Supporting Information Controllable Sequential Deposition of Planar
Supporting Information Controllable Sequential Deposition of Planar CH3NH3PbI3 Perovskite Films via Adjustable Volume Expansion Taiyang Zhang,a± Mengjin Yang,b± Yixin Zhao,a* Kai Zhub* a
Taiyang Zhang and Professor Yixin Zhao: School of Environmental Science and Engineering, Shanghai
Jiao Tong University, 800 Dongchuan Rd., Shanghai 200240, China; E-mail: [email protected] b
Dr. Mengjin Yang and Dr. Kai Zhu: Chemical and Materials Science Center, National Renewable
Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA; E-mail: [email protected] ±
These two authors contributed to this work equally.
Experimental Precursor Preparation: CH3NH3I (MAI) was synthesized by reacting methylamine (33 wt% ethanol solution) and hydroiodic acid (57 wt% in water, Aldrich) and purified as previously reported.1 Unless otherwise stated, the mixtures of 0.784 g PbI2 (1.7 mmol) and 0 g, 0.027 g (0.17 mmol), 0.041 g (0.26 mmol), 0.054 g (0.34 mmol), or 0.081 g MAI (0.51 mmol) were dissolved in 2 mL dimethylformamide (DMF) at room temperature to form five different precursor solutions with mixed PbI2 and MAI with a molar ratio of 1:x—noted as PbI2·xMAI (x=0, 0.1, 0.15, 0.2, 0.3, respectively). Device Fabrication: A patterned fluorine-doped tin oxide (FTO) was first deposited with a blocking layer by spray pyrolysis at 450oC using 0.2 M Ti(IV) bis(ethyl acetoacetate)-diisopropoxide 1-butanol solution, followed by 450oC annealing in air for one hour. The different PbI2·xMAI films were normally prepared by spin coating different PbI2·xMAI precursor solutions (pre-warmed at 65°C) onto the substrate at 65°C at 6000 rpm for 15 s. The spin-coated PbI2·xMAI films were dried in air before dipping in the 10 mg/mL MAI solution and keeping at 55°C in an oven for different durations. After quickly rinsing by anhydrous IPA twice, the MAPbI3 perovskite films were then annealed on a hotplate at 150°C for about 1 min, and then washed again by spin coating IPA at 4000 rpm for 15 s, followed by an additional annealing at 150oC for 1 min. A hole-transport material (HTM) solution was spin-coated on the perovskite-covered TiO2 electrodes at 4000 rpm for 30 s. The HTM solution consists of 0.065 M spiro-MeOTAD, 0.053 M bis(trifluoromethane)sulfonimide lithium salt (Li-TFSi), and 0.20 M 1
4-tert-butylpyridine (tBP) in chlorobenzene/acetonitrile (30:1, v/v) solution. Finally, a 150-nm-thick Ag layer was deposited on the HTM layer by thermal evaporation. A typical cell area was about 0.12 cm2 as defined by a shadow mask. Characterization: The crystal structures of the perovskite films were characterized by X-ray diffraction (XRD, Shimadzu XRD-6100 diffractometer with Cu Kα radiation). The morphologies of the perovskite films were examined on a FEI Sirion 200 scanning electron microscope (SEM). The optical absorption spectra of MAPbI3 perovskite films were measured by a UV/vis spectrophotometer (Cary-60). The photocurrent–voltage (J–V) characteristic and continuous power output of perovskite MAPbI3 solar cells were measured respectively with a Keithley 2400 source meter and a potentiostat (Princeton Applied Research, VersaSTAT MC) under the simulated AM 1.5G illumination (100 mW/cm2; Oriel Sol3A Class AAA Solar Simulator). Film thickness was measured by a surface profilometer (Dektak 8). Impedance spectroscopy (IS) was done using a PARSTAT 2273 workstation with the frequency range of 0.1 Hz–100 kHz and the modulation amplitude of 10 mV. The IS spectra were analyzed using ZView 2.9c software (Scribner Associates).
Figure S1. The SEM image of a perovskite MAPbI3 film with 6-min dipping (reaction) time in the IPA solution of MAI.
