Highly Efficient Ruddlesden Popper Halide

Transcription

1 Supporting Information Highly Efficient Ruddlesden Popper Halide Perovskite PA 2 MA 4 Pb I 16 Solar Cells Peirui Cheng, 1 Zhuo Xu, 1 Jianbo Li, 1 Yucheng Liu, 1 Yuanyuan Fan, 1 Liyang Yu, 2 Detlef-M. Smilgies, 3 Christian Müller, 2 Kui Zhao 1, * and Shengzhong (Frank) Liu 1,4, * 1 Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi an 7119, China. 2 Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Göteborg, Sweden 3 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY 148, USA. 4 Dalian National Laboratory for Clean Energy, ichem, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian, 11623, P. R. China Corresponding Authors *Kui Zhao: zhaok@snnu.edu.cn. (K. Z.); *Shengzhong (Frank) Liu: szliu@dicp.ac.cn. (S. L.) 1

2 1. Experimental details and methods Crystal synthesis: The perovskite crystals of PA 2 MA 4 Pb I 16 were fistly synthesized. Lead oxide (PbO, 99%, Alladin) powder (4.464 g, 2 mmol) was dissolved in a mixture of aqueous hydriodic acid (HI, 7 wt% in H 2 O, Sinopharm Chemical Reagent Co., Ltd) solution (2. ml, 12 mmol) and aqueous hypophosphorous acid (H 3 PO 2, wt% in H 2 O, Aladdin) (3.4 ml, 31mmol). The solution was kept stirring at boiling temperature for about 2 min, followed by adding methylamine hydrochloride (MACl, 99%, Aladdin) (1.8 g, 16 mmol) to yield MAPbI 3 solution. In a separate beaker, n-ch 3 (CH 2 ) 2 NH 3 (99%, Aladdin) (321 µl, 4 mmol) was neutralized with HI ( ml, 76mmol) in an ice bath, resulting in a clear pale-yellow solution. Addition of the chilled PA solution to the MAPbI 3 solution initially produced a black precipitate, which was subsequently dissolved by heating the solution to boiling. Stirring was then discontinued, and the solution was left to cool to temperature, during which black compounds stated to crystallize. The precipitation was left to complete overnight. The crystals were isolated by suction filtration and thoroughly dried at 6 in a vacuum oven overnight. Solution for film fabrication: All solutions were prepared under inert atmosphere in a nitrogen glove box. The series of PA 2 MA 4 Pb I 16 solutions (1.2 M) were comprised of MAI (99.%, Xi an Polymer Light Technology Corp), PAI (99.%, Xi an Polymer Light Technology Corp) and PbI 2 (99.998%, Alfa Aesar) (4: 2: molar ratio) in mixed solvents of N,N-dimethylformamide (DMF, 99.9%, Aladdin) and dimethylsulfoxide (DMSO, 99.9%, Aladdin) with volume ratio of 1:, 7: 3, 1: 1, 3: 7 and : 1. The spiro-ometad solution was prepared by dissolving 9 mg spiro- OMeTAD, 22 µl lithium bis(trifluoromethanesulfonyl) imide (99%, Acros Organics, 2 mg ml -1 ) in acetonitrile (99.7+%, Alfa Aesar) and 36 µl 4-tert-butylpyridine (96%, Aldrich) in 1mL 2

