Supporting Information for Transition from Tetragonal to Cubic Phase
Supporting Information for Transition from Tetragonal to Cubic Phase of Organohalide Perovskite: The Role of Chlorine in Crystal Formation of CH 3NH 3PbI3 on TiO 2 Substrates Qiong Wanga, Miaoqiang Lyua, Meng Zhanga, Jung-Ho Yuna, Hongjun Chena, and Lianzhou Wanga*
a
Nanomaterials Centre, School of Chemical Engineering and Australian Institute for Bioengineering and Nanotechnology, the University of Queensland, St Lucia, QLD, 4072, Australia. Email: [email protected]
S1
Chemicals: Methylammonium iodide (CH3NH3I, Dyesol), lead iodide (PbI2, 99.999%, Alfa Aesar), lead chloride (PbCl 2, 99.999%, Sigma-Aldrich), N,N-dimethylformamide (DMF, anhydrous, Sigma-Aldrich), methylamine (33% in absolute ethanol, Aldrich), hydrochloric acid (ARC reagent, 37 wt% in water, Sigma-Aldrich). These chemicals were used as received. Experiments: Synthesis of methylammonium chloride (CH3NH3Cl): CH3NH3Cl was synthesized by modifying procedures described in reference. 1-2 More specifically, 33.7 ml of methylamine and 21.6 ml of hydrochloric acid were mixed in a round bottomed flask at room temperature, and then kept stirring for several hours. The precipitate was recovered using the vacuum rotary evaporator. The product, methylammonium chloride (CH3NH3Cl), was collected after several washings with diethyl ether, and then dried at 60 °C in vacuum oven. Precursor S1 was prepared by dissolving equal molar ratio of CH3NH3I and PbI2 at a concentration of 40 wt% in N,N-dimethylformamide (DMF) solvent. Perovskite S1 was prepared by spin-coating the solution at 2000 rpm/s for 60 seconds, and heated on a hot plate at 70 °C for 10 minutes. (Note: a longer annealing time or a higher annealing temperature makes the perovskite film change from dark brown to yellow, indicating decomposing of the perovskite layer into PbI 2.) Precursor S2 was prepared by dissolving additional amount of CH3NH3Cl in S1 under same molar ratio of CH3NH3I and PbI2. Perovskite S2 was prepared by spin-coating the solution at 2000 rpm/s for 60 seconds, and then annealed on a hot plate at 100 °C for 45 minutes. (Note: the annealing temperature and time adopts previous work3 to ensure the complete formation of perovskite layer) Precursor S3 was prepared by dissolving CH3NH3I and PbCl2 at a molar ratio of 3:1 with a total mass weight of 40 wt% in DMF solvent. Perovskite S3 was prepared under the same steps as that of perovskite S2. Precursor S4 was prepared by dissolving CH3NH3I and PbCl 2 at a molar ratio of 3:1 and a mass weight concentration of 60 wt% in DMF solvent. Perovskite S4 was prepared following the same procedure as perovskite S2 but the solution needs preheated at 70 °C before spin-
S2
coating due to the high viscosity of concentrated precursor solution S4. All annealing processes were conducted in air. Planar TiO 2 substrates were prepared by spin-coating TiO 2 sol-gel prepared following our previous method4 on top of fluorine-doped tin oxide (FTO) conductive glass, and then calcined at 450 ℃ for 30 min, resulting in a film thickness of around 140 nm. (XRD measurement and SEM of cross-sectional planar TiO 2 substrate is given in supporting material) TiO 2 mesoporous layer was deposited from diluted anatase TiO2 paste (Dyesol 30 NR-D diluted in absolute ethanol in mass ratio of 1 g to 5g) on top of planar TiO 2 substrates, and then calcined at 450 ℃ for 30 min. This gives a film thickness of around 300 nm. Thicker TiO 2 mesoporous layer was prepared by deposited another layer of TiO 2 mesoporous layer and calcined at 450 ℃ for 30 min again. This generates a film thickness of around 500 nm. Characterizations: The cross-sectional morphology of TiO 2 photoanodes was characterized by scanning electron microscopy (SEM, JEOL, JSM-7100F). X-ray diffraction (XRD) patterns were recorded on a Rigaku Miniflex with cobalt K α radiation. Results were then converted to copper target. The detection of chlorine in perovskite layer was measured using X-ray photoelectron spectroscopy (XPS, Kratos Axis Ultra photoelectron spectrometer with Al K α radiation). UVvis absorption spectra were collected with a V650 spectrophotometer (JASCO) with an integration sphere.
S3
S-Figure 1. Cross-sectional SEM images of a) planar TiO 2 substrate, b) TiO 2 mesoporous substrate of around 300 nm, c) TiO 2 mesoporous substrate of around 500 nm, d) Perovskite film deposited from S2 precursor on planar TiO 2 substrate with a thick capping layer of around 500 nm, e) Perovskite film deposited from S2 precursor on mesoporous TiO 2 substrate with a film thickness of around 300 nm and a capping layer of around 150 nm, and f) Perovskite film deposited from S2 precursor on mesoporous TiO 2 substrate with a film thickness of around 500 nm. The scale bar is 100 nm. a)
b)
c)
d)
e)
f)
S4
S-Figure 2 XPS measurement of CH 3NH 3PbI3 perovskite film deposited from chlorinecontained precursors, indicating no existence of chlorine at the surface of perovskite layer.
