Efficient Planar Perovskite Solar Cells Based on 1.8-eV Bandgap ...
Supporting Information
Efficient Planar Perovskite Solar Cells Based on 1.8-eV Bandgap CH3NH3PbI2Br Nanosheets via Thermal Decomposition Yixin Zhaoa* and Kai Zhub* a
School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Rd., Shanghai 200240, China b
Chemical and Materials Science Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401 (USA)
Experimental: Fluorine-doped SnO2-coated transparent conducting glass substrate (FTO; TEC15, Hartford, USA) was pre-patterned by etching with Zn powder and 25 wt% HCl solution for about 1 min. The patterned FTO substrate was then cleaned by soaking in 5 wt% NaOH alcohol solution for 16 h followed by rinsing it sequentially with deionized (DI) water and ethanol. The cleaned FTO substrate was subsequently coated with a compact TiO2 layer by spray pyrolysis using 0.2 M Ti(IV) bis(ethyl acetoacetate)-diisopropoxide 1-butanol solution at 450°C, followed by annealing at 450°C for 1 h. CH3NH3Br (MABr) was synthesized by reacting methylamine (33 wt% ethanol solution) and hydrobromidic acid (47 wt% in water, Aldrich) with the molar ratio of 1.2:1 in an ice bath for 2 h with stirring followed by vacuum drying and cleaning with acetonitrile. CH3NH3Cl (MACl) was synthesized by reacting methylamine (33 wt% ethanol solution) and 33 wt% hydrocholoride acid with the molar ratio of 1.2:1 in an ice bath for 2 h with stirring followed by vacuum drying and cleaning with acetonitrile. 0.693 g PbI2 (1.5 mmol); 0.169 g MABr (1.5 mmol); and 0 g, 0.100 g (1.5 mmol), or 0.200 g (3 mmol) MACl were dissolved in 2.6 g dimethylformamide (DMF) at room temperature to form three different CH3NH3PbI2Br precursor solutions, denoted as PbI2+MABr, PbI2+MABr+MACl and PbI2+MABr+2MACl, S1
respectively. Devices were fabricated in ambient condition (unless stated otherwise) as detailed below. The perovskite CH3NH3PbI2Br precursors were spin-coated onto compact TiO2 films on TEC15 FTO at 2500 rpm for 10 s. The perovskite-coated films were then annealed on a hotplate at 125°C for about 5–40 min. The average thickness of the perovskite films is about 200–250 nm as determined by a surface profiler. 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 0.1 M 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9’-spirobifluorene (spiro-MeOTAD), 0.035
M
bis(trifluoromethane)sulfonimide
lithium
salt
(Li-TFSi),
and
0.12
M
4-tert-butylpyridine (tBP) in chlorobenzene/acetonitrile (10:1, v/v) solution. Finally, a 150-nm-thick Ag layer was deposited on the HTM layer by thermal evaporation. The active area of each device was about 0.25 cm2. The crystal structures of the perovskite films were measured by X-ray diffraction (XRD, Bruker D8 ADVANCE with Cu Kα radiation). The absorption spectra of the planar perovskite films were characterized by an UV/Vis spectrophotometer (Cary-60). The MACl, MABr, perovskite powders were analyzed by thermogravimetric analysis (TGA) with Mettler-Toledo TGA Instrument using a 5°C/min ramp up to 300 °C in N2 atmosphere with a steady flow rate of 10 mL/min. The powders of MAPbI2Br and PbI2•MABr•MACl were prepared by drying respectively the precursors of PbI2+MABr and PbI2+MABr+MACl at 70oC until forming the dry powders of black MAPbI2Br and yellow PbI2-MABr-MACl. The powders of MACl, MABr, PbI2-MABr and PbI2-MABr-MACl were first pre-TGA tested at 100oC until there is no weight loss to make sure all moisture and DMF residue were removed before the regular TGA measurement. The photocurrent–voltage (J–V) characteristic of perovskite CH3NH3PbI2Br solar cells were measured with a Keithley 2400 source meter under the simulated AM 1.5G illumination (100 mW/cm2; Oriel Sol3A Class AAA Solar Simulator). 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).
S2
Figure S1. Typical large-scale SEM image of MAPbI2Br film prepared from the PbI2+MABr+MACl precursor on a planar TiO2 compact layer on FTO substrate.
