Supporting Information Thermally Stable Mesoporous Perovskite Solar ...
Supporting Information
Thermally Stable Mesoporous Perovskite Solar Cells incorporating Low-Temperature Processed Graphene/Polymer Electron Transporting Layer Shi Wun Tong, Janardhan Balapanuru, Deyi Fu and Kian Ping Loh* *Department of Chemistry and Centre for Advanced 2D Materials, National University of Singapore, 3 Science Drive 3, Singapore 119260 *Corresponding Author: [email protected] Contents Figure S1. Preparation routes of mesoporous graphene (mp-GP) film deposited on ITO substrate. Figure S2. (a) XRD spectra of rGO, PANI and mp-GP films. (b) Under different loading of rGO, the intensity and the FWHM of (020) XRD peak inside mp-GP composite. Figure S3. The optical bandgap of perovskite coated on mp-GP scaffold. Figure S4. SEM images of perovskite grown on mp-GP scaffolds with 0.2, 0.5 and 1wt% of rGO loading. Figure S5. Comparison of energy level alignment at the interfaces of perovskite/OMeTAD and perovskite/PffBT4T-2OD. Figure S6. UPS spectra of Cs2CO3 coated mp-GP and mp-GP scaffolds. Figure S7. AFM images of perovskite grown on Cs2CO3 coated mp-GP and mp-GP scaffolds. Figure S8. Optical absorption property of perovskite grown on Cs2CO3 coated mp-GP and mp-GP scaffolds. Figure S9. Electron mobility measurement of mp-GP scaffold with 1wt % rGO using the space-charge limited current of device. Figure S10. Four-point probes measurement of rGO, polyaniline, TiO2 and ZnO thin films. Figure S11. Negligible hysteresis effect in the mp-GP_Cs2CO3 based PSC. Figure S12. Statistics of the efficiency distribution for 32 optimized mp-GP based PSCs. Figure S13. Thermal stability of PSCs using mp-GP and ZnO films. Table S1. Conductivity values of rGO, polyaniline, TiO2 and ZnO thin films. S-1
Figure S1. Schematic illustration of our new approach for fabricating a transparent mp-GP film consisting of rGO and aniline. Hydrazine monohydrate is used to reduce the GO sheets to increase its electrical conductivity. rGO was functionalized by polymerizing aniline on it. During the polymerization process, rGO can be further reduced and yields a highly conducting network. Polyaniline (PANI) prevents the restacking of rGO flakes and imparts positive charge on rGO. By immersing a negatively charged ITO (oxygen plasma treated) into the solution at this stage, the positively charged rGO-PANI flakes attached onto the ITO via electrostatic attraction forces. Uniform mp-GP thin films of different thicknesses could be achieved by adjusting the substrate immersion time with 1 wt% of rGO. Increasing rGO loading beyond 1 wt% in aniline solution will cause undesirable rGO aggregation. The porosity of mp-GP film is shown in the circled SEM image.
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(a)
(b)
Figure S2. (a) XRD spectra of rGO, PANI, and mp-GP showed the improved PANI crystallinity in mp-GP composite. rGO exhibited the typical peak at 26.5° that represents graphite (002) reflection. Pure PANI exhibited mainly an amorphous structure with the broad peaks at 2θ angles of 15.3°, 20°and 25.2° which are associated with the semi-crystalline PANI.1 These peaks in PANI might have arisen because of the regular repetition of the monomer unit aniline. In contrast to PANI, XRD peaks of the mp-GP were intensified and shifted to 17.2°, 21.5° and 27° indicating the formation of highly ordered and conducting crystalline structure.1 No prominent peaks shift were observed between mp-GP composites consisted of various rGO content in PANI. However, the relative intensities of all peaks increased with rGO content while FWHM decreased. (b) The intensity of (020) XRD peak measured from mp-GP composite was increasing with larger loading of rGO. The incorporation of rGO in the mp-GP composites enhanced the crystallinity of PANI leading to stronger XRD intensity from these well-organized domains. FWHM was decreasing with increase in rGO loading which showed the increment in crystallites size as calculated from the Scherrer formula (crystal size is proportional to 1/FWHM).
