Highly Efficient Perovskite Solar Cells with ... - Semantic Scholar
Supporting information for:
Highly Efficient Perovskite Solar Cells with Tuneable Structural Color Wei Zhang1†, Miguel Anaya2†, Gabriel Lozano2, Mauricio E. Calvo2, Michael B. Johnston1, Hernán Míguez2*, Henry J. Snaith1* 1
Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK 2
Instituto de Ciencia de Materiales de Sevilla Consejo Superior de Investigaciones, Científicas-Universidad de Sevilla, Américo Vespucio 49, Sevilla, 41092, Spain †
W. Z. and M. A. contributed equally to this work.
Corresponding Authors *E-mail: [email protected]. *E-mail: [email protected] Methods Preparation of photonic crystals (PCs) One dimensional PCs were prepared using a TiO2 dispersion obtained by sol-gel techniques, a suspension of SiO2 nanoparticles and a solution of polystyrene. TiO2 dispersion was obtained by mixing titanium tetraisopropoxide in an ethanolic solution of hydrochloric acid. SiO2 colloids (Ludox TMA, Aldrich) and polystyrene (Mw 280,000 Aldrich) were diluted in methanol to 3 wt% and in toluene to 0.5 wt%, respectively. Fluorine-doped tin oxide (FTO) coated glass (TEC 7, 7Ω/sq) was used as substrate in this work. Initially, FTO was removed from regions under the anode contact by etching with a 2 M HCl solution and zinc powder. Substrate was then cleaned sequentially in 2% Hellmanex, acetone, 2-propanol and oxygen plasma. PCs were built by an alternated deposition of the three compounds over FTO glass using a spin coater (Laurell WS-400E-6NPP) in which both the acceleration ramp and the final rotation speed could be precisely determined. The first layer was deposited using 200 µL of TiO2 dispersion and then the sample was accelerated up to different final speeds with nominal value between 2000 and 3000 rpm. The total spin-coating process (ramping-up and final speed) was completed in 60 s. Then, the sample was treated at a temperature of 500 ºC during 200 s in order to densify the TiO2 film. After cooling the substrate in a metal surface at room temperature, 200 µL of SiO2 1
nanoparticles solution were deposited using final speeds with nominal value between 3000 and 8000 r.p.m for 60 s. In order to fill the voids network of this last layer, 200 µL of polystyrene solution were spin-coated at 4500 r.p.m for 60 s. This last step allows us to deposit on top a layer of TiO2 without penetration within the SiO2 nanoparticulated layer. After that, the sample is heated again at 500 ºC during 200 s, in order to remove the polystyrene and to densify the TiO2 layer.. This sequence was repeated until a total of 5 to 7 layers, depending on the cell, were deposited on top of FTO. Finally the sample is treated at 500 ºC during 30 min. Perovskite solution preparation. Methylammonium iodide (CH3NH3I) was prepared by reacting methylamine, 33 wt% in ethanol (Sigma-Aldrich), with hydroiodic acid (HI) 57 wt% in water (SigmaAldrich), at room temperature. Typical quantities were 24 mL methylamine, 10 mL hydroiodic acid and 100 mL ethanol. Upon drying at 100 oC, a white powder was formed, which was placed overnight in a vacuum oven and rinsed with ethanol before use. To generate the perovskite solution, CH3NH3I and PbCl2 (Sigma-Aldrich) were dissolved in anhydrous N,N-Dimethylformamide (DMF) at a 3:1 molar ratio with final concentrations of ~ 40 wt%. Perovskite deposition For devices, the perovskites were deposited onto PC scaffolds by spin-coating a 40 wt% solution at 2000 r.p.m in a nitrogen-filled glovebox. After spin-coating, samples were annealed at 100 °C for 2 h. The spiro-OMeTAD hole-transporting layer was then deposited from a 80 mM chlorobenzene solution containing additives of lithium bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine. Finally, 50 nm gold electrodes were thermally evaporated under vacuum of ~10-6 Torr, at a rate of ~0.1nm/s, to complete the devices. Structural, optical and photovoltaic characterization Cross-section field emission scanning electron microscopy (FESEM) images of PCs and corresponding full devices were taken by using a microscope Hitachi 5200 operating at 5kV. The spectral optical response of the PCs and full devices were obtained using a light source (Ocean Optics HL-2000) as the incident beam and an integrating sphere (Labsphere RTC-060-SF). The current density–voltage (J-V) curves were measured (2400 Series SourceMeter, Keithley Instruments) under 2