2
Figure S2. Typical J–V curves of planar MAPbI3 solar cells prepared from PbI2 precursor films with different MAI solution-dipping times from 0.5 to 20 min.
Table S1. Device parameters of planar MAPbI3 solar cells prepared from PbI2 precursor films. PbI2 in MAI time (min)
Jsc (mA/cm2)
Voc (V)
FF
0.5
6.54
0.979
0.491
3.15
2 6
8.85 15.52
0.969 0.961
0.712 0.624
6.11 9.30
20
4.51
0.489
0.584
1.29
η (%)
3
Figure S3. XRD patterns of PbI2·xMAI (x: 0.1–0.3) films after dipping in MAI solution for 1–3 min.
Table S2. Effect of PbI2·xMAI precursor composition (x: 0–0.3) on the device parameters of typical planar perovskite MAPbI3 solar cells using two-step sequential deposition. The mean values and standard deviations of the device parameters from about 8 to 16 cells for each type of devices are given in parentheses. Precursor Type
Jsc (mA/cm2)
Voc (V)
FF
η (%)
PbI2
8.85 (9.07±0.79)
0.969 (0.995±0.036)
0.712 (0.657±0.069)
6.11 (5.91±0.48)
PbI2+0.1MAI
17.07 (18.01±1.60)
1.089 (1.097±0.013)
0.726 (0.714±0.039)
13.49 (14.09±1.21)
PbI2+0.15MAI
19.89 (20.42±0.84)
1.065 (1.086±0.010)
0.738 (0.714±0.027)
15.62 (15.85±0.73)
PbI2+0.2MAI
18.37 (18.53±0.79)
1.041 (1.056±0.020)
0.729 (0.721±0.063)
13.93 (14.26±1.25)
PbI2+0.3MAI
13.87 (14.01±1.30)
0.967 (0.949±0.024)
0.668 (0.642±0.034)
8.98 (8.52±0.71)
4
Figure S4. (a) Typical Nyquist plots of the impedance responses for a typical perovskite cell with
three different bias voltages. The impedance spectra are dominated by a large semicircle at low frequencies. The model used for impedance analysis has been previously discussed in detail.2, 3 (b) Plots of recombination resistance Rrec as a function of voltage for solar cells prepared with different PbI2·xMAI precursor composition (x: 0–0.3).
Figure S5. (a) The J–V curve of a planar MAPbI3 solar cell prepared from PbI2·0.15MAI precursor with the highest efficiency of 17.22% (Jsc=21.12 mA/cm2, Voc=1.096 V, FF=0.744) under reverse/backward voltage scan at simulated one-sun illumination. The cell shows hysteresis with an efficiency of 14.01% under forward voltage scan. (b) Stability of power conversion efficiency as a function of time for the same cell in (a) under simulated one-sun illumination. (c) The external quantum efficiency (EQE) spectrum. The Jsc value is consistent with the EQE spectrum. It is worth to mention that there are reports showing that the integrated current density from EQE doesn’t always match well with Jsc from J-V measurement, which is presumably related to the difference in device characteristics (e.g., stability during measurement) for solar cells made under different conditions.4, 5 5
Table S3. The thickness of PbI2·xMAI film before and after the second conversion step. x MAI
Thickness of PbI2·xMAI (nm)
Thickness of CH3NH3PbI3 (nm)
0 0.1 0.15 0.2 0.3
119±5 nm 132±5 nm 144±6 nm 152±10 nm 179±11 nm
247±7 nm 242±8 nm 257±5 nm 251±9 nm 261±13 nm
Assuming the pre-expansion ratio per formula of reactant MAI and the expansion ratio in the standard conversion process with pure PbI2 are the same (denoted by m), the molar amount of PbI2 is 1, and the thickness of pure PbI2 film is d0, we can write the respective thicknesses of the initial PbI2·xMAI film (di) and the final MAPbI3 film (df) as di = mxd0 + (1–x)d0 = [1 + (m – 1)x]d0 (S1) (S2) df = md0 Thus, the ratio of df/di can be derived as df/di = m/[1 + (m – 1)x] (S3)
Table S4. Effect of PbI2·xMAI precursor composition (x: 0–0.3) on the Pb:I ratio of PbI2·xMAI films based on energy dispersive X-ray (EDX) analysis. x MAI 0 0.1 0.15 0.2 0.3
Pb 1 1 1 1 1
I 2.01 2.12 2.17 2.23 2.32
6
Figure S6. The J–V curve of a planar MAPbI3 solar cell prepared from about 350-nm-thick perovskite film using PbI2·0.15MAI precursor with the highest efficiency of 13.17% (Jsc=19.32 mA/cm2, Voc=1.04 V, FF=0.653) under simulated one-sun illumination. The cell performance level based on 350-nm perovskite layer is lower in comparison to the typical 250-nm perovskite cells in this study. A systematic study to further optimize the processing conditions for thicker perovskite films could lead to improved cell performance.