S-3
Figure S3. The optical bandgap (Eg) of perovskite coated on mp-GP scaffold was determined to be 1.51 eV from the extrapolation of the liner part of (αh)2 =A(h – Eg) plot which indicated that the optical absorption in the perovskite sensitizer occurred via a direct transition.
S-4
1wt% rGO
0.5wt% rGO
0.2wt% rGO
Figure S4. Sizes and morphology of perovskite grown on mp-GP with 0.2, 0.5 and 1wt% of rGO loading were similar to each other.
Figure S5. Comparison of energy level alignment at the interfaces of perovskite/OMeTAD and perovskite/PffBT4T-2OD is shown. The deeper HOMO level of PffBT4T-2OD compared to OMeTAD provides a well-aligned energy level to the valence band edge of perovskite that results in a barrier-free interface at the perovskite/PffBT4T-2OD system for hole collection.
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Figure S6. UPS spectra of Cs2CO3 coated mp-GP and mp-GP films.
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(a)
(b)
Figure S7. AFM images of perovskite grown on (a) Cs2CO3 coated mp-GP and (b) mp-GP films. Similar crystallites size and surface morphology of the perovskites indicate that Cs2CO3 will not affect perovskite formation.
Figure S8. Optical absorption property of perovskite grown on Cs2CO3 coated mp-GP and mp-GP films.
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Figure S9. Electron mobility measurement of mp-GP with 1wt % rGO using the spacecharge limited current of device.
S-8
(a) Al covered rGO rGO
1
(b)
3
U
4
2
I
Aluminum rGO, polyaniline, TiO2 or ZnO Glass
Al was used to induce a better contact between probes and rGO. With the equation of where 𝜎 is the conductivity, 𝑑 is the thickness of rGO, 𝐼12 is the current applied from 1 to 2 points, and 𝑈34 is the voltage measured between 3 and 4 points. Figure S10. (a) Top-view of sample prepared for measuring the conductivity of rGO films via four-point probes measurement was shown. (b) Conductivities of polyaniline, TiO2 and ZnO thin films were also measured under same device configuration. Measured conductivity values were summarized in Table S1. All layers were spin coated on glass and followed by aluminium (Al) evaporation. Spin coating condition of rGO (10mg/ml in DMF) and PANI (0.5M aniline and 0.12M potassium persulfate in 20 ml 1M HCl acid) was 700rpm, 30s, followed by 1200rpm, 40s. Preparation of ZnO thin film was same as those prepared in photovoltaic devices (mentioned in EXPERIMENTAL SECTION). For TiO2 film, 30 nm dense TiO2 layer was firstly prepared by spin coating (4000 rpm for 30 s) 0.15 M titanium diisopropoxide bis(acetylacetonate) from 1-butanol, followed by heating at 120 °C for 5 min. This procedure was repeated twice with 0.3 M titanium diisopropoxide bis(acetylacetonate) solution from 1-butanol, followed by heating at 150 °C for 15 min. 250 nm mesoporous TiO2 layer was deposited on dense TiO2 by spin coating (5000 rpm for 30 s) Dyesol 18NR-T paste from ethanol (1 g of paste in 3.5 g of ethanol), followed by heating at 150 °C for 15 min.
Table S1. Conductivity values of mp-GP, polyaniline, TiO2 and ZnO thin films.
Conductivity (Scm-1)
rGO
Polyaniline
TiO2
ZnO
3.1 x 10
Too low, cannot be measured
2.8 x 10-4
1.7 x 10-1
S-9
Figure S11. Negligible hysteresis effect in the mp-GP_Cs2CO3 based PSC.
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Figure S12. Statistics of the efficiency distribution for 32 optimized mp-GP based PSCs.
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Figure S13. Thermal stability of PSCs using mp-GP and ZnO. All devices were annealed under 150 °C for 30 minutes. The inset images show the real photographs of perovskite on different ETLs before and after annealing.
Reference: 1. Pouget, J. P.; Józefowicz, M. E.; Epstein, A. J.; Tang, X.; MacDiarmid, A. G. X-ray Structure of Polyaniline Macromolecules 1991, 24, 779-789.
