Supporting information. Supramolecular Halogen Bond Passivation of Organometal-Halide Perovskite Solar Cells

Transcription

1 Supporting information Supramolecular Halogen Bond Passivation of Organometal-Halide Perovskite Solar Cells Antonio Abate, a Michael Saliba, a Derek J. Hollman, a Samuel D. Stranks, a K. Wojciechowski, a Roberto Avolio, b Giulia Grancini, c Annamaria Petrozza, c Henry J. Snaith a * a Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom b Institute of Polymer Chemistry and Technology (ICTP), National Research Council of Italy, Via Campi Flegrei 34, Pozzuoli (NA), Italy c Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia, Via Pascoli 70/3, Milano, Italy * Corresponding authors: HJS h.snaith1@physics.ox.ac.uk 1

2 Index Figure S1. X-ray scattering patterns and light absorptance spectra of perovskite films coated upon mesoporous Al 2 O 3 scaffolds, with and without IPFB. Figure S2. Device performance variations with substrate temperature for perovskite deposition. Figure S3. Device performance variations with and without IPFB. Figure S4. Device performance parameters for record batch with IPFB treatment. Figure S5. Ultrafast transient absorption spectra of perovskite film with Spiro-OMeTAD in visible and near IR region, with and without IPFB. Figure S6. Quasi-steady-state photoinduced absorption (PIA) of perovskite film with and without Spiro- OMeTAD. Figure S7. Device performance parameters for PSSCs 1.5 µm thick mesoporous TiO 2, with and without IPFB. Figure S8. Photovoltage and photocurrent decay measurement for DSSCs, with and without IPFB. Figure S9. Photocurrent decay measurement for PSSCs, with and without IPFB. Figure S10. Photovoltage decay measurement for MSSCs, with and without IPFB. Figure S11. Device performance parameters for DSSCs, with and without IPFB. Figure S12. Device performance parameters for MSSCs, with different perfluorocarbon treatments. Figure S13. Device performance parameters for MSSCs, with iodine-free perfluorocarbon treatment. Figure S14. Stabilized steady state power output with and without IPFB treatment. Figure S15. Stabilized steady state power output for record device with IPFB treatment. Figure S16. External Quantum Efficiency (EQE) spectra of perovskite MSSCs with and without IPFB treatment. Figure S17. Solid-state 13 C and 19 F NMR spectra for IPFB as a liquid and when adsorbed onto the perovskite surface, tetra-n-butylammonium iodide and alumina. 2

3 Figure S1. X-ray scattering patterns and light absorptance spectra of perovskite films coated upon mesoporous Al 2 O 3 scaffolds, with and without IPFB. Top Figure shows powder X-ray diffraction patterns (peaks at 2θ angles of 14.1, 28.4, h h 0, h = 1,2). The films were deposited on fluorine doped tin oxide (FTO) substrate as in the complete device, with and without IPFB. Bottom Figure, light absorptance spectra of the perovskite films on glass, with and without IPFB treatment (no Spiro-OMETAD present). Experimental details are reported in the Method section. 3

4 Figure S2. Device performance variations with substrate temperature for perovskite deposition. Box chart of device parameters extracted from the current-voltage characteristic. Each point represents a single device. Before the perovskite deposition the devices were kept at room temperature (RT), heated to 50 C, 70 C, and 90 C. All the devices were treated with the IPFB after the perovskite deposition and tested at room temperature. Devices were measured as reported in Methods section. 4

5 Figure S3. Device performance variations for MSSCs with and without IPFB. Box chart of device parameters extracted from the current-voltage characteristic measured as described in the Method section. Devices were prepared with different mesoporous Al 2 O 3 thicknesses, from 100 to 1500 nm. Each point represents a single device. All devices were prepared simultaneously with and without the IPFB treatment in air as described in the Method section. For these experiments the perovskite was deposited at room temperature, not 70 C. 5