simulated AM 1.5 sunlight at 100 mWcm-2 irradiance generated by an Abet Class AAB sun 2000 simulator, with the intensity calibrated with an NREL calibrated KG5 filtered Si reference cell. The mismatch factor was calculated to be less than 1%. The solar cells were masked with a metal aperture to define the active area, typically 0.0625 cm2 (measured individually for each mask) and measured in a light-tight sample holder to minimize any edge effects and ensure that the reference cell and test cell are located in the same spot under the solar simulator during measurement. External quantum efficiency (EQE) was measured via Fourier-transform photocurrent spectroscopy using a Bruker Vertex 80v Fourier Transform Interferometer with tungsten lamp source, CaF2 beam splitter and a Stanford Research SR570 current preamplifier. Samples were calibrated to a Newport-calibrated reference silicon solar cell with a known external quantum efficiency. The solar cells were masked with a metal aperture to define the active area, typically 0.0625 cm-2. Optical modelling of the solar cell The perovskite solar cell, that integrates PCs in which dense and porous layers are alternated, is herein modeled through a layered structure, as depicted in Figure 1a. The incoming and outgoing media are considered to be the glass substrate and the air. In our model (full details are provided in Reference 1), the optical effects due to the presence of all layers comprising the photovoltaic device (see SEM cross sectional image in Figure 1b) are accounted, i.e. glass, FTO, perovskite-infiltrated PC, perovskite overlayer, spiro-OMeTAD, gold and air. This theoretical model serves to describe the optical reflectance of the PC based devices shown as solid lines in Figure 2a. As in the experiments, the calculation considers a plane wave that impinges perpendicularly to the electrode and therefore to the stacking of dielectric layers. The optical constants of the different constituents of the stack, i.e. glass, FTO, spiroOMeTAD and Au, are taken from literature.2-4 The complex refractive index of the perovskite is attained by the simultaneous fitting of the reflectance and transmittance of thin layers of the perovskite absorber deposited over a glass substrate. The effective complex dielectric permittivity of the layers infiltrated by perovskite, which comprise the PC, are approximated by the volume-weighted average of the permittivity of each component within the layer, i.e. SiO2 or TiO2 and perovskite. To obtain the reflectance of the cell, the amplitude of the electric field in the incident medium is calculated by solving the set of equations established by imposing the 3
continuity of the electric and magnetic field across each interface using a method based on the transfer matrix formalism. A linear least-squares method is employed to fit the experimental reflectance. We consider the thickness of the perovskite overlayer, the thickness of the spiro-OMeTAD layer and the thickness of the layers comprising the unit cell of the PC as fitting parameters. Figure 2a shows the comparison between the reflectance spectra measured and calculated according to the method described herein. The color hue of a PC-based cell is obtained from its reflectance spectrum. The region delimited by a dashed line in the CIE 1931 chromaticity diagram shown in Figure 2d represents the PC gamut. It encompasses the different hues that can be achieved tuning the unit cell of the PC. Using the optical model previously described, we have calculated the reflectance spectrum of cells in which the thickness of each constituent layer of the PC was varied from 10 to 150 nm. As a consequence, the lattice parameter of the unit cell ranges from 20 to 300 nm. The porosities of the high and low index materials are considered to be 4% and 50%, respectively.
Figure S1. Device performance of perovskite solar cells based on PCs comprising alternated both mesoporous nanoparticle-based TiO2 and SiO2 layers with lattice parameter of 180 nm and total multilayer thickness ca. 800 nm, for which performance is significantly poorer.
4
Figure S2. (a) Backscattered electrons field emission scanning electron microscope image of the photonic crystal (PC) scaffold infiltrated by the perovskite. Brighter areas within nanoparticle-based SiO2 layers are due to perovskite infiltration. Perovskite accumulation over TiO2 layers can be also observed. (b, c) Reflectance spectra of two PC scaffolds before (gray lines) and after the infiltration with perovskite, which lead to a (b) blue-green and (c) orange device.