3 chlorobenzene (99.8%, Aldrich). The solutions were kept at room temperature and filtered before casting. Device fabrication: The FTO-coated glass (2. cm * 2. cm) substrate was cleaned by sequential sonication in acetone, isopropanol and ethanol for 3, 3, 2 minutes, separately, and then dried under N 2 flow. The cleaned substrate was exposed to ultraviolet light for 1 minutes. The TiO 2 was prepared by chemical bath deposition with the cleaned FTO glass immersed in TiCl 4 (CP, Sinopharm Chemical Reagent Co., Ltd) aqueous solution with the volume ratio of TiCl 4 : H 2 O equal to.22: 1 at 7 for 1 hour. The TiO 2 /FTO substrates were dried under N 2 flow, and then exposed to ultraviolet and ozone for 1 minutes before hot-casting. The spin-coating was accomplished under inert atmosphere inside a nitrogen glove box. The TiO 2 /FTO substrates were preheated at ºC for minutes, followed by dropping 6 µl perovskite solution and spincoating at r.p.m. for 2 seconds without delay. The as-cast films were annealed at ºC for minutes for crystallization. The hole-transporting layer was deposited by spin-coating spiro-ometad solution at 4 r.p.m. for 3 seconds, followed by evaporation of nm gold electrode on spiro-ometad/pa 2 MA 4 Pb I 16 /TiO 2 /FTO substrate. X-ray diffraction: XRD measurements were performed on single crystals and perovskite films using a Rigaku Smart Lab X-ray diffractometer (Cu Kα radiation, λ= 1.46 Å) operating at 4 kv and 2 ma. Optical spectra: UV-Vis absorption spectra were carried out on Perkin Elmer UV-Lambda 9 UV-vis-NR spectrophotometer. PicoQuant FT-3 was used to acquire steady-state PL and timeresolved PL spectroscopy. Scanning electron microscopy: The SEM images were conducted on Hitachi SU-82 Cold Field Emission Scanning Microscopy. 3

4 Atomic force microscopy: AFM images of perovskite films were conducted on Bruke Atom Force Microscopy. Grazing incidence wide-angle X-ray scattering: GIWAXS measurements were performed at D- line at the Cornell High Energy Synchrotron Source. The wavelength of the X-ray was Å. The scattering signal was collected by Pilatus 2k detector, with a pixel size of 172 µm 172 µm placed at mm away from the sample position. The incident angle of the X-ray beam was at.3 degree. Solar cell characterization: The J-V performance of the perovskite solar cells was analyzed using Keithley 24 source under ambient condition at room temperature, and the illumination intensity was mw cm -2 (AM 1. G Oriel solar simulator). The scan rate was.3 V s -1. The delay time was ms, and the scan step was.2 V. The power output of lamp was calibrated by an NREL-traceable KG filtered silicon reference cell. The device area of.9 cm 2 was defined by a metal aperture to avoid light scattering from the metal electrode into the device during the measurement. The EQE test was conducted on the QTest Station 2ADI system (Crowntech. Inc. USA), and the light source was a 3 W xenon lamp. The monochromatic light intensity for EQE was calibrated with a reference silicon photodiode. 4

5 2. Additional data and figures Figure S1. Side views of decomposed charge densities of (a) valence band maximum (VBM), (b) conduction band maximum (CBM) (isovalue=. e Å-3), and (c) partial density of states of PA 2 MA 4 Pb I 16. The band decomposed charge densities (BDCD) of the conduction band maximum (CBM) and the valence band maximum (VBM) were analyzed to find out the composition of CBM and VBM. The CBM is mainly contributed by the Pb atoms due to their outmost p orbital; while the I atoms contribute to the VBM. The partial density of states is consistent with the BDCD analysis. The PDOS clearly shows that the main contribution to the VBM originates from the p orbitals of I atoms, while the CBM is mainly composed of p orbitals of Pb atoms. The bandgap of PA 2 MA 4 Pb I 16 is relatively larger than the bandgap of its bulk counterpart MAPbI 3. We also note that the quantum well confinement originates from the insertion of PA + cations.