Atom% 50.62 37.73 11.65
C 1s
Pb 4f
CPS
I 3d
Name C 1s I 3d Pb 4f
700
600
500
400
300
Binding Energy (eV)
S5
200
100
S-Figure 3 XRD measurement of planar TiO 2 substrate, indicating anatase TiO 2 crystals.
S6
S-Figure 4 XRD results of CH 3NH 3PbI3 perovskite film deposited from S1 a) and S3 b) precursors on TiO 2 planar substrates (PS) and mesoporous substrates (MS) of around 500 nm. a) 100000
S1-PS 50000
0
S1-MS 10000
0
28.0
28.2
28.4 28.6 2 theta (degree)
28.8
29.0
b) 100000
S3-PS S3-MS
80000 60000 40000 20000 0 28.0
28.2
28.4
28.6
2 theta (degree)
S7
28.8
29.0
S-Figure 5 Absorbance spectra of CH 3NH 3PbI3 perovskite films deposited from S1, S2, and S3 on mesoporous TiO 2 (～300 nm) substrates.
1.0
Absorbance (a.u.)
0.8 0.6 0.4
S1 S2 S3
0.2 0.0 400
500
600
700
800
Wavelength (nm)
It shows that perovskite films exhibit different absorbance spectra in wavelength ranging from 400 nm to 750 nm, but they share same absorbance onset at around 780 nm. Therefore, the optical bandgaps of these samples should be very similar, around 1.59 eV, which are in consistent with published data.3, 5
S8
Reference: (1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 60506051. (2) Wang, Q.; Yun, J.-H.; Zhang, M.; Chen, H.; Chen, Z.-G.; Wang, L. Insight into The Liquid State of Organo-Lead Halide Perovskites and Their New Roles in Dye-Sensitized Solar Cells. J. Mater. Chem. A 2014, 2, 10355-10358. (3) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science 2012, 338, 643-647. (4) Wang, Q.; Butburee, T.; Wu, X.; Chen, H.; Liu, G.; Wang, L. Enhanced Performance of Dye-Sensitized Solar Cells by Doping Au Nanoparticles into Photoanodes: A Size Effect Study. J. Mater. Chem. A 2013, 1, 13524-13531. (5) Walsh, A. Principles of Chemical Bonding and Band Gap Engineering in Hybrid Organic–Inorganic Halide Perovskites. J. Phys. Chem. C 2015, 119, 5755-5760.
S9
a
Nanomaterials Centre, School of Chemical Engineering and Australian Institute for Bioengineering and Nanotechnology, the University of Queensland, St Lucia, QLD, 4072, Australia. Email: [email protected]
S1
Chemicals: Methylammonium iodide (CH3NH3I, Dyesol), lead iodide (PbI2, 99.999%, Alfa Aesar), lead chloride (PbCl 2, 99.999%, Sigma-Aldrich), N,N-dimethylformamide (DMF, anhydrous, Sigma-Aldrich), methylamine (33% in absolute ethanol, Aldrich), hydrochloric acid (ARC reagent, 37 wt% in water, Sigma-Aldrich). These chemicals were used as received. Experiments: Synthesis of methylammonium chloride (CH3NH3Cl): CH3NH3Cl was synthesized by modifying procedures described in reference. 1-2 More specifically, 33.7 ml of methylamine and 21.6 ml of hydrochloric acid were mixed in a round bottomed flask at room temperature, and then kept stirring for several hours. The precipitate was recovered using the vacuum rotary evaporator. The product, methylammonium chloride (CH3NH3Cl), was collected after several washings with diethyl ether, and then dried at 60 °C in vacuum oven. Precursor S1 was prepared by dissolving equal molar ratio of CH3NH3I and PbI2 at a concentration of 40 wt% in N,N-dimethylformamide (DMF) solvent. Perovskite S1 was prepared by spin-coating the solution at 2000 rpm/s for 60 seconds, and heated on a hot plate at 70 °C for 10 minutes. (Note: a longer annealing time or a higher annealing temperature makes the perovskite film change from dark brown to yellow, indicating decomposing of the perovskite layer into PbI 2.) Precursor S2 was prepared by dissolving additional amount of CH3NH3Cl in S1 under same molar ratio of CH3NH3I and PbI2. Perovskite S2 was prepared by spin-coating the solution at 2000 rpm/s for 60 seconds, and then annealed on a hot plate at 100 °C for 45 minutes. (Note: the annealing temperature and time adopts previous work3 to ensure the complete formation of perovskite layer) Precursor S3 was prepared by dissolving CH3NH3I and PbCl2 at a molar ratio of 3:1 with a total mass weight of 40 wt% in DMF solvent. Perovskite S3 was prepared under the same steps as that of perovskite S2. Precursor S4 was prepared by dissolving CH3NH3I and PbCl 2 at a molar ratio of 3:1 and a mass weight concentration of 60 wt% in DMF solvent. Perovskite S4 was prepared following the same procedure as perovskite S2 but the solution needs preheated at 70 °C before spin-