Figure S3. (a) Calculated absorptance and reflectance spectra of the PC-based orange (orange lines) and blue-green (dark cyan lines) perovskite solar cells. Solid lines represent total absorptance. Dashed lines represent the fraction of the incident light absorbed by the perovskite. (b) Spectral dependence of the fraction of light absorbed by the FTO (solid lines), spiro-OMeTAD (short dashed lines), and gold (dashed lines) in PC-based orange (orange lines) and blue-green (dark cyan lines) perovskite solar cells.
5
Figure S4. CIE 1931 chromaticity space, showing the calculated color hues of the PC-based perovskite cells for the range of angles of light incidence comprised between 0º and 60º with respect to the surface normal. Two cases are evaluated, when the PC is integrated within the device (solid line) and when the light impinges directly on the photonic crystal (dashed line), a hypothetical case in which no FTO coated glass is considered. Please notice that the color change perceived from different angles is much larger in the latter case.
Figure S5. Device performance of reference perovskite solar cells realized employing ~ 370 nm thick mesoporous SiO2 as scaffold.
6
Figure S6. Digital camera pictures of the colorful devices integrating different PCs.
Figure S7. (a-d) Current-density/voltage (J-V) curves of the typical device using (a) PC and (c) mesoporous SiO2 as scaffold, measured under simulated AM 1.5 sunlight of 100 mW/cm2 irradiance, and the corresponding stabilized current density and power output of the same device using (b) PC and (d) mesoporous SiO2 as scaffold. All J-V scans were performed from forward bias to short circuit (FB-SC) and from short circuit to forward bias (SC-FB) at a scan rate of 0.15 V/s.
7
References (1) Anaya, M.; Lozano, G.; Calvo, M. E.; Zhang, W.; Johnston, M. B.; Snaith, H. J.; Miguez, H. J. Phys. Chem. Lett. 2015, 6, 48-53. (2) Wenger, S.; Schmid, M.; Rothenberger, G.; Gentsch, A.; Gratzel, M.; Schumacher, J. O. J. Phys. Chem. C 2011, 115, 10218-10229. (3) Moule, A. J.; Snaith, H. J.; Kaiser, M.; Klesper, H.; Huang, D. M.; Grätzel, M.; Meerholz, K. J. Appl. Phys. 2009, 106, 073111. (4) Palik, E. D., Handbook of optical constants of solids. Academic Press: Orlando, 1985.
8
Highly Efficient Perovskite Solar Cells with Tuneable Structural Color Wei Zhang1†, Miguel Anaya2†, Gabriel Lozano2, Mauricio E. Calvo2, Michael B. Johnston1, Hernán Míguez2*, Henry J. Snaith1* 1
Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK 2
Instituto de Ciencia de Materiales de Sevilla Consejo Superior de Investigaciones, Científicas-Universidad de Sevilla, Américo Vespucio 49, Sevilla, 41092, Spain †
W. Z. and M. A. contributed equally to this work.
Corresponding Authors *E-mail: [email protected]. *E-mail: [email protected] Methods Preparation of photonic crystals (PCs) One dimensional PCs were prepared using a TiO2 dispersion obtained by sol-gel techniques, a suspension of SiO2 nanoparticles and a solution of polystyrene. TiO2 dispersion was obtained by mixing titanium tetraisopropoxide in an ethanolic solution of hydrochloric acid. SiO2 colloids (Ludox TMA, Aldrich) and polystyrene (Mw 280,000 Aldrich) were diluted in methanol to 3 wt% and in toluene to 0.5 wt%, respectively. Fluorine-doped tin oxide (FTO) coated glass (TEC 7, 7Ω/sq) was used as substrate in this work. Initially, FTO was removed from regions under the anode contact by etching with a 2 M HCl solution and zinc powder. Substrate was then cleaned sequentially in 2% Hellmanex, acetone, 2-propanol and oxygen plasma. PCs were built by an alternated deposition of the three compounds over FTO glass using a spin coater (Laurell WS-400E-6NPP) in which both the acceleration ramp and the final rotation speed could be precisely determined. The first layer was deposited using 200 µL of TiO2 dispersion and then the sample was accelerated up to different final speeds with nominal value between 2000 and 3000 rpm. The total spin-coating process (ramping-up and final speed) was completed in 60 s. Then, the sample was treated at a temperature of 500 ºC during 200 s in order to densify the TiO2 film. After cooling the substrate in a metal surface at room temperature, 200 µL of SiO2 1
nanoparticles solution were deposited using final speeds with nominal value between 3000 and 8000 r.p.m for 60 s. In order to fill the voids network of this last layer, 200 µL of polystyrene solution were spin-coated at 4500 r.p.m for 60 s. This last step allows us to deposit on top a layer of TiO2 without penetration within the SiO2 nanoparticulated layer. After that, the sample is heated again at 500 ºC during 200 s, in order to remove the polystyrene and to densify the TiO2 layer.. This sequence was repeated until a total of 5 to 7 layers, depending on the cell, were deposited on top of FTO. Finally the sample is treated at 500 ºC during 30 min. Perovskite solution preparation. Methylammonium iodide (CH3NH3I) was prepared by reacting methylamine, 33 wt% in ethanol (Sigma-Aldrich), with hydroiodic acid (HI) 57 wt% in water (SigmaAldrich), at room temperature. Typical quantities were 24 mL methylamine, 10 mL hydroiodic acid and 100 mL ethanol. Upon drying at 100 