6 Figure S4. Device performance parameters for record batch with IPFB treatment. Box chart of device parameters extracted from the current-voltage characteristic. Each point represents a single device. All devices were prepared simultaneously with the IPFB treatment as described in the Method section. Devices were measured under AM1.5 simulated sun light of mw cm -2 equivalent solar irradiance using shadow masking to define the active area, as described in the Method section. 6

7 Figure S5. Ultrafast transient absorption spectra of perovskite film with Spiro-OMeTAD in visible and near IR region, with and without IPFB. Perovskite films were formed on a mesoporous Al 2 O 3 scaffold (as described in the Method section) and coated with Spiro-OMeTAD; excitation at 500 nm (14 µj/cm 2 /pulse). 7

8 Figure S6. Quasi-steady-state photoinduced absorption (PIA) of perovskite film with and without Spiro-OMeTAD. PIA spectra were collected for perovskite films with Spiro-OMeTAD as hole transporter, and poly(methyl methacrylate) (PMMA) used as an insulating organic layer to replace the hole transporter (Spiro-OMeTAD). Samples were excited using a nm laser line, chopped at 23 Hz. Contributions from photoluminescence have been removed by subtracting scans measured without the white light probe. 8

9 Figure S7. Device performance parameters for PSSCs 1.5 µm thick mesoporous TiO 2, with and without IPFB. Box chart of device parameters extracted from the current-voltage characteristic. Each point represents a single device. All devices were prepared simultaneously with and without the IPFB treatment as described in the Method section. From the data reported here is clear that for perovskite TiO 2 based devices the IPFB affects not only the FF, but also the J sc. This result can be explained considering that IPFB is a polar molecule which appears to shift the electrostatic potential at the TiO 2 surface and thus the charge injection dynamics, similarly to what reported for other polar molecules in dye-sensitized solar cells (Energy Environ. Sci. 2013, 6, ). In particular, it is well-known that 4-tert-Butylpyridine (tbp), a Lewis base, causes over 100 mev upward shift of conduction band, which reduces the charge injection efficiency within the TiO 2 (Energy Environ. Sci. 2013, 6, ). In Figure S8b (photovoltage and photocurrent decay measurement for DSSCs, with and without IPFB), we showed that IPFB, a Lewis acid, causes about 100 mev downward shift of the TiO 2 conduction band. This effect is similar to the tbp one, but in opposite direction and may justify the increase in J sc as due to a more efficient charge injection within the TiO 2. 9

10 Figure S8. Photovoltage and photocurrent decay measurement for DSSCs, with and without IPFB. Photovoltage-current decay measurements collected on dye-sensitized solar cells (DSSCs) reported in Figure S11. Data were extracted from four separate devices. a) Charge density at short circuit (ρ sc ) against short circuit photocurrent (J sc ); b) charge density at open circuit (ρ oc ) against the open circuit voltage(v oc ); c) recombination lifetimes at open circuit conditions (τ rec ) against charge density at open circuit (ρ oc ); d) transport lifetimes at short circuit conditions (τ trans ) against charge density at short circuit (ρ sc ). In PSSCs, we collected photocurrent decay lifetime at short circuit condition (τ trans ) of about s (see Figure S9 for photocurrent decay measurement for PSSCs, with and without IPFB), which are very close to the value we reported here for DSSCs (Figure S8d), where the charge transport is limited by the electron transport in the TiO 2 (Advanced Materials, Volume 25, Issue 13, pages , April 4, 2013), Therefore, in PSSCs we are slowing down the charge transport forcing the electron transport to be exclusively through the TiO 2 and thus having the perovskite working solely as TiO 2 sensitizer. To estimate the TiO 2 contribution to the relative background charge density and charge recombination with and without IPFB, we added the IPFB directly onto TiO 2 -dye surface for DSSCs (Figure S11), similarly to the procedure described in the Method section for the PSSCs. Here, in Figure S8a and S8c, we showed that no significant differences in relative background charge density and charge recombination for DSSCs with 10

