Severe Morphological Deformation of Spiro- Temperature

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1 Supplementary Information Severe Morphological Deformation of Spiro- OMeTAD in (CH 3 NH 3 )PbI 3 Solar Cells at High Temperature Ajay Kumar Jena, Masashi Ikegami, Tsutomu Miyasaka* Toin University of Yokohama, 1614 Kurogane-cho, Aoba, Yokohama, Kanagawa Experimental 2.1 Device fabrication Planar heterojunction perovskite (CH 3 NH 3 PbI 3 ) solar cells with TiO 2 compact layer as ETL and Spiro-OMeTAD as HTM were fabricated by solution method. First, FTO substrates were cleaned with soap solution, distilled water, acetone and again distilled water. A TiO 2 compact layer of 50 nm thickness was coated by spin-coating (3000 rpm x 30s) a diluted solution of titanium diisopropoxide bis (acetylacetonate) (75 wt%, Aldrich) in ethanol (100 µl Ti (acac) + 1 ml EtOH) for two times on the FTO. Then, the precursor coated FTO substrates were dried at 120 o C for 10 min, sintered at 500 o C for 1 h in a muffle furnace. These substrates were then given UV- Ozone treatment for 10 mins before the perovskite precursor solution (1M PbI 2 and 1 M MAI in DMF and DMSO mixed solvent) was coated on it. A mix solution of 1 M PbI 2 (TCI, Japan) and 1 M MAI (TCI, Japan) was prepared by mixing them in a mixed solvent of DMF and DMF (1V DMSO: 3 V DMF). The perovskite film was made by spin-coating the precursor solution at 6000

2 rpm for 25 s with dripping 1 ml of chlorobenzene just 5 s before the spin-coating stopped. The precursor coated substrates were then annealed at 100 o C on hot plate for 1 h to crystallize MAPbI 3. As measured from the cross-sectional SEM image, the thickness of the perovskite film was nm. After annealing and cooling the perovskite films to room temperature, a 12 wt% solution of 2,2',7,7'-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro- OMeTAD, from Merck) including lithium bis(trifluoromethylsyfonyl) imide salt (Li-TFSI) and tert-butylpyridine (t-bp) as dopant and additive respectively in chlorobenzene was coated at a spinning speed of 4000 rpm for 30s. The spiro-ometad layer was aged in dry and dark overnight. Au contact was thermally evaporated on to the spiro-ometad. In order to cause degradation to the devices, they were heated at 60 o C, 80 o C, 100 o C, and 120 o C for 1 h on hot plate. The performance of the cells before and after degradation was measured. 2.2 Device characterization Photovoltaic characterization of the devices was done by measuring current on voltage scan in forward (-0.1 V to 1.2 V) and backward (1.2 V to 0 V) directions both under light (100 mw cm - 2, AM1.5, 1 sun intensity) provided by a solar simulator (Peccell Technologies PEC-L01) and dark. A Keithley source meter (Model 2400) was used for all electrical measurements. The voltage scan speed used to obtain photocurrent density-voltage (J-V) curves was kept at 200 mv/s. The active area of the device was 0.09 ma/cm 2. X-ray diffraction pattern of perovskite was checked with a Bruker Model D8 Discover XRD machine before and after heat-treatment. SEM microscopy (SU8000, HITACHI) was used to check the film morphology and thickness of the layers in the device. All the measurements were taken on non-encapsulated cells in ambient atmosphere (30-40% humidity) at room temperature.

3 (a) (b) (c) (d) Figure S1. Backward scan (a) PCE, (b) J sc, (c) V oc, and (d) FF of planar MAPbI 3 perovskite solar cells before and after heating at different temperatures (60, 80, 100 and 120 o C for 1 h).

4 Figure S2 XRD patterns of planar MAPbI 3 devices taken before and after heating them at 60, 80, 100 and 120 o C for 1 hour. Figure S3 Cross-sectional SEM micrographs of the planar MAPbI 3 perovskite solar cells heated at (a) 0 and (b) 60 o C for 1 hour.

5 Figure S4 Cross-sectional SEM micrographs of FTO/spiro-OMeTAD/Au devices (a) before and (b, c) after heated at 100 o C for 1 hour. Images taken at sites where Au (a and b) covered and (c) did not cover the HTM. Figure S5 Cross-sectional SEM micrographs of FTO/spiro-OMeTAD/Au devices that were not (a) and were (b) subjected to electric field (I-V measurement) before heating at 100 o C for 1 h. Figure S6 Cross-sectional SEM micrographs of FTO/spiro-OMeTAD/Au after heating at 100 o C for 1 h. (a) spiro-ometad contained only TBP (no LiTFSI) and (b) spiro-ometad contained only LiTFSI (no TBP).

6 Figure S7 Cross-sectional SEM micrographs of FTO/Au/spiro-OMeTAD devices heated at (a) 80 o C, (b) 100 o C, and (c) 120 o C for 1 h. Figure S8 I-V curves of FTO/spiro-OMeTAD/Au devices not heated and heated at different temperatures.