 Br 2 dark MA 2 CuCl 0.5 Br 3.5 dark Voltage [V] Figure S13 Dark current of mesoporous solar cells sensitized with MA 2 CuCl 2 Br 2 and MA 2 CuCl 0.5 Br 3.5 showing the rectifying behavior of the cells under dark condition. S14

15 XIV. Binding Energy and Work Function determination: Binding energy (BE) and work function (WF) determination for MA 2 CuCl 2 Br 2 and MA 2 CuCl 0.5 Br 3.5 by ultraviolet photoelectron spectroscopy (UPS). Figure S14 UPS analysis for MA 2 CuCl 2 Br 2 and MA 2 CuCl 0.5 Br 3.5 S15

16 XV. Impedance analysis of the Cu perovskite: Figure S15 - a) Example impedance spectra under 1 sun at 0.25 V for both analyzed samples, the inset represents the equivalent circuit employed for the fitting. b) Series resistance extracted from the fitting of the impedance spectrum measured under 1 sun. S16

17 XVI. Inverted solar cell: Copper perovskite-based solar cell with inverted structure PEDOT:PSS/ MA 2 CuCl 2 Br 2 /PCBM (Figure S16). Figure S16 IV curves for a flat-junction solar cell based on MA 2 CuCl 2 Br 2 as light harvester. References (1) Bloomquist, D. R.; Pressprich, M. R.; Willett, R. D. J. Am. Chem. Soc. 1988, 110, (2) Valiente, R.; Rodríguez, F. Phys. Rev. B 1999, 60, (3) Jaffe, A.; Lin, Y.; Mao, W. L.; Karunadasa, H. I. J. Am. Chem. Soc. 2015, 137, S17