oC, a white powder was formed, which was placed overnight in a vacuum oven and rinsed with ethanol before use. To generate the perovskite solution, CH3NH3I and PbCl2 (Sigma-Aldrich) were dissolved in anhydrous N,N-Dimethylformamide (DMF) at a 3:1 molar ratio with final concentrations of ~ 40 wt%. Perovskite deposition For devices, the perovskites were deposited onto PC scaffolds by spin-coating a 40 wt% solution at 2000 r.p.m in a nitrogen-filled glovebox. After spin-coating, samples were annealed at 100 °C for 2 h. The spiro-OMeTAD hole-transporting layer was then deposited from a 80 mM chlorobenzene solution containing additives of lithium bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine. Finally, 50 nm gold electrodes were thermally evaporated under vacuum of ~10-6 Torr, at a rate of ~0.1nm/s, to complete the devices. Structural, optical and photovoltaic characterization Cross-section field emission scanning electron microscopy (FESEM) images of PCs and corresponding full devices were taken by using a microscope Hitachi 5200 operating at 5kV. The spectral optical response of the PCs and full devices were obtained using a light source (Ocean Optics HL-2000) as the incident beam and an integrating sphere (Labsphere RTC-060-SF). The current density–voltage (J-V) curves were measured (2400 Series SourceMeter, Keithley Instruments) under 2
simulated AM 1.5 sunlight at 100 mWcm-2 irradiance generated by an Abet Class AAB sun 2000 simulator, with the intensity calibrated with an NREL calibrated KG5 filtered Si reference cell. The mismatch factor was calculated to be less than 1%. The solar cells were masked with a metal aperture to define the active area, typically 0.0625 cm2 (measured individually for each mask) and measured in a light-tight sample holder to minimize any edge effects and ensure that the reference cell and test cell are located in the same spot under the solar simulator during measurement. External quantum efficiency (EQE) was measured via Fourier-transform photocurrent spectroscopy using a Bruker Vertex 80v Fourier Transform Interferometer with tungsten lamp source, CaF2 beam splitter and a Stanford Research SR570 current preamplifier. Samples were calibrated to a Newport-calibrated reference silicon solar cell with a known external quantum efficiency. The solar cells were masked with a metal aperture to define the active area, typically 0.0625 cm-2. Optical modelling of the solar cell The perovskite solar cell, that integrates PCs in which dense and porous layers are alternated, is herein modeled through a layered structure, as depicted in Figure 1a. The incoming and outgoing media are considered to be the glass substrate and the air. In our model (full details are provided in Reference 1), the optical effects due to the presence of all layers comprising the photovoltaic device (see SEM cross sectional image in Figure 1b) are accounted, i.e. glass, FTO, perovskite-infiltrated PC, perovskite overlayer, spiro-OMeTAD, gold and air. This theoretical model serves to describe the optical reflectance of the PC based devices shown as solid lines in Figure 2a. As in the experiments, the calculation considers a plane wave that impinges perpendicularly to the electrode and therefore to the stacking of dielectric layers. The optical constants of the different constituents of the stack, i.e. glass, FTO, spiroOMeTAD and Au, are taken from literature.2-4 The complex refractive index of the perovskite is attained by the simultaneous fitting of the reflectance and transmittance of thin layers of the perovskite absorber deposited over a glass substrate. The effective complex dielectric permittivity of the layers infiltrated by perovskite, which comprise the PC, are approximated by the volume-weighted average of the permittivity of each component within the layer, i.e. SiO2 or TiO2 and perovskite. To obtain the reflectance of the cell, the amplitude of the electric field in the incident medium is calculated by solving the set of equations established by imposing the 3
continuity of the electric and magnetic field across each interface using a method based on the transfer matrix formalism. A linear least-squares method is employed to fit the experimental reflectance. We consider the thickness of the perovskite overlayer, the thickness of the spiro-OMeTAD layer and the thickness of the layers comprising the unit cell of the PC as fitting parameters. Figure 2a shows the comparison between the reflectance spectra measured and calculated according to the method described herein. The color hue of a PC-based cell is obtained from its reflectance spectrum. The region delimited by a dashed line in the CIE 1931 chromaticity diagram shown in Figure 2d represents the PC gamut. It encompasses the different hues that can be achieved tuning the unit cell of the PC. Using the optical model previously described, we have calculated the reflectance spectrum of cells in which the thickness of each constituent layer of the PC was varied from 10 to 150 nm. As a consequence, the lattice parameter of the unit cell ranges from 20 to 300 nm. The porosities of the high and low index materials are considered to be 4% and 50%, respectively.
