Electronic Supplementary Information. Benjia Dou,, Vanessa L. Pool, Michael F. Toney *,, Maikel F.A.M. van Hest *,

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1 Electronic Supplementary Information Radiative Thermal Annealing/in Situ X-ray Diffraction Study of Methylammonium Lead Triiodide: Effect of Antisolvent, Humidity, Annealing Temperature Profile, and Film Substrates Benjia Dou,, Vanessa L. Pool, Michael F. Toney *,, Maikel F.A.M. van Hest *, National Renewable Energy Laboratory, Golden, CO 80401, United States Department of Electrical, Computer, and Energy Engineering, University of Colorado Boulder, Boulder, CO 80309, United States Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, United States Corresponding Authors: PbI 2 (001) (110) (112) (211) (202) (220) (110) θ ( ) (220) 10 min on hotplate 3 min with RTA 3 min on hotplate θ ( ) θ ( ) Figure S1. XRD patterns of MAPbI 3 fabricated with annealing profiles as 3 min on hotplate (yellow), 3 min with RTA (green) and 10 min on hotplate (red). Upper right and lower right are respective the peak for MAPbI 3 (110) and MAPbI 3 (220)

2 Figure S2. SEM image of MAPbI3 film fabricated a. without antisolvent and b. with antisolvent. Table S1 Device parameters corresponding to the J-V curves in Figure 2a Voc (V) Jsc (ma cm-2) FF PCE (%) RTA (3 min) Hotplate (3 min) Hotplate (10 min) With Antisolvent No Antisolvent Table S2. Device parameters shown in Figure 4a Scan Direction Voc Jsc (V) (ma/cm2) FF PCE (%)

3 c ~140 s Q (A -1 ) ~1227 s Q (A -1 ) Figure S3. Intensity Ratio of XRD peaks for MAPbI 3 (100), MAPbI 3 (110) and MAPbI 3 (111). a. blue line represents the temperature profile. I(100)/ I(110) ratio plotted as the red line, while the I(100)/ I(111) shown as the purple line. b. I(111)/ I(110) ratio shown as green line. c. 2D XRD images of annealing at ~140s and ~1227 s. After the temperature has reached 100 C, the peak intensity ratios are nearly constant in time and the images are nearly uniform arcs showing that there is little texture in the films. 3

4 Figure S4. Effect of antisolvent on light soaking. a. J-V characteristics of a device with the active layer fabricated without antisolvent, reversely scanned. b. J-V characteristics of a device with the active layer fabricated with antisolvent, reversely scanned. Table S3 Device performance corresponding to Figure S2 Light Voc Jsc FF 2 Soaking (V) (ma/cm ) Time (s) No Antisolvent With Antisolvent PCE (%)

5 Figure S5. Statistics of device performance, from reversely scanned J-V curves, with active layer annealed in N2 and air. Sample number: 24 samples in each case. Table S4. Device performance corresponding to the J-V characteristics of Figure 6a. Air N2 Voc (V) Jsc (ma/cm2) FF PCE (%)

6 Figure S6. Device J-V characteristics (reversely scanned) for different annealing steps: 65 C for 1 min and 100 C for 2 min (note as A, red line), 100 C for 3 min (note as B, green line), 65 C for 3min (note as C, yellow line), and 65 C for 1 min and 100 C for 3 min (note as D, purple line). Table S5. Device info corresponding to Figure S5 Voc (V) Jsc (ma/cm 2 ) FF PCE (%) A B C D

7 Figure S7. Device performance statistics (average values and standard deviations are presented with black lines, and the colored dots show actual data points) with different annealing steps: 65 C for 1 min and 100 C for 2 min (note as A, red dots), 100 C for 3 min (note as B, blue dots), 65 C for 3min (note as C, yellow dots), and 65 C for 1 min and 100 C for 3 min (note as D, purple dots). There are 20 devices in each case. 7