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Thermally Stable Mesoporous Perovskite Solar Cells incorporating Low-Temperature Processed Graphene/Polymer Electron Transporting Layer Shi Wun Tong, Janardhan Balapanuru, Deyi Fu and Kian Ping Loh* *Department of Chemistry and Centre for Advanced 2D Materials, National University of Singapore, 3 Science Drive 3, Singapore 119260 *Corresponding Author: [email protected] Contents Figure S1. Preparation routes of mesoporous graphene (mp-GP) film deposited on ITO substrate. Figure S2. (a) XRD spectra of rGO, PANI and mp-GP films. (b) Under different loading of rGO, the intensity and the FWHM of (020) XRD peak inside mp-GP composite. Figure S3. The optical bandgap of perovskite coated on mp-GP scaffold. Figure S4. SEM images of perovskite grown on mp-GP scaffolds with 0.2, 0.5 and 1wt% of rGO loading. Figure S5. Comparison of energy level alignment at the interfaces of perovskite/OMeTAD and perovskite/PffBT4T-2OD. Figure S6. UPS spectra of Cs2CO3 coated mp-GP and mp-GP scaffolds. Figure S7. AFM images of perovskite grown on Cs2CO3 coated mp-GP and mp-GP scaffolds. Figure S8. Optical absorption property of perovskite grown on Cs2CO3 coated mp-GP and mp-GP scaffolds. Figure S9. Electron mobility measurement of mp-GP scaffold with 1wt % rGO using the space-charge limited current of device. Figure S10. Four-point probes measurement of rGO, polyaniline, TiO2 and ZnO thin films. Figure S11. Negligible hysteresis effect in the mp-GP_Cs2CO3 based PSC. Figure S12. Statistics of the efficiency distribution for 32 optimized mp-GP based PSCs. Figure S13. Thermal stability of PSCs using mp-GP and ZnO films. Table S1. Conductivity values of rGO, polyaniline, TiO2 and ZnO thin films. S-1
Figure S1. Schematic illustration of our new approach for fabricating a transparent mp-GP film consisting of rGO and aniline. Hydrazine monohydrate is used to reduce the GO sheets to increase its electrical conductivity. rGO was functionalized by polymerizing aniline on it. During the polymerization process, rGO can be further reduced and yields a highly conducting network. Polyaniline (PANI) prevents the restacking of rGO flakes and imparts positive charge on rGO. By immersing a negatively charged ITO (oxygen plasma treated) into the solution at this stage, the positively charged rGO-PANI flakes attached onto the ITO via electrostatic attraction forces. Uniform mp-GP thin films of different thicknesses could be achieved by adjusting the substrate immersion time with 1 wt% of rGO. Increasing rGO loading beyond 1 wt% in aniline solution will cause undesirable rGO aggregation. The porosity of mp-GP film is shown in the circled SEM image.
S-2
(a)
(b)
Figure S2. (a) XRD spectra of rGO, PANI, and mp-GP showed the improved PANI crystallinity in mp-GP composite. rGO exhibited the typical peak at 26.5° that represents graphite (002) reflection. Pure PANI exhibited mainly an amorphous structure with the broad peaks at 2θ angles of 15.3°, 20°and 25.2° which are associated with the semi-crystalline PANI.1 These peaks in PANI might have arisen because of the regular repetition of the monomer unit aniline. In contrast to PANI, XRD peaks of the mp-GP were intensified and shifted to 17.2°, 21.5° and 27° indicating the formation of highly ordered and conducting crystalline structure.1 No prominent peaks shift were observed between mp-GP composites consisted of various rGO content in PANI. However, the relative intensities of all peaks increased with rGO content while FWHM decreased. (b) The intensity of (020) XRD peak measured from mp-GP composite was increasing with larger loading of rGO. The incorporation of rGO in the mp-GP composites enhanced the crystallinity of PANI leading to stronger XRD intensity from these well-organized domains. FWHM was decreasing with increase in rGO loading which showed the increment in crystallites size as calculated from the Scherrer formula (crystal size is proportional to 1/FWHM).