Figure S1. Device performance of perovskite solar cells based on PCs comprising alternated both mesoporous nanoparticle-based TiO2 and SiO2 layers with lattice parameter of 180 nm and total multilayer thickness ca. 800 nm, for which performance is significantly poorer.
4
Figure S2. (a) Backscattered electrons field emission scanning electron microscope image of the photonic crystal (PC) scaffold infiltrated by the perovskite. Brighter areas within nanoparticle-based SiO2 layers are due to perovskite infiltration. Perovskite accumulation over TiO2 layers can be also observed. (b, c) Reflectance spectra of two PC scaffolds before (gray lines) and after the infiltration with perovskite, which lead to a (b) blue-green and (c) orange device.
Figure S3. (a) Calculated absorptance and reflectance spectra of the PC-based orange (orange lines) and blue-green (dark cyan lines) perovskite solar cells. Solid lines represent total absorptance. Dashed lines represent the fraction of the incident light absorbed by the perovskite. (b) Spectral dependence of the fraction of light absorbed by the FTO (solid lines), spiro-OMeTAD (short dashed lines), and gold (dashed lines) in PC-based orange (orange lines) and blue-green (dark cyan lines) perovskite solar cells.
5
Figure S4. CIE 1931 chromaticity space, showing the calculated color hues of the PC-based perovskite cells for the range of angles of light incidence comprised between 0º and 60º with respect to the surface normal. Two cases are evaluated, when the PC is integrated within the device (solid line) and when the light impinges directly on the photonic crystal (dashed line), a hypothetical case in which no FTO coated glass is considered. Please notice that the color change perceived from different angles is much larger in the latter case.
Figure S5. Device performance of reference perovskite solar cells realized employing ~ 370 nm thick mesoporous SiO2 as scaffold.
6
Figure S6. Digital camera pictures of the colorful devices integrating different PCs.
Figure S7. (a-d) Current-density/voltage (J-V) curves of the typical device using (a) PC and (c) mesoporous SiO2 as scaffold, measured under simulated AM 1.5 sunlight of 100 mW/cm2 irradiance, and the corresponding stabilized current density and power output of the same device using (b) PC and (d) mesoporous SiO2 as scaffold. All J-V scans were performed from forward bias to short circuit (FB-SC) and from short circuit to forward bias (SC-FB) at a scan rate of 0.15 V/s.
7
References (1) Anaya, M.; Lozano, G.; Calvo, M. E.; Zhang, W.; Johnston, M. B.; Snaith, H. J.; Miguez, H. J. Phys. Chem. Lett. 2015, 6, 48-53. (2) Wenger, S.; Schmid, M.; Rothenberger, G.; Gentsch, A.; Gratzel, M.; Schumacher, J. O. J. Phys. Chem. C 2011, 115, 10218-10229. (3) Moule, A. J.; Snaith, H. J.; Kaiser, M.; Klesper, H.; Huang, D. M.; Grätzel, M.; Meerholz, K. J. Appl. Phys. 2009, 106, 073111. (4) Palik, E. D., Handbook of optical constants of solids. Academic Press: Orlando, 1985.
8