S3
Figure S2. UV-vis absorption spectra of perovskite MAPbI2Br on planar TiO2 films as a function of annealing time at 125oC using various precursors: (a) PbI2+MABr; (b) PbI2+MABr+MACl; and (c) PbI2+MABr+2MACl. The bandgap of these perovskite films is about 1.8 eV.
Table S1. Effect of Precursor Composition on Short-Circuit Photocurrent Density Jsc, Open-Circuit Voltage Voc, Fill Factor FF, and Conversion Efficiency η of Planar Perovskite MAPbI2Br Solar Cells. Precursor Jsc (mA/cm2) Voc (V) FF η (%) Composition PbI2+MABr
7.34
0.80
0.52
3.06
PbI2+MABr+MACl
14.81
1.09
0.62
10.03
PbI2+MABr+2MACl
14.30
0.98
0.58
8.04
S4
Figure S3. The incident photon-to-current efficiency (IPCE) of perovskite MAPbI2Br solar cell prepared from the PbI2+MABr+MACl precursor solution.
Figure S4. Effect of precursor composition on the recombination resistance (Rrec) as a function of voltage for planar perovskite MAPbI2Br solar cells.
S5
Figure S5. Effect of precursor composition on the dark J–V curves of planar perovskite MAPbI2Br solar cells.
Table S2. Effect of Precursor Composition and Annealing Time on the Pb:I:Br:Cl Ratio of Perovskite Films Time Precursor Pb I Br Cl (min)
a
PbI2+MABr
1
1
2.0 (0.2a)
1.1 (0.2)
−
PbI2+MABr+MACl
1 5 10 25
1 1 1 1
1.9 (0.2) 1.9 (0.2) 2.0 (0.2) 1.9 (0.2)
1.1 (0.2) 1.1 (0.2) 1.1 (0.2) 1.1 (0.2)
0.7 (0.1) 0.3 (0.1) 0.1 (0.1) −
PbI2+MABr+2MACl
40
1
2.0 (0.2)
1.1 (0.2)
−
The errors of the element ratios are obtained based on the EDX detection limit of 1%.
S6
Efficient Planar Perovskite Solar Cells Based on 1.8-eV Bandgap CH3NH3PbI2Br Nanosheets via Thermal Decomposition Yixin Zhaoa* and Kai Zhub* a
School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Rd., Shanghai 200240, China b
Chemical and Materials Science Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401 (USA)
Experimental: Fluorine-doped SnO2-coated transparent conducting glass substrate (FTO; TEC15, Hartford, USA) was pre-patterned by etching with Zn powder and 25 wt% HCl solution for about 1 min. The patterned FTO substrate was then cleaned by soaking in 5 wt% NaOH alcohol solution for 16 h followed by rinsing it sequentially with deionized (DI) water and ethanol. The cleaned FTO substrate was subsequently coated with a compact TiO2 layer by spray pyrolysis using 0.2 M Ti(IV) bis(ethyl acetoacetate)-diisopropoxide 1-butanol solution at 450°C, followed by annealing at 450°C for 1 h. CH3NH3Br (MABr) was synthesized by reacting methylamine (33 wt% ethanol solution) and hydrobromidic acid (47 wt% in water, Aldrich) with the molar ratio of 1.2:1 in an ice bath for 2 h with stirring followed by vacuum drying and cleaning with acetonitrile. CH3NH3Cl (MACl) was synthesized by reacting methylamine (33 wt% ethanol solution) and 33 wt% hydrocholoride acid with the molar ratio of 1.2:1 in an ice bath for 2 h with stirring followed by vacuum drying and cleaning with acetonitrile. 0.693 g PbI2 (1.5 mmol); 0.169 g MABr (1.5 mmol); and 0 g, 0.100 g (1.5 mmol), or 0.200 g (3 mmol) MACl were dissolved in 2.6 g dimethylformamide (DMF) at room temperature to form three different CH3NH3PbI2Br precursor solutions, denoted as PbI2+MABr, PbI2+MABr+MACl and PbI2+MABr+2MACl, S1