6 Figure S2. The GIWAXS images of films cast from 7 : 3 DMF : DMSO, 3 : 7 DMF : DMSO, and DMSO solvents. Figure S3. (a) AFM images and (b) plan-view SEM images of the films cast from 7 : 3 DMF : DMSO and 3 : 7 DMF : DMSO solvents. 6

7 Figure S4. The cross-section SEM images of PA 2 MA 4 Pb I 16 solar cell devices fabricated from 7 : 3 DMF : DMSO and 3 : 7 DMF : DMSO solvents..6 pure DMF :3 DMF:DMSO.6 1:1 DMF:DMSO (F(R)hv) (F(R)hv) (F(R)hv) hv (ev) 3:7 DMF:DMSO hv (ev) pure DMSO hv (ev).6.2 (F(R)hv) (F(R)hv) hv (ev) hv (ev) Figure S. Tauc-plots of films fabricated from DMF, DMSO, and the mixed solvents of the two. 7

8 (a) (b) E VAC PA 2 MA 4 Pb I 16 E v -E f =1. ev Work Function(ø)= =3.92 ev Intensity (a.u.) E cutoff =17.3eV 2 1 Binding Energy (ev) Band Gap 1. ev CB=3.7 ev E F Binding Energy (ev) Binding Energy (ev) VB=.42 ev Figure S6. (a) UPS spectra in the high binding-energy region of the PA 2 MA 4 Pb I 16 film to determine the Ecutoff level and in the low-binding-energy region to determine the difference between the Fermi energy (abbreviated as E F ) and the valence band energy (E V ). (b) Energy band diagram of PA 2 MA 4 Pb I 16 film calculated from the Tauc plot (Figure S) and UPS results. The valence band is determined to be -.42 ev, which is unexpected to stay closed to its 3D counterpart (Figure S6). The band gap is ca ev. We attribute the low value of valence band to the formation of higher <n> phases which can be observed from GIWAXS images (Figure 2d) and undesired air contamination during the sample shipment. 8

9 1 pure DMF 1 7:3 DMF:DMSO 1 1:1 DMF:DMSO Current (A) 1E-4 1E-6 Current (A) 1E-4 1E-6 Current (A) 1E-4 1E-6 V TFL Voltage (V) Voltage (V) V TFL V TFL Voltage (V) 1 3:7 DMF:DMSO 1 pure DMSO.1.1 Current (A) 1E-4 1E-6 Current (A) 1E-4 1E-6 V TFL Voltage (V) V TFL 1E Voltage (V) Figure S7. Dark current-voltage measurements of the electron-only devices for the PA 2 MA 4 Pb I 16 perovskite displaying V TFL kink point behavior. 9

10 Current density (ma cm -2 ) 1 pure DMF J sc =11.46 ma cm -2 PCE=.96% Time (s) PCE (%) Current density (ma cm -2 ) DMF:DMSO=7:3 J sc =17.72 ma cm -2 PCE=9.7% Time (s) PCE (%) Current density (ma cm -2 ) DMF:DMSO=1:1 J sc =19.3 ma cm -2 PCE=.6% Time (s) PCE (%) Current density (ma cm -2 ) DMF:DMSO=3:7 J sc =17.2 ma cm -2 PCE=9.46% Time (s) PCE (%) Current density (ma cm -2 ) pure DMSO J sc =1.2 ma cm -2 PCE=8.37% Time (s) PCE (%) Figure S8. The stable output photocurrent density and PCE of these cells obtained under the standard 1 sun illumination. 1. Normalized PCE Initial After h DMF 7:3 1:1 3:7 DMSO Figure S9. PCE degradation of the cells after hours exposure to air (in the dark, relative humidity ~6% RH, 2 ºC) without encapsulation.

11 Table S1. Photovoltaic performances obtained from 3 cells for each film fabricated from different solvents. pure DMF 7:3 DMF:DMSO 1:1 DMF:DMSO 3:7 DMF:DMSO pure DMSO J sc (ma cm -2 ) 11.± ± ± ±.3 1.2±.48 V oc (V) 1.13± ± ± ±.1 1.9±.1 FF (%) 48.2± ± ± ± ±.66 PCE (%).62± ±.26.± ± ±.31 R s (ohm) 47.38± ± ± ± ±.3 R sh (ohm) 92.4± ± ± ± ±12 11