A Direct Bandgap Copper Antimony Halide Perovskite

Transcription

1 Supporting Information for: A Direct Bandgap Copper Antimony Halide Perovskite Brenda Vargas, a Estrella Ramos, a Enrique Pérez-Gutiérrez, b Juan Carlos Alonso a and Diego Solis-Ibarra a * ainstituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, CU, Coyoacán, 04510, Ciudad de México, México bconacyt-laboratorio de Polímeros, Centro de Química, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla (BUAP), Complejo de Ciencias, ICUAP, C.P Puebla, México. S1

2 Experimental Section General Considerations Reagents were purchased from commercial vendors and used as received. Solvents were of reagent grade or higher purity. All manipulations were conducted in air. Synthesis of Cs 4 CuSb 2 Cl 12 (1) Black polycrystalline Cs 4 CuSb 2 Cl 12 (1) was precipitated by adding g of CsCl (4.0 mmol) to a solution of Sb 2 O 3 (0.292 g, 2.0 mmol) and CuCl 2 (0.135 g, 1.0 mmol) in 4.0 ml of 36% HCl. The black precipitated was filtered on a glass frit and dried under reduced pressure to afford g (90.8% yield) of product. Crystals suitable for structure determination were obtained by heating a solution of 1 in concentrated HCl to 120 C in a pressure vessel. The solution was then slowly cool down to room temperature over the course of 24 hours. Synthesis of α-cs 3 Sb 2 Cl 9 (2) Polycrystalline α-cs 3 Sb 2 Cl 9 (2) was precipitated out of a solution of Sb 2 O 3 (0.292 g, 2.0 mmol) in 2.0 ml of 36% HCl by addition of g of CsCl (3.0 mmol). The colourless precipitated was filtered on a glass frit and dried under reduced pressure to afford g (86.5 % yield) of product. Material Characterization Powder X-Ray diffraction measurements were performed on a Rigaku Ultima IV diffractometer with Cu Kα radiation (l= Å) at 40 kv and 44 ma. The instrument was operating in a Bragg Brentano geometry with a step increment of 0.02 and an acquisition time of one second per step. Thermogravimetric analysis was performed with a TGA Q5000 V3.17 Build 265 (TA Instruments) in nitrogen (flow rate 10 ml/min) with a platinum pan at a heating rate of 5 C/min. The temperature range was from 25 to 500 ºC. Differential thermal analysis was S2

3 performed with a DSC Q2000 V24.11 Build 124 (TA Instruments) in a nitrogen atmosphere (flow rate 50 ml/min) with aluminum pan at a heating rate of 5 C/min. The temperature range was from 85 to 200 C. Absorption measurements were recorded using a Shimadzu spectrophotometer (UV- 2600) or an Agilent Cary 5000 UV-Vis-NIR. Both instruments were equipped with an integrated sphere and collected using diffuse reflectance data on a bulk powder sample. Optical band-gap determination The obtained reflectance spectra were converted to pseudo-absorbance spectra using the Kubelka-Munk transformation: 1 α = 1 R & 2R where R is the reflectance and α is the pseudo-absorbance. Then, a modified Kubelka- Munk function was obtained by multiplying α by the photon energy hν using the corresponding coefficient n associated with an electronic transition as: α hv + where n = 2 for direct transitions. Band gaps were extracted by fitting the linear regions of a plot of (α * hv) 2 vs E (where E = photon energy) and determining the x-intercept. Conductivity Studies A sample pellet was made from ca. 0.7 g of 1 uniaxially pressed into disk shaped pellets (1.34 cm in diameter and ca cm thick) under a pressure of 5.5 tons. The pellets were then polished to obtain planar surfaces. Silver paint (PELCO Leitsilber 200 Silver Paint) was brushed onto both sides of the disk-shaped pellets to serve as the electrode. Current-voltage curves were recorded with a voltage source Keithley 2400 SourceMeter previously calibrated. Electrical DC resistivity measurements were performed in air with S3

4 a voltage sweep from -1 V to 1 V in a setup with spring activated platinum wires pressed against the silver contacts. The setup was then introduced inside a furnace where measurements were made every 40 minutes in a temperature range of 40 C to 150 C in intervals of 10 C. DC resistivity (ρ) was calculated based on the geometrical size of the pellet as: ρ = R A/l where R is the resistance, A is the uniform cross-section of the sample and l is the thickness of the sample. The electrical conductivity (σ) can then be calculated as: σ=1/ ρ The relationship between electrical conductivity, activation energy and temperature is shown in the following expressions: σ= A[exp(-E a /2kT)] or ln σ = ln A - E a /2kT where σ is the electrical conductivity, A is representative of Arrhenius type activation energy (negligible temperature dependence), E a is the activation energy, k is the Boltzmann constant ant T is the absolute temperature in Kelvin. From the equations, it can be seen that the activation energy can be determined by the slope of a logarithmic plot of σ versus 1/2kT. S4