Figure S7. Surface profiler measurement of a typical 250-nm-thick perovskite thin film. 7
Figure S8. Comparison of XRD patterns of MAPbI3 and MAI.
References 1. 2. 3. 4. 5.
Y. Zhao and K. Zhu, J. Phys. Chem. Lett., 2013, 4, 2880-2884. E. J. Juarez-Perez, M. Wuβler, F. Fabregat-Santiago, K. Lakus-Wollny, E. Mankel, T. Mayer, W. Jaegermann and I. Mora-Sero, J. Phys. Chem. Lett., 2014, 5, 680-685. J. A. Christians, R. C. M. Fung and P. V. Kamat, J. Am. Chem. Soc., 2013, 136, 758-764. E. L. Unger, E. T. Hoke, C. D. Bailie, W. H. Nguyen, A. R. Bowring, T. Heumuller, M. G. Christoforo and M. D. McGehee, Energy Environ. Sci., 2014, 7, 3690-3698. J. M. Ball, S. D. Stranks, M. T. Horantner, S. Huttner, W. Zhang, E. J. W. Crossland, I. Ramirez, M. Riede, M. B. Johnston, R. H. Friend and H. J. Snaith, Energy Environ. Sci., 2015, 8, 602-609.
8
Taiyang Zhang and Professor Yixin Zhao: School of Environmental Science and Engineering, Shanghai
Jiao Tong University, 800 Dongchuan Rd., Shanghai 200240, China; E-mail: [email protected] b
Dr. Mengjin Yang and Dr. Kai Zhu: Chemical and Materials Science Center, National Renewable
Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA; E-mail: [email protected] ±
These two authors contributed to this work equally.
Experimental Precursor Preparation: CH3NH3I (MAI) was synthesized by reacting methylamine (33 wt% ethanol solution) and hydroiodic acid (57 wt% in water, Aldrich) and purified as previously reported.1 Unless otherwise stated, the mixtures of 0.784 g PbI2 (1.7 mmol) and 0 g, 0.027 g (0.17 mmol), 0.041 g (0.26 mmol), 0.054 g (0.34 mmol), or 0.081 g MAI (0.51 mmol) were dissolved in 2 mL dimethylformamide (DMF) at room temperature to form five different precursor solutions with mixed PbI2 and MAI with a molar ratio of 1:x—noted as PbI2·xMAI (x=0, 0.1, 0.15, 0.2, 0.3, respectively). Device Fabrication: A patterned fluorine-doped tin oxide (FTO) was first deposited with a blocking layer by spray pyrolysis at 450oC using 0.2 M Ti(IV) bis(ethyl acetoacetate)-diisopropoxide 1-butanol solution, followed by 450oC annealing in air for one hour. The different PbI2·xMAI films were normally prepared by spin coating different PbI2·xMAI precursor solutions (pre-warmed at 65°C) onto the substrate at 65°C at 6000 rpm for 15 s. The spin-coated PbI2·xMAI films were dried in air before dipping in the 10 mg/mL MAI solution and keeping at 55°C in an oven for different durations. After quickly rinsing by anhydrous IPA twice, the MAPbI3 perovskite films were then annealed on a hotplate at 150°C for about 1 min, and then washed again by spin coating IPA at 4000 rpm for 15 s, followed by an additional annealing at 150oC for 1 min. A hole-transport material (HTM) solution was spin-coated on the perovskite-covered TiO2 electrodes at 4000 rpm for 30 s. The HTM solution consists of 0.065 M spiro-MeOTAD, 0.053 M bis(trifluoromethane)sulfonimide lithium salt (Li-TFSi), and 0.20 M 1