S2
coating due to the high viscosity of concentrated precursor solution S4. All annealing processes were conducted in air. Planar TiO 2 substrates were prepared by spin-coating TiO 2 sol-gel prepared following our previous method4 on top of fluorine-doped tin oxide (FTO) conductive glass, and then calcined at 450 ℃ for 30 min, resulting in a film thickness of around 140 nm. (XRD measurement and SEM of cross-sectional planar TiO 2 substrate is given in supporting material) TiO 2 mesoporous layer was deposited from diluted anatase TiO2 paste (Dyesol 30 NR-D diluted in absolute ethanol in mass ratio of 1 g to 5g) on top of planar TiO 2 substrates, and then calcined at 450 ℃ for 30 min. This gives a film thickness of around 300 nm. Thicker TiO 2 mesoporous layer was prepared by deposited another layer of TiO 2 mesoporous layer and calcined at 450 ℃ for 30 min again. This generates a film thickness of around 500 nm. Characterizations: The cross-sectional morphology of TiO 2 photoanodes was characterized by scanning electron microscopy (SEM, JEOL, JSM-7100F). X-ray diffraction (XRD) patterns were recorded on a Rigaku Miniflex with cobalt K α radiation. Results were then converted to copper target. The detection of chlorine in perovskite layer was measured using X-ray photoelectron spectroscopy (XPS, Kratos Axis Ultra photoelectron spectrometer with Al K α radiation). UVvis absorption spectra were collected with a V650 spectrophotometer (JASCO) with an integration sphere.
S3
S-Figure 1. Cross-sectional SEM images of a) planar TiO 2 substrate, b) TiO 2 mesoporous substrate of around 300 nm, c) TiO 2 mesoporous substrate of around 500 nm, d) Perovskite film deposited from S2 precursor on planar TiO 2 substrate with a thick capping layer of around 500 nm, e) Perovskite film deposited from S2 precursor on mesoporous TiO 2 substrate with a film thickness of around 300 nm and a capping layer of around 150 nm, and f) Perovskite film deposited from S2 precursor on mesoporous TiO 2 substrate with a film thickness of around 500 nm. The scale bar is 100 nm. a)
b)
c)
d)
e)
f)
S4
S-Figure 2 XPS measurement of CH 3NH 3PbI3 perovskite film deposited from chlorinecontained precursors, indicating no existence of chlorine at the surface of perovskite layer.
Atom% 50.62 37.73 11.65
C 1s
Pb 4f
CPS
I 3d
Name C 1s I 3d Pb 4f
700
600
500
400
300
Binding Energy (eV)
S5
200
100
S-Figure 3 XRD measurement of planar TiO 2 substrate, indicating anatase TiO 2 crystals.
S6
S-Figure 4 XRD results of CH 3NH 3PbI3 perovskite film deposited from S1 a) and S3 b) precursors on TiO 2 planar substrates (PS) and mesoporous substrates (MS) of around 500 nm. a) 100000
S1-PS 50000
0
S1-MS 10000
0
28.0
28.2
28.4 28.6 2 theta (degree)
28.8
29.0
b) 100000
S3-PS S3-MS
80000 60000 40000 20000 0 28.0
28.2
28.4
28.6
2 theta (degree)
S7
28.8
29.0
S-Figure 5 Absorbance spectra of CH 3NH 3PbI3 perovskite films deposited from S1, S2, and S3 on mesoporous TiO 2 (～300 nm) substrates.
1.0
Absorbance (a.u.)
0.8 0.6 0.4
S1 S2 S3
0.2 0.0 400
500
600
700
800
Wavelength (nm)
It shows that perovskite films exhibit different absorbance spectra in wavelength ranging from 400 nm to 750 nm, but they share same absorbance onset at around 780 nm. Therefore, the optical bandgaps of these samples should be very similar, around 1.59 eV, which are in consistent with published data.3, 5
S8
Reference: (1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 60506051. (2) Wang, Q.; Yun, J.-H.; Zhang, M.; Chen, H.; Chen, Z.-G.; Wang, L. Insight into The Liquid State of Organo-Lead Halide Perovskites and Their New Roles in Dye-Sensitized Solar Cells. J. Mater. Chem. A 2014, 2, 10355-10358. (3) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science 2012, 338, 643-647. (4) Wang, Q.; Butburee, T.; Wu, X.; Chen, H.; Liu, G.; Wang, L. Enhanced Performance of Dye-Sensitized Solar Cells by Doping Au Nanoparticles into Photoanodes: A Size Effect Study. J. Mater. Chem. A 2013, 1, 13524-13531. (5) Walsh, A. Principles of Chemical Bonding and Band Gap Engineering in Hybrid Organic–Inorganic Halide Perovskites. J. Phys. Chem. C 2015, 119, 5755-5760.
S9