11 and without IPFB. Therefore, in PSSCs any difference in charge density and charge recombination with and without IPFB can be directly assigned to the presence of the perovskite or the perovskite holetransporter heterojunction rather than TiO 2 or TiO 2 hole-transporter heterojunction. This is the same as for the Al 2 O 3 -based devices, hence we expect comparison to be fair between PSSCs and MSSCs regarding charge the background charge density and the charge recombination dynamics reported in the manuscript. The difference in charge density at open circuit (ρ oc ) against the open circuit voltage (V oc ) with and without IPFB reported here in Figure S8b can be explained considering that IPFB is a polar molecule which appears to shift the electrostatic potential at the TiO 2 surface, similarly to what reported for other polar molecules in dye-sensitized solar cells (Energy Environ. Sci. 2013, 6, ). In particular, it is wellknown that 4-tert-Butylpyridine (tbp), a Lewis base, causes over 100 mev upward shift of conduction band (Energy Environ. Sci. 2013, 6, ). IPFB, a Lewis acid, causes about 100 mev downward shift of the TiO 2 conduction band. This effect is similar to the tbp one, but in opposite direction. 11

12 Figure S9. Photocurrent decay measurement for PSSCs, with and without IPFB. Transport lifetimes (τ trans ) were extracted by the photocurrent decay probed at short circuit condition, as described in the Method section. 12

13 Figure S10. Photovoltage decay measurement for MSSCs, with and without IPFB. Recombination lifetimes (τ rec ) were extracted by the photovoltage decay probed at open circuit condition for alumina based devices (MSSCs) as described in the Method section. At the same open circuit voltage the IPFB treated devices show a longer recombination lifetime than the untreated devices, in good agreement with the recombination lifetimes reported for PSSCs in Figure 4a. 13

14 Figure S11. Device performance parameters for DSSCs, with and without IPFB. Box chart of device parameters extracted from the current-voltage characteristic. Each point represents a single device. All devices were prepared according to the procedure previously reported (Physical Chemistry Chemical Physics 15,7, ), adding IPFB as described in the Method section. 14

15 Figure S12. Device performance parameters for MSSCs, with different perfluorocarbon treatments. Box chart of device performance parameters extracted from the current-voltage characteristic. Each point represents a single device. All devices were prepared simultaneously at room temperature in inert atmosphere, with different perfluorocarbon treatments and measured in air as describe in the Method section. We used halogen bonding donor aliphatic iodoperfluorocarbon with different chain lengths: perfluoro-n-butyl iodide (PFBI), perfluoro-n-hexyl iodide (PFHI) and perfluorodecyl-n-iodide (PFDI) to establish the role of the dielectric barrier due to fluorocarbons. As known from literature (J. Mater. Chem. A, 2013, 1, ), the tendency of aliphatic iodoperfluorocarbons to phase segregate increases with the chain length. If a stronger phase segregation and thus a larger dielectric barriers at perovskite-hole transporter interface could help to further reduce hole recombination, we would expect to observe improvement in the open-circuit voltage (V oc ) and fill factor (FF) moving from perfluoro-n-butyl iodide to perfluorodecyl-n-iodide. However, the data reported here show that the device performances decrease as the chain length increases, with the shorter chain perfluorinated molecule performing closer to IPFB. Device merit parameters were extracted from the current-voltage characteristic measured as reported in the Method section. 15

16 Figure S13. Device performance parameters for MSSCs, with iodine-free perfluorocarbon treatment. Box chart of device performance parameters extracted from the current-voltage characteristic measured as reported in the Method section. Each point represents a single device. All devices were prepared simultaneously at room temperature in inert atmosphere, with iodine-free perfluorocarbon treatment. We used iodine-free perfluorocarbon (hexafluorobenzene, HFB), which cannot make halogen bond, to establish the relative role of the halogen bond and perfluoroaromatic moiety. 16