5 Photostability studies Simulated sun irradiation was carried using a 40W Oriel (Xe) lamp-illuminator (Newport-67005) as a light source. UV stability test were carried using a 7 W UV lamp (l max = 360 nm). Computational Details DFT calculations were carried using Dmol3 2,3, CASTEP 4 and the Vienna Ab initio Simulation Package (VASP) 5,6. Qualitatively, all three programs gave similar results (character of the bandgap and DOS/PDOS behavior for both, 1 and 2). However, Dmol3 results were the ones that better matched our experimental results (Table S1) and thus, are the ones used for analysis. Table S1. Bandgap values for 1 and 2 as determined by different methods Method Bandgap for 1 (ev) Bandgap for 2 (ev) Dmol CASTEP VASP Experimental Dmol3 electronic calculations (electronic band structure and total and partial density of states) were undertaken by applying the double-numeric quality basis set with polarization functions (dnp). We applied a global cutoff of 6.1 Å. The exchange correlation interaction was calculated with the generalized gradient approximation using the functional parameterized by Perdew, Burke, and Ernzerhof (PBE). 7 The convergence threshold for the self-consistent field was 10-6 Ha. The Brillouin zone has been sampled with a highly-converged set of k points, using grids up to (4x6x4) points according to the Monkhorst Pack scheme 8 for all calculations. The unit cells of (1) and (2) was taken from S5

6 their respective X-ray structures. Partial densities of states (pdos) were obtained considering the contribution of specific atoms onto the total density of states. The calculations realized with CASTEP, code was applied the Hubbard U parameter, for Cu atom (U dcu =2.5 ev), with PBE 6 functional and ultrasoft pseudopotentials. 9 We used a cutoff energy of 440 ev and a highly-converged k-point set according to the Monkhorst-Pack scheme 7 with grids of up to 4x6x4 k points. The convergence threshold for the self-consistent field was 10-6 Ha. The DFT-VASP 5,6 calculations were performed using projector augmented wave (PAW) potentials 11,12 and employed with the PBE 7 density functional. The PAW potentials are used to describe the core electrons as well as valence electrons. We used a cutoff energy of 300 ev and a highly-converged k-point set according to the Monkhorst- Pack scheme 7. The convergence threshold for the self-consistent field was 10-4 ev. Effective masses calculated for holes (m h = 0.16) and electrons (m e = 0.32) were calculated by parabolic fitting along the directions C (0,0.5,0.5)à Y (0,0.5,0). Values are given relative to the electron mass (m e ). Single Crystal X-ray Diffraction Studies (SCXRD) The single crystal X-ray diffraction studies of 1 was carried out on a Bruker Kappa APEX-II CCD diffractometer equipped with Mo K a radiation (l = Å). Crystals of the subject compound were grown by slow cooling a solution of 1 in concentrated HCl, the solution was cooled from 96 to 25 ºC over the course of 24 hours. A x x mm piece of a red block was mounted on a Cryoloop with Paratone oil. Data were collected in a nitrogen gas stream at 100(2) K using f and v scans. Crystal-todetector distance was 45 mm and exposure time was 8 seconds per frame using a scan width of Data collection was 99.8% complete to in q. A total of 7895 reflections were collected covering the indices, -16 <=h<=17, -9<=k<=9, -17<=l<=16. S6

7 1526 reflections were found to be symmetry independent, with a R int of Indexing and unit cell refinement indicated a C (face) center, monoclinic lattice. The space group was found to be C2/m. The data were integrated using the Bruker SAINT software program and scaled using the SADABS software program. 13 Solution by direct methods (SHELXT) produced a complete phasing model consistent with the proposed structure. 14,15 All atoms were refined anisotropically by full-matrix least-squares (SHELXL-2014). 14,15 Crystallographic data are summarized in Table S2. S7

