Coating Evaporated MAPI Thin Films with Organic Molecules: Improved Stability at High Temperature and Implementation in High-Efficiency Solar Cells.

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1 Supporting Information for: Coating Evaporated MAPI Thin Films with Organic Molecules: Improved Stability at High Temperature and Implementation in High-Efficiency Solar Cells. Francisco Palazon, * Daniel Pérez-del-Rey, Sergio Marras, Mirko Prato, Michele Sessolo, Henk J. Bolink, and Liberato Manna. Nanochemistry Department, and Materials Characterization Facility, Istituto Italiano di Tecnologia, Via Morego 30, Genova, Italy Instituto de Ciencia Molecular, ICMol, Universidad de Valencia, C/Catedrático J. Beltrán 2, Paterna, Spain EXPERIMENTAL DETAILS Materials 2-propanol (IPA, anhydrous, 99.5%), tridodecyl methyl ammonium iodide (TDMAI, 97%), and toluene (TOL, 99.7%) were purchased from Sigma Aldrich. Trioctyl phosphine oxide (TOPO, 99%) was purchased from Strem Chemicals. Chemicals are used without further purifications. Photolithographically patterned ITO coated glass substrates were purchased from Naranjo Substrates. 2,2 -(Perfluoronaphthalene-2,6-diylidene) dimalononitrile (F6-TCNNQ), N4,N4,N4,N4 -tetra([1,1 - biphenyl]-4-yl)-[1,1 :4,1 - terphenyl]-4,4 -diamine (TaTm) and N1,N4-bis(tri-p-tolylphosphoranylidene)benzene-1,4- diamine (PhIm) were provided from Novaled GmbH. TiO 2 nanoparticle suspensions were prepared in IMEC and deposited through a low temperature process compatible with ITO substrates. Non-aqueous sol-gel route is used, 1 in which the oxygen required for the nanoparticle formation is provided by benzyl alcohol. In detail, 2 ml anhydrous ethanol is mixed with 0.5 ml titanium (IV) chloride (TiCl 4 from Sigma Aldrich) inside a nitrogen field glove box. After stirring for 10 minutes at room temperature, 10 ml benzyl alcohol (Sigma Aldrich) is added to the mixture leading to a light yellow and clear solution. This solution is stirred for at least 18 hours at 80 ºC leading to color-less hazy suspension. The haziness of the suspension is caused by creation of white titanium oxide nanoparticles. In order to separate them, 1 ml of the resulting milky suspension was precipitated in 10 ml of diethyl ether (from Sigma Aldrich) and centrifuged at 5000 rpm for two minutes to isolate the nanoparticles from the solvent and the unreacted precursor. After centrifuge, the solvent was drained out and solid white nanoparticles were dispersed into 3 ml pure ethanol leading to milky (white and hazy) solution. In order to stabilize this final dispersion, 45 µl Diisopropoxytitaan-bis-(acetylacetonaat) (TiAcac purchased from Sigma Aldrich) is added to the solution. After less than one hour, a light green and clear solution is created19. This is the final product containing of TiO 2 nanoparticles in pure ethanol. After spin coating of the TiO 2 dispersion, the substrates are annealed at 100 ºC for 15 minutes in air. Fullerene (C60) was purchased from sigma Aldrich. PbI 2 was purchased from Tokyo Chemical Industry CO (TCI), and CH 3 NH 3 I (MAI) from Lumtec. Vacuum deposition of MAPI on glass for XRD analyses MAPI thin films were prepared by dual source vacuum deposition on glass substrates obtained by co-deposition of the two precursors PbI 2 and MAI. The calibration of the deposition rate for the CH 3 NH 3 I was found to be difficult due to nonuniform layers and the soft nature of the material which impeded accurate thickness measurements. Hence, the source 1