8 Effect of substrates on growing high quality MAPbI 3 film. Figure S8. in situ XRD on different substrates a. temperature profile; b. MAPbI 3 (100) peak tracking; c. MAPbI 3 (110) peak tracking; d. PbI 2 peak tracking. Surface plays a key role in determining the growth of perovskite films. Materials such as planar TiO 2, mesoscopic TiO 2 and Al 2 O 3 were developed as electron transport layers for perovskite solar cell 1 4. We compare the MAPbI 3 film growth on glass, planar TiO 2 and mesoscopic TiO2 and key peaks are tracked and shown in Figure S8, with Figure S8a as the two step RTA temperature profiles. As shown in FigureS8b, strong MAPbI 3 (100) is detected, prior to annealing, with the film deposited on meso-tio 2 and compact-tio 2. However, MAPbI 3 is not initially observed for films deposited on glass, as seen by the lack of MAPbI 3 (100) and (110) peaks shown in Figure S8c and S8b. This effect could be due to the surface wetness of the glass substrates, or TiO 2 may provide templating that the glass does not. Despite MAPbI 3 forming later on the glass, its decomposition into PbI 2 occurs (Figure S8d) at about the same time as MAPbI 3 decomposes on compact and mesoscopic TiO 2. As there is no difference is observed in the crystallization process of MAPbI 3 on the compact TiO 2 vs. mesoscopic TiO 2, we assume any difference observed in the device performances between devices built on compact TiO 2 and mesoscopic TiO 2 is due to the variations in nanoscopic morphology and homogeneity of the MAPbI 3 layer induced by different types of TiO 2. In the early stages of perovskite solar cell research, researchers 4,5 found 8

9 mesoscopic structured devices perform better than the planar devices. It is believed mesoscopic structure performs as a scaffold and helps in extracting charges by increasing the contact area between the perovskite and electron transport layer. Device performance of mesoscopic and planar TiO 2 is presented in Figure S9 and Table S6. We find that the mesostructured cells are not as efficient as the planar devices, in contrast to comparative studies 6,7 using other fabrication processes. We attribute this different to the improved film quality with the antisolvent deposition method. When high quality perovskite films (highly crystallized, pin-hole free films with good coverage) are hard to fabricate, mesostructured devices perform better than the planar devices because the mesostructured devices are a better way to contact the active layer to the ETL. However, after much optimization, particularly using solvent engineering to deposit uniform coverage films, mesostructured films are not required to make high efficiency devices. This highlights the complexity of making high quality perovskite films and the need to take great care when adopting new optimization routes. Figure S9. Effect of MAPbI3 deposition surface, planar structuare and mesoscopic structure, on device performance. a. J-V characteristics. b. Statistics, including medium value and standard deviation value, of photovoltaic performance for 57 planar devices and 24 mesoscopic devices. 9

10 Table S6. Device performance corresponding to the J-V characteristics of Figure S9. Compact TiO2 Meso TiO2 Voc(V) Jsc (ma/cm 2 ) FF PCE(%) Reference (1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131 (17), (2) Im, J.-H.; Lee, C.-R.; Lee, J.-W.; Park, S.-W.; Park, N.-G. 6.5% Efficient Perovskite Quantum-Dot-Sensitized Solar Cell. Nanoscale 2011, 3, (3) Kim, H.-S.; Lee, C.-R.; Im, J.-H.; Lee, K.-B.; Moehl, T.; Marchioro, A.; Moon, S.-J.; Humphry-Baker, R.; Yum, J.-H.; Moser, J. E.; Grätzel, M.; Park, N.-G. Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, 591. (4) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science 2012, 338, (5) Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.; Seok, S. Il. Chemical Management for Colorful, Efficient, and Stable Inorganic-Organic Hybrid Nanostructured Solar Cells. Nano Lett. 2013, 13, (6) Leijtens, T.; Lauber, B.; Eperon, G. E.; Stranks, S. D.; Snaith, H. J. The Importance of Perovskite Pore Filling in Organometal Mixed Halide Sensitized TiO2-Based Solar Cells. J. Phys. Chem. Lett. 2014, 5, (7) Listorti, A.; Juarez-Pérez, E. J.; Frontera, C.; Roiati, V.; Garcia-Andrade, L.; Colella, S.; Rizzo, A.; Ortiz, P.; Mora-Sero, I. Effect of Mesostructured Layer upon Crystalline Properties and Device Performance on Perovskite Solar Cells. J. Phys. Chem. Lett