8 Table S2. Crystal data and structure refinement for 1. Empirical formula Cs 4 CuSb 2 Cl 12 Formula weight Temperature 100 K Wavelength Å Crystal system Monoclinic Space group C2/m Unit cell dimensions a = (8) Å a= 90. b = (4) Å b= (3). c = (8) Å g = 90. Volume (12) Å 3 Z 2 Density (calculated) Mg/m 3 Absorption coefficient mm -1 F(000) 1110 Crystal size 0.2 x x mm 3 Crystal color, habit dark red block Theta range for data collection to Index ranges -16<=h<=17, -9<=k<=9, -17<=l<=16 Reflections collected 7895 Independent reflections 1526 [R(int) = ] Completeness to theta = % Absorption correction Semi-empirical from equivalents Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 1526 / 0 / 54 Goodness-of-fit on F Final R indices [I>2sigma(I)] R 1 = , wr 2 = R indices (all data) R 1 = , wr 2 = Extinction coefficient (4) Largest diff. peak and hole and e.å -3 S8

9 Figure S1. Photographs of microcrystalline samples of 1 (left) and 2 (right). Figure S2. Crystal Structure of 1 showing thermal ellipsoids at the 50% probability level as seen from b. Cl, Sb and Cu atoms are depicted as green, grey and blue ellipsoids respectively. Cesium atoms omitted for the sake of clarity. S9

10 Figure S3. Crystal Structure of 1 showing thermal ellipsoids at the 50% probability level as seen from the [111]-direction. Cl, Sb, Cu and Cs atoms are depicted as green, grey, blue and purple ellipsoids respectively. S10

11 Figure S4. Powder XRD patterns of Cs4CuSb2Cl12 (1, red) and the simulated powder pattern from the single-crystal structure of 1 (blue). Figure S5. Powder XRD patterns of α-cs3sb2cl9 (2, red) and the simulated powder pattern from the reported crystal structure of 2 (blue).16 S11

12 Figure S6. Absorbance spectrum of 2. Inset: Tauc plot for a direct bandgap semiconductor. Figure S7. Brillouin zone of 1. Green, purple, violet and orange represent chlorine, cesium, antimony and copper atoms respectively. The thick lines show the points of high symmetry in which the band diagram was evaluated. S12

13 Figure S8. Calculated band structure (left) and partial density of states (pdos, right) of 2. Occupied and empty bands are shown in blue and red respectively. Figure S9. Brillouin zone of 2. Green, purple and violet represent chlorine, cesium, and antimony atoms respectively. The thick lines show the points of high symmetry in which the band diagram was evaluated. S13

14 Figure S10. Stability of 1 towards humidity showing PXRD of 1 after exposure to 50 % relative humidity and 25 ºC at different times. Figure S11. PXRD of a sample 1 after 100-day exposure to 50% humidity (at 25ºC) shown in black and calculated PXRD pattern (red) from the single crystal structure. S14

15 Figure S12. Stability of 1 towards visible light and humidity showing PXRD of 1 after exposure to 50 % relative humidity and 25 ºC at different times. Figure S13. Stability of 1 towards UV light and humidity showing PXRD of 1 after constant exposure to UV light (380 nm) at 50 % relative humidity and 25 ºC. S15

16 References 1. Kubelka, P.; Munk, F. Z. Tech. Phys. 1931, 12, Delley, B; J. Chem. Phys. 1990, 92, Delley, B; J. Chem. Phys. 2000, 113, Clark S. J.; Segall M. D.; Pickard C. J.; Hasnip P. J.; Probert M. I. J.; Refson K.; Payne M.C.; Z. Krist. 2005, 220, Kresse, G.; J. Non-Cryst. Solids 1995, , Kresse, G.; Furthmüller, J.; Comp. Mater. Sci. 1996, 6, Perdew, J. P.; Burke, K; Ernzerhof, M.; Phys. Rev. Lett. 1996, 77, Monkhorst, H. J.; Pack, J.D.; Phys. Rev. B 1976, 13, Vanderbilt, D.; Phys. Rev. B, 1991, 41, Pfrommer B. G.; Côté, M; Louie, S.G.; Cohen, M. L.; J. Comp. Phys. 1997, 131, Blochl, P.E.; Phys. Rev. B, 1994, 50, Kresse, G.; Joubert, D.; Phys. Rev. B, 1990, 59, SAINT and SADABS; Bruker AXS Inc.: Madison, WI, (2007). 14. Sheldrick, G. M. SHELXL-97, Program for crystal structure refinement; Göttingen, G. M. Sheldrick, G. M. Acta Cryst. Sect. A 2008, 64, Kihara, K.; Sudo, T. Z. Kristallog. Krist. 1971, 134 (1-6), 142. S16