S-3
Figure S3. The optical bandgap (Eg) of perovskite coated on mp-GP scaffold was determined to be 1.51 eV from the extrapolation of the liner part of (αh)2 =A(h – Eg) plot which indicated that the optical absorption in the perovskite sensitizer occurred via a direct transition.
S-4
1wt% rGO
0.5wt% rGO
0.2wt% rGO
Figure S4. Sizes and morphology of perovskite grown on mp-GP with 0.2, 0.5 and 1wt% of rGO loading were similar to each other.
Figure S5. Comparison of energy level alignment at the interfaces of perovskite/OMeTAD and perovskite/PffBT4T-2OD is shown. The deeper HOMO level of PffBT4T-2OD compared to OMeTAD provides a well-aligned energy level to the valence band edge of perovskite that results in a barrier-free interface at the perovskite/PffBT4T-2OD system for hole collection.
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Figure S6. UPS spectra of Cs2CO3 coated mp-GP and mp-GP films.
S-6
(a)
(b)
Figure S7. AFM images of perovskite grown on (a) Cs2CO3 coated mp-GP and (b) mp-GP films. Similar crystallites size and surface morphology of the perovskites indicate that Cs2CO3 will not affect perovskite formation.
Figure S8. Optical absorption property of perovskite grown on Cs2CO3 coated mp-GP and mp-GP films.
S-7
Figure S9. Electron mobility measurement of mp-GP with 1wt % rGO using the spacecharge limited current of device.
S-8
(a) Al covered rGO rGO
1
(b)
3
U
4
2
I
Aluminum rGO, polyaniline, TiO2 or ZnO Glass
Al was used to induce a better contact between probes and rGO. With the equation of where 𝜎 is the conductivity, 𝑑 is the thickness of rGO, 𝐼12 is the current applied from 1 to 2 points, and 𝑈34 is the voltage measured between 3 and 4 points. Figure S10. (a) Top-view of sample prepared for measuring the conductivity of rGO films via four-point probes measurement was shown. (b) Conductivities of polyaniline, TiO2 and ZnO thin films were also measured under same device configuration. Measured conductivity values were summarized in Table S1. All layers were spin coated on glass and followed by aluminium (Al) evaporation. Spin coating condition of rGO (10mg/ml in DMF) and PANI (0.5M aniline and 0.12M potassium persulfate in 20 ml 1M HCl acid) was 700rpm, 30s, followed by 1200rpm, 40s. Preparation of ZnO thin film was same as those prepared in photovoltaic devices (mentioned in EXPERIMENTAL SECTION). For TiO2 film, 30 nm dense TiO2 layer was firstly prepared by spin coating (4000 rpm for 30 s) 0.15 M titanium diisopropoxide bis(acetylacetonate) from 1-butanol, followed by heating at 120 °C for 5 min. This procedure was repeated twice with 0.3 M titanium diisopropoxide bis(acetylacetonate) solution from 1-butanol, followed by heating at 150 °C for 15 min. 250 nm mesoporous TiO2 layer was deposited on dense TiO2 by spin coating (5000 rpm for 30 s) Dyesol 18NR-T paste from ethanol (1 g of paste in 3.5 g of ethanol), followed by heating at 150 °C for 15 min.
Table S1. Conductivity values of mp-GP, polyaniline, TiO2 and ZnO thin films.
Conductivity (Scm-1)
rGO
Polyaniline
TiO2
ZnO
3.1 x 10
Too low, cannot be measured
2.8 x 10-4
1.7 x 10-1
S-9
Figure S11. Negligible hysteresis effect in the mp-GP_Cs2CO3 based PSC.
S-10
Figure S12. Statistics of the efficiency distribution for 32 optimized mp-GP based PSCs.
S-11
Figure S13. Thermal stability of PSCs using mp-GP and ZnO. All devices were annealed under 150 °C for 30 minutes. The inset images show the real photographs of perovskite on different ETLs before and after annealing.
Reference: 1. Pouget, J. P.; Józefowicz, M. E.; Epstein, A. J.; Tang, X.; MacDiarmid, A. G. X-ray Structure of Polyaniline Macromolecules 1991, 24, 779-789.
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