4-tert-butylpyridine (tBP) in chlorobenzene/acetonitrile (30:1, v/v) solution. Finally, a 150-nm-thick Ag layer was deposited on the HTM layer by thermal evaporation. A typical cell area was about 0.12 cm2 as defined by a shadow mask. Characterization: The crystal structures of the perovskite films were characterized by X-ray diffraction (XRD, Shimadzu XRD-6100 diffractometer with Cu Kα radiation). The morphologies of the perovskite films were examined on a FEI Sirion 200 scanning electron microscope (SEM). The optical absorption spectra of MAPbI3 perovskite films were measured by a UV/vis spectrophotometer (Cary-60). The photocurrent–voltage (J–V) characteristic and continuous power output of perovskite MAPbI3 solar cells were measured respectively with a Keithley 2400 source meter and a potentiostat (Princeton Applied Research, VersaSTAT MC) under the simulated AM 1.5G illumination (100 mW/cm2; Oriel Sol3A Class AAA Solar Simulator). Film thickness was measured by a surface profilometer (Dektak 8). Impedance spectroscopy (IS) was done using a PARSTAT 2273 workstation with the frequency range of 0.1 Hz–100 kHz and the modulation amplitude of 10 mV. The IS spectra were analyzed using ZView 2.9c software (Scribner Associates).
Figure S1. The SEM image of a perovskite MAPbI3 film with 6-min dipping (reaction) time in the IPA solution of MAI.
2
Figure S2. Typical J–V curves of planar MAPbI3 solar cells prepared from PbI2 precursor films with different MAI solution-dipping times from 0.5 to 20 min.
Table S1. Device parameters of planar MAPbI3 solar cells prepared from PbI2 precursor films. PbI2 in MAI time (min)
Jsc (mA/cm2)
Voc (V)
FF
0.5
6.54
0.979
0.491
3.15
2 6
8.85 15.52
0.969 0.961
0.712 0.624
6.11 9.30
20
4.51
0.489
0.584
1.29
η (%)
3
Figure S3. XRD patterns of PbI2·xMAI (x: 0.1–0.3) films after dipping in MAI solution for 1–3 min.
Table S2. Effect of PbI2·xMAI precursor composition (x: 0–0.3) on the device parameters of typical planar perovskite MAPbI3 solar cells using two-step sequential deposition. The mean values and standard deviations of the device parameters from about 8 to 16 cells for each type of devices are given in parentheses. Precursor Type
Jsc (mA/cm2)
Voc (V)
FF
η (%)
PbI2
8.85 (9.07±0.79)
0.969 (0.995±0.036)
0.712 (0.657±0.069)
6.11 (5.91±0.48)
PbI2+0.1MAI
17.07 (18.01±1.60)
1.089 (1.097±0.013)
0.726 (0.714±0.039)
13.49 (14.09±1.21)
PbI2+0.15MAI
19.89 (20.42±0.84)
1.065 (1.086±0.010)
0.738 (0.714±0.027)
15.62 (15.85±0.73)
PbI2+0.2MAI
18.37 (18.53±0.79)
1.041 (1.056±0.020)
0.729 (0.721±0.063)
13.93 (14.26±1.25)
PbI2+0.3MAI
13.87 (14.01±1.30)
0.967 (0.949±0.024)
0.668 (0.642±0.034)
8.98 (8.52±0.71)
4
Figure S4. (a) Typical Nyquist plots of the impedance responses for a typical perovskite cell with
three different bias voltages. The impedance spectra are dominated by a large semicircle at low frequencies. The model used for impedance analysis has been previously discussed in detail.2, 3 (b) Plots of recombination resistance Rrec as a function of voltage for solar cells prepared with different PbI2·xMAI precursor composition (x: 0–0.3).