2 temperature of the CH 3 NH 3 I was kept constant at 70 ºC and the CH 3 NH 3 I:PbI 2 ratio was controlled off line using grazing incident x-ray diffraction by adjusting the PbI 2 deposition temperature. The optimum deposition temperatures were found to be 250 ºC for the PbI 2 and 70 ºC for the CH 3 NH 3 I leading to a final thickness of 500 nm. Film coating with organic molecules MAPI films were coated either with TDMAI or with TOPO. For TDMAI coating, a 25 mm solution in dry IPA was prepared in a nitrogen-filled glovebox. MAPI films were fully immersed in this solution for 30 seconds, followed by 30 second rinse in fresh IPA, and mild annealing at 60 ºC for 5 min to dry. This procedure was adapted from Yang et al. 2 For TOPO treatment a solution at 25 mm in toluene was prepared. Then, 50 ul of TOPO solution was spin-coated on top of 1x1 cm 2 MAPI films at 2000 rpm in air. Eventually, films were rinsed by spin-coating 50ul of fresh toluene. This protocol was adapted from dequilettes et al. 3 XRD characterization High Temperature X-ray diffraction analysis (HTXRD) at 150 C was performed using a Rigaku Smartlab system equipped with a 9 kw CuKα rotating anode (operating at 40kV and 150mA) and an Anton Paar DHS 900 domed hot stage; the stage is left open in air. Samples are continuously analyzed in the range 2θ = ; each scan lasting 30 min. XPS characterization XPS characterization was performed using a Kratos Axis Ultra DLD spectrometer with a monochromatic Al Kα source (photon energy = ev) operated at 15 kv with an emission current of 20 ma. For TDMAI characterization, wide scans were acquired at an analyzer pass energy of 160 ev and steps of 1 ev. For TOPO characterization, high resolution narrow scans were performed at a pass energy of 10 ev and steps of 0.1 ev. The photoelectrons were detected at a takeoff angle Φ =0 with respect to the surface normal. The pressure in the analysis chamber was maintained below Torr for data acquisition. The data were converted to VAMAS format and processed using CasaXPS software. The binding energy scale was referenced to the C 1s peak at ev. Solar cell fabrication ITO-coated glass substrates were subsequently cleaned with soap, water and isopropanol in an ultrasonic bath, followed by UV-ozone treatment. The TiO 2 dispersion was deposited in air by spin-coating at 3000 rpm for 30 s and annealed at 100 ºC for 30 min, leading to a nm thick compact layer. Then, they were transferred to a vacuum chamber integrated into a nitrogen-filled glovebox (H 2 O and O 2 < 0.1 ppm) and evacuated to a pressure of 10-6 mbar. The vacuum chamber is equipped with six temperature controlled evaporation sources (Creaphys) fitted with ceramic crucibles. The sources were directed upwards with an angle of approximately 90º with respect to the bottom of the evaporator. The substrate holder to evaporation sources distance is approximately 20 cm. Three quartz crystal microbalance (QCM) sensors are used, two monitoring the deposition rate of each evaporation source and a third one close to the substrate holder monitoring the total deposition rate. For thickness calibration, we first individually sublimed the charge transport materials and the HTM dopant (TaTm, F6-TCNNQ and C60). A calibration factor was obtained by comparing the thickness inferred from the QCM sensors with that measured with a mechanical profilometer (Ambios XP1). Then these materials were co-sublimed at temperatures ranging from ºC for the dopants to 250 ºC for the pure charge transport molecules, and the evaporation rate was controlled by separate QCM sensors and adjusted to obtain the desired doping concentration. In general, the deposition rate for TaTm was kept constant at 0.8 Å s-1 while varying the deposition rate of the dopant during co-deposition. Pure TaTm and C60 layers were deposited at a rate of 0.5 Å s-1. For the n-i-p configuration, after deposition of the TiO 2 layer it is annealed at 100 ºC for 15 minutes in air. Then, 10 nm thick C60 is vacuum-deposited. Once completed this deposition, the chamber was vented with dry N 2 to replace the C60 crucible with those containing the starting materials for the perovskite deposition, PbI 2 and CH 3 NH 3 I. The vacuum chamber was evacuated again to a pressure of 10-6 mbar, and the perovskite films were then obtained by co-deposition of the two precursors. After deposition of a 500 nm thick perovskite film, the chamber was vented and the crucibles replaced with one containing TaTm, and evacuated again to a pressure of 10-6 mbar. The devices were completed depositing a film of pure TaTm with a thickness of 10 nm. Finally, the substrates were transferred to a second vacuum chamber where 10 nm of MoO 3 where evaporated on top of the TaTm and afterwards the metal top contact (Au, 100 nm thick) was deposited. Solar cell characterization. The external quantum efficiency (EQE) was estimated using the cell response at different wavelength (measured with a white light halogen lamp in combination with band-pass filters), where the solar spectrum mismatch is corrected using a calibrated Silicon reference cell (MiniSun simulator by ECN, the Netherlands). The current density-voltage (J-V) characteristics were 2

3 obtained using a Keithley 2400 source measure unit and under white light illumination, and the short circuit current density was corrected taking into account the device EQE. The electrical characterization was validated using a solar simulator by Abet Technologies (model with an AM1.5G xenon lamp as the light source). Before each measurement, the exact light intensity was determined using a calibrated Si reference diode equipped with an infrared cut-off filter (KG-3, Schott). The J-V curves were recorded between -0.2 and 1.2 V with 0.01V steps, integrating the signal for 20 ms after a 10 ms delay. This corresponds to a speed of about 0.3 V s -1. The layout used to test the solar cells has four equal areas ( cm 2, defined as the overlap between the ITO and the top metal contact) and measured through a shadow masks with 0.01 cm 2 aperture. Figure S 1. XPS P2p signal for pristine MAPI and films coated with 25mM and 50mM solutions of TOPO. 3

4 Figure S 2. XRD characterization of pristine (a) and TDMAI-functionalized (b) MAPI films after several weeks at room temperature. Insets show photographs of corresponding samples. 4

5 Figure S 3. I 3d and Pb 4f spectra of pristine and TOPO-coated samples after background subtraction. Open circles represent raw data points and lines represent appropriate fit with Voigt functions. The thickness of the TOPO layer is derived from the peak area ratios between pristine and TOPO-coated films (see main text for details). 5

6 Figure S 4. J-V curves of pristine MAPI and MAPI with spin-coated layers of TOPO from 25 mm and 50 mm solutions. 6

7 Figure S 5. Photovoltaic performances of three different devices prepared with a layer of TOPO. REFERENCES (1) Niederberger, M. Nonaqueous Sol Gel Routes to Metal Oxide Nanoparticles. Acc. Chem. Res. 2007, 40 (9),

8 (2) Yang, S.; Wang, Y.; Liu, P.; Cheng, Y.-B.; Zhao, H. J.; Yang, H. G. Functionalization of Perovskite Thin Films with Moisture-Tolerant Molecules. Nat. Energy 2016, 1 (2), (3) dequilettes, D. W.; Koch, S.; Burke, S.; Paranji, R. K.; Shropshire, A. J.; Ziffer, M. E.; Ginger, D. S. Photoluminescence Lifetimes Exceeding 8 Μs and Quantum Yields Exceeding 30% in Hybrid Perovskite Thin Films by Ligand Passivation. ACS Energy Lett. 2016, 1 (2),