17 17

18 Figure S14. Stabilized steady state power output with and without IPFB treatment. Forward bias to short-circuit (red curve) and short-circuit to forward bias (black curve) current voltage curves measured under AM1.5 simulated sun light of MSSCs without (first figure) and with IPFB (second figure), for three independent devices prepared simultaneously as described in the Method section. The current-voltage (JV) curves were recorded as reported in Methods section. Photocurrent density as a function of time for the same cells held at 0.72 V forward bias (around the maximum power point extracted from the forward bias to short-circuit JV curve) are reported on the right-hand side. The photocurrent after 400 s under constant applied voltage (0.72 V) and illumination is reported as single point in the JV graph. The third figure shows that statistical distribution of the ratio between the current collected during the JV scan from forward bias to short-circuit (red curve) and the stabilized steady state current after 400 s, both with 0.72 V forward applied bias. 18

19 Figure S15. Stabilized steady state power output for record device with IPFB treatment. Photocurrent density (J sc ) and power conversion efficiency (PCE) as a function of time for the same cell held at 0.81 V forward bias (voltage at max power output measured from JV curve). The cell was in the dark under open-circuit prior to the start of the measurement. Over 15% PCE was recorded after 150 s under continues applied voltage (0.81 V) and illumination AM1.5 simulated sun light of 100 mw cm -2 equivalent solar irradiance using shadow masking to define the active area, as described in the Method section. 19

20 Figure S16. External Quantum Efficiency (EQE) spectra of perovskite MSSCs with and without IPFB treatment. Photovoltaic action spectra was measured (2400 Series SourceMeter, Keithley Instruments) with chopped monochromatic light incident which were biased with white light-emitting diodes (LED) at an equivalent solar irradiance of 30 mw cm -2. The monochromatic light intensity was calibrated with a UV-enhanced silicon photodiode. The JV curve was measured according to the procedure described in the Method section. In the top figure, we reported the spectral response of a cell with IPFB treatment which produced 20.3 macm -2 under 100 mwcm -2 AM1.5 illumination (inset top figure). The integration of the EQE spectrum over the 100 mwcm -2 AM1.5 solar spectrum between 400 to 850 nm gives a photocurrent of 18.8 macm -2. This is lower than that measured under the simulator, but assuming the EQE remains around 20

21 80% to 350 nm an additional 1 macm -2 of the 1.5 macm -2 discrepancy is likely to originate from the light absorbed between 350 to 400 nm. The remaining 0.5 macm -2 is 2.5% of the total value, certainly within the level of confidence of the measurement (Snaith, H.J. Energy & Environmental Science 5, , 2012). In the bottom figure, we reported the EQE spectra for four devices with and without IPFB treatment that produced similar stabilized short circuit current density of about 14 macm -2 under 100 mwcm -2 AM1.5 illumination. The spectra show no significant differences with and without the IPFB treatment. 21

22 Figure S17. Solid-state 13 C and 19 F NMR spectra for IPFB as a liquid and when adsorbed onto the perovskite surface, tetra-n-butylammonium iodide and alumina. The top 13 C and 19 F NMR spectra were collected for samples prepared as described in the manuscript replacing the perovskite with tetra-nbutylammonium iodide as halogen bond donor. This salt has been reported coordinating via halogen bond aromatic iodoperfluorocarbons (Chem. Commun., 2008, ). Both the NMR spectra showed very similar trend to what we observed with the perovskite (IPFB on perovskite). We see that the chemical shifts of iodopentafluorobenzene coordinating tetra-n-butylammonium iodide and perovskite for both 22

23 nuclei move in the same direction; although C 1 change is 1-2 ppm larger for tetra-n-butylammonium iodide, probably due to the different strength of the formed bond. Then, we performed another experiment using alumina nanoparticles dispersion to adsorbed iodopentafluorobenzene on the metal oxide surface with a preparation procedure similar to what we used for the perovskite samples described in the manuscript (IPFB on alumina). Fluorocarbons have been reported adsorbed on alumina via π or fluorine mediated interaction (Langmuir 23, , 2007). However, we did not observe significant changes in the chemicals shift comparable to IPFB on perovskite. These experiments support the conclusion reported in the manuscript that the adsorption of IPFB on the surface of perovskite crystals is driven by a halogen bond. 23