Figure S5. (a) The J–V curve of a planar MAPbI3 solar cell prepared from PbI2·0.15MAI precursor with the highest efficiency of 17.22% (Jsc=21.12 mA/cm2, Voc=1.096 V, FF=0.744) under reverse/backward voltage scan at simulated one-sun illumination. The cell shows hysteresis with an efficiency of 14.01% under forward voltage scan. (b) Stability of power conversion efficiency as a function of time for the same cell in (a) under simulated one-sun illumination. (c) The external quantum efficiency (EQE) spectrum. The Jsc value is consistent with the EQE spectrum. It is worth to mention that there are reports showing that the integrated current density from EQE doesn’t always match well with Jsc from J-V measurement, which is presumably related to the difference in device characteristics (e.g., stability during measurement) for solar cells made under different conditions.4, 5 5
Table S3. The thickness of PbI2·xMAI film before and after the second conversion step. x MAI
Thickness of PbI2·xMAI (nm)
Thickness of CH3NH3PbI3 (nm)
0 0.1 0.15 0.2 0.3
119±5 nm 132±5 nm 144±6 nm 152±10 nm 179±11 nm
247±7 nm 242±8 nm 257±5 nm 251±9 nm 261±13 nm
Assuming the pre-expansion ratio per formula of reactant MAI and the expansion ratio in the standard conversion process with pure PbI2 are the same (denoted by m), the molar amount of PbI2 is 1, and the thickness of pure PbI2 film is d0, we can write the respective thicknesses of the initial PbI2·xMAI film (di) and the final MAPbI3 film (df) as di = mxd0 + (1–x)d0 = [1 + (m – 1)x]d0 (S1) (S2) df = md0 Thus, the ratio of df/di can be derived as df/di = m/[1 + (m – 1)x] (S3)
Table S4. Effect of PbI2·xMAI precursor composition (x: 0–0.3) on the Pb:I ratio of PbI2·xMAI films based on energy dispersive X-ray (EDX) analysis. x MAI 0 0.1 0.15 0.2 0.3
Pb 1 1 1 1 1
I 2.01 2.12 2.17 2.23 2.32
6
Figure S6. The J–V curve of a planar MAPbI3 solar cell prepared from about 350-nm-thick perovskite film using PbI2·0.15MAI precursor with the highest efficiency of 13.17% (Jsc=19.32 mA/cm2, Voc=1.04 V, FF=0.653) under simulated one-sun illumination. The cell performance level based on 350-nm perovskite layer is lower in comparison to the typical 250-nm perovskite cells in this study. A systematic study to further optimize the processing conditions for thicker perovskite films could lead to improved cell performance.
Figure S7. Surface profiler measurement of a typical 250-nm-thick perovskite thin film. 7
Figure S8. Comparison of XRD patterns of MAPbI3 and MAI.
References 1. 2. 3. 4. 5.
Y. Zhao and K. Zhu, J. Phys. Chem. Lett., 2013, 4, 2880-2884. E. J. Juarez-Perez, M. Wuβler, F. Fabregat-Santiago, K. Lakus-Wollny, E. Mankel, T. Mayer, W. Jaegermann and I. Mora-Sero, J. Phys. Chem. Lett., 2014, 5, 680-685. J. A. Christians, R. C. M. Fung and P. V. Kamat, J. Am. Chem. Soc., 2013, 136, 758-764. E. L. Unger, E. T. Hoke, C. D. Bailie, W. H. Nguyen, A. R. Bowring, T. Heumuller, M. G. Christoforo and M. D. McGehee, Energy Environ. Sci., 2014, 7, 3690-3698. J. M. Ball, S. D. Stranks, M. T. Horantner, S. Huttner, W. Zhang, E. J. W. Crossland, I. Ramirez, M. Riede, M. B. Johnston, R. H. Friend and H. J. Snaith, Energy Environ. Sci., 2015, 8, 602-609.
8