respectively. Devices were fabricated in ambient condition (unless stated otherwise) as detailed below. The perovskite CH3NH3PbI2Br precursors were spin-coated onto compact TiO2 films on TEC15 FTO at 2500 rpm for 10 s. The perovskite-coated films were then annealed on a hotplate at 125°C for about 5–40 min. The average thickness of the perovskite films is about 200–250 nm as determined by a surface profiler. 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 0.1 M 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9’-spirobifluorene (spiro-MeOTAD), 0.035
M
bis(trifluoromethane)sulfonimide
lithium
salt
(Li-TFSi),
and
0.12
M
4-tert-butylpyridine (tBP) in chlorobenzene/acetonitrile (10:1, v/v) solution. Finally, a 150-nm-thick Ag layer was deposited on the HTM layer by thermal evaporation. The active area of each device was about 0.25 cm2. The crystal structures of the perovskite films were measured by X-ray diffraction (XRD, Bruker D8 ADVANCE with Cu Kα radiation). The absorption spectra of the planar perovskite films were characterized by an UV/Vis spectrophotometer (Cary-60). The MACl, MABr, perovskite powders were analyzed by thermogravimetric analysis (TGA) with Mettler-Toledo TGA Instrument using a 5°C/min ramp up to 300 °C in N2 atmosphere with a steady flow rate of 10 mL/min. The powders of MAPbI2Br and PbI2•MABr•MACl were prepared by drying respectively the precursors of PbI2+MABr and PbI2+MABr+MACl at 70oC until forming the dry powders of black MAPbI2Br and yellow PbI2-MABr-MACl. The powders of MACl, MABr, PbI2-MABr and PbI2-MABr-MACl were first pre-TGA tested at 100oC until there is no weight loss to make sure all moisture and DMF residue were removed before the regular TGA measurement. The photocurrent–voltage (J–V) characteristic of perovskite CH3NH3PbI2Br solar cells were measured with a Keithley 2400 source meter under the simulated AM 1.5G illumination (100 mW/cm2; Oriel Sol3A Class AAA Solar Simulator). 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).
S2
Figure S1. Typical large-scale SEM image of MAPbI2Br film prepared from the PbI2+MABr+MACl precursor on a planar TiO2 compact layer on FTO substrate.
S3
Figure S2. UV-vis absorption spectra of perovskite MAPbI2Br on planar TiO2 films as a function of annealing time at 125oC using various precursors: (a) PbI2+MABr; (b) PbI2+MABr+MACl; and (c) PbI2+MABr+2MACl. The bandgap of these perovskite films is about 1.8 eV.
Table S1. Effect of Precursor Composition on Short-Circuit Photocurrent Density Jsc, Open-Circuit Voltage Voc, Fill Factor FF, and Conversion Efficiency η of Planar Perovskite MAPbI2Br Solar Cells. Precursor Jsc (mA/cm2) Voc (V) FF η (%) Composition PbI2+MABr
7.34
0.80
0.52
3.06
PbI2+MABr+MACl
14.81
1.09
0.62
10.03
PbI2+MABr+2MACl
14.30
0.98
0.58
8.04
S4
Figure S3. The incident photon-to-current efficiency (IPCE) of perovskite MAPbI2Br solar cell prepared from the PbI2+MABr+MACl precursor solution.
Figure S4. Effect of precursor composition on the recombination resistance (Rrec) as a function of voltage for planar perovskite MAPbI2Br solar cells.
S5
Figure S5. Effect of precursor composition on the dark J–V curves of planar perovskite MAPbI2Br solar cells.
Table S2. Effect of Precursor Composition and Annealing Time on the Pb:I:Br:Cl Ratio of Perovskite Films Time Precursor Pb I Br Cl (min)
a
PbI2+MABr
1
1
2.0 (0.2a)
1.1 (0.2)
−
PbI2+MABr+MACl
1 5 10 25
1 1 1 1
1.9 (0.2) 1.9 (0.2) 2.0 (0.2) 1.9 (0.2)
1.1 (0.2) 1.1 (0.2) 1.1 (0.2) 1.1 (0.2)
0.7 (0.1) 0.3 (0.1) 0.1 (0.1) −
PbI2+MABr+2MACl
40
1
2.0 (0.2)
1.1 (0.2)
−
The errors of the element ratios are obtained based on the EDX detection limit of 1%.
S6
