Supporting information

Transcription

1 Supporting information Determination of Thermal Expansion Coefficients and Locating the Temperature Induced Phase Transition in Methyl Ammonium Lead Perovskites using X-Ray Diffraction T. Jesper Jacobsson 1 *, L. Josef Schwan 2, Mikael Ottosson 2, Anders Hagfeldt 1,2, and Tomas Edvinsson 2 1) Laboratory for Photomolecular Science, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, CH-1015-Lausanne, Switzerland 2) Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, Uppsala, Sweden Jesper.jacobsson@epfl.ch, +46 (0) ~S1~

2 Theory (a) (b) Figure S.1. Simulated XRD diffractogram for (a) the cubic methyl ammonium lead iodine perovskite, and (b) the corresponding tetragonal phase. Experimental XRD data Figure S.2. Comparison between spin coated and drop coated films. Data have been normalized with respect to the most intense peak. (a) (b) Figure S.3. (a) Comparison between XRD data for the synthesized perovskite and for the methyl ammonium precursor. (b) Comparison between perovskite and PbI 2. ~S2~

3 Figure S.4. A Gaussian peak fit for