Hybrid Perovskite/Perovskite Heterojunction Solar Cells Supporting Information Yinghong Hu 1, Johannes Schlipf 2, Michael Wussler 3, Michiel L. Petrus 1, Wolfram Jaegermann 3, Thomas Bein 1, Peter Müller-Buschbaum 2 and Pablo Docampo 1, * 1 Department of Chemistry and Center for NanoScience (CeNS), LMU Munich, Butenandtstr. 5-13, 81377 München, Germany. 2 Physik-Department, Lehrstuhl für Funktionelle Materialien, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany. 3 Department of Materials Science, Surface Science Division, Darmstadt University of Technology, Jovanka-Bontschits-Str. 2, 64287 Darmstadt, Germany. CORRESPONDING AUTHOR *P. D.: Tel: +49 (0)89 2180-77585. Fax: +49 (0)89 2180-77622. E-mail: pablo.docampo@cup.lmu.de 1
Estimation of 2θ positions of (00l) reflections for the series of layered hybrid perovskite (PEA) 2 (MA) m-1 (Pb m I 3m+1 ) The previously reported layered perovskite compounds (PEA) 2 (MA) m-1 (Pb m I 3m+1 ) with m = 1, 2, 3 exhibit (00l) reflections, where the position of the peaks shifts to lower angles with increasing m (m = number of [PbI 6 ] octahedra sheets). The interplanar distance for the (002) crystallographic planes in the layered perovskite (LPK) structures is increased by approximately 6.1 Å for each additional octahedra layer, which coincides with the distance of two axial iodine atoms along the c-axis. 1 Following this trend and by employing the Bragg equation, 2d sin θ = n λ with d as the interplanar distance, θ as the diffraction angle, n as the order of diffraction and λ as the wavelength of the X-rays, we estimated the 2θ positions of (00l) peaks for the layered perovskite series (PEA) 2 (MA) m-1 (Pb m I 3m+1 ) with m = 4, 5, 6, 7, 8 in order to identify the lowangle reflections in the experimental XRD pattern of the treated MAPI film. Table S1. Estimated 2θ positions of (00l) reflections for the series of layered perovskites (PEA) 2 (MA) m-1 (Pb m I 3m+1 ) with m as the thickness of [PbI 6 ] octahedra layer, utilizing Cu-K α1 radiation, λ = 1.5406 Å. d 002 [Å] 2θ [ ] 2θ [ ] 2θ [ ] Diffraction peaks (002) (004) (006) Experimental 2.16 4.37 6.53 m = 4 34.7 2.54 5.09 7.63 m = 5 40.8 2.16 4.32 6.48 Estimated m = 6 46.9 1.88 3.77 5.65 m = 7 53.0 1.67 3.33 5.00 m = 8 59.1 1.49 2.99 4.48 2
Figure S1. XRD patterns of a) MAPI/PEAMAPI and b) MAPI/BAMAPI bilayer films fabricated with different concentrations of the casting solution. The diffraction peaks of PEAMAPI and BAMAPI are marked with asterisks, respectively. Estimation of the crystallite size of the layered perovskite phase The crystallite size of the layered perovskite BAMAPI or PEAMAPI formed on top of a MAPI film can be estimated by analyzing the peak breadth of the corresponding X-ray diffraction peaks according the Scherrer equation: 2 D = K B cos where D is the average crystallite size, K being the Scherrer shape factor, the wavelength of the used X-ray, B the full-width-half-maximum (FWHM) value of the peak in radians and the Bragg angle of the (hkl) reflection. We fit the most intense (00l) reflection of PEAMAPI with a Gaussian function to extract the FWHM of the peak. Since the (002) peak of BAMAPI is a superposition of two phases with the [PbI 6 ] octahedra layer thickness being m = 3 and m = 4, two Gaussians were fitted and a crystal size value for each phase was estimated. The instrument broadening of the peak was taken into account by fitting a Gaussian function to the (001) 3
reflection of a highly crystalline methylammonium lead bromide sample. The measured peak broadening was considered as a convolution of two Gaussian functions correlating to the instrument contribution and the layered perovskite sample, respectively. The corrected FWHM B sample can be calculated as following: 3 B sample = B total 2 B instrument 2 where B instrument was found to be 0.067. A commonly used shape factor of K = 0.9 was employed and the determined crystallite sizes for different concentrations of the casting solution is summarized in Table S2. Table S2. Estimated crystallite size of the layered perovskite (BA) 2 (MA) m-1 (Pb m I 3m+1 ) and (PEA) 2 (MA) m-1 (Pb m I 3m+1 ) fabricated with different concentrations of the respective casting solution. Layered Perovskite BAMAPI PEAMAPI Casting solution [PbI 6 ] layer thickness Reflection (hkl) B total [ ] 2 [ ] D [nm] 10 mm BAI:MAI m = 4 (002) 0.498 2.69 16 m = 3 (002) 0.873 3.13 9 20 mm BAI:MAI m = 4 (002) 0.683 3.13 12 m = 3 (002) 0.241 3.36 34 40 mm BAI:MAI m = 4 (002) 0.427 2.87 19 m = 3 (002) 0.178 3.39 48 10 mm PEAI:MAI m = 5 (006) 0.361 6.50 22 20 mm PEAI:MAI m = 5 (006) 0.277 6.50 29 40 mm PEAI:MAI m = 5 (006) 0.188 6.52 45 4
Details on the calculation of the PEAMAPI layer thickness via GIWAXS analysis: The azimuthal integration was performed around q = 1 Å -1 and around q = 2.2 Å -1 which correspond to the Debye-Scherrer rings arising from the (002)/(110) and (213)/(114)/(310)/(222) lattice plane reflections of the MAPI crystals. For simplicity they are denoted as (002) and (222), respectively (c.f. Figure 2c). In order to quantify the amount of oriented crystals for the (002) peak, the data were fit with a Gaussian function. The 2σ range of the Gaussian was defined as the oriented part as it accounts for 95% of the area underneath the peak. The 2σ range is marked in Figure 2c by dashed lines which divide the graph into three areas. The intensities of these individual areas were integrated and normalized by the total intensity, thus determining the ratio of randomly and preferentially oriented crystallites for the MAPI and the MAPI/PEAMAPI samples, respectively. We find that around 33% of the crystals in the MAPI sample have a (002) orientation (c-axis perpendicular to the substrate), whereas about 40% of the crystallites are oriented in the MAPI/PEAMAPI sample. Integration over the (222) peak showed the typical profile of a Gaussian function, thus justifying the use of this function for amending the inaccessible area around the azimuthal angle χ = 0. The ratios of the integrated intensities agree very well for the (002) and (222) peaks with only slight deviations, which serve as an estimate for the uncertainty of the presented analysis. Assuming that the increase of oriented crystals is due to the formation of highly oriented PEAMAPI (as reasoned in the main text), 7.00±0.47% of the initial MAPI film is estimated to be converted into the LPK. 5
Figure S2. XRD pattern of a MAPI film treated with a 20 mm PEAI solution in isopropanol and powder XRD pattern of PEAI crystals. The absence of MAI in the casting solution leads to the crystallization of PEAI. Figure S3. XPS spectra indicating the C1s peaks of MAPI and MAPI/PEAMAPI films on glass. 6
Figure S4. GIWAXS data for a MAPI film and a MAPI/PEAMAPI bilayer film, integrated over the complete q range. The two distinct peaks at q 0.18 Å -1 and 0.41 Å -1 for the MAPI/PEAMAPI sample corroborate the formation of an oriented PEAMAPI perovskite layer. Figure S5. J-V curves of a MAPI/PEAMAPI heterojunction champion cell fabricated via an optimized MAPI deposition method. Recorded under simulated AM 1.5G illumination with 100 mw cm -2 (scan rate: 0.1 V s -1 ). 7
Figure S6. PCE as a function of time for a MAPI cell and a MAPI/PEAMAPI cell held to the maximum power voltage (~0.91 V reverse bias) under illumination. Figure S7. J-V curves of a MAPI control cell and MAPI/PEAMAPI devices prepared with different concentrations of the PEAI:MAI casting solution. Recorded under simulated AM 1.5G sun light and reverse bias sweep (scan rate 0.5 V s -1 ). 8
Figure S8. UV-Vis absorption spectra of a MAPI film and a MAPI/PEAMAPI film on glass, prepared with a 10 mm PEAI:MAI (1:1) solution. Figure S9. XPS spectra obtained for pure MAPI and a MAPI/PEAMAPI bilayer film. The left graph describes the energetic position of the valence band maximum (VBM) relative to the Fermi level E F. The graph on the right shows the energy difference between the secondary electron edge and the He I radiation, which corresponds to the work function. 9
Figure S10. Time-resolved PL decay for a MAPI and a MAPI/PEAMAPI film on glass analyzed by TCSPC. Figure S11. J-V hysteresis of photovoltaic devices comprising a MAPI/PEAMAPI, MAPI/BAMAPI or MAPI absorber layers. Recorded under simulated AM 1.5G sun light, reverse and forward bias scan (scan rate: 0.5 V s -1 ). 10
Figure S12. XRD patterns of a MAPI and a MAPI/PEAMAPI film before and after exposure to 75% RH for 2 h in air at room temperature. References 1. Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G. Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and near- Infrared Photoluminescent Properties. Inorg. Chem. 2013, 52, 9019-9038. 2. Langford, J. I.; Wilson, A. J. C. Scherrer after Sixty Years: A Survey and Some New Results in the Determination of Crystallite Size. J. Appl. Crystallogr. 1978, 11, 102-113. 3. Savaloni, H.; Gholipour-Shahraki, M.; Player, M. A. A Comparison of Different Methods for X-Ray Diffraction Line Broadening Analysis of Ti and Ag UHV Deposited Thin Films: Nanostructural Dependence on Substrate Temperature and Film Thickness. J. Phys. D: Appl. Phys. 2006, 39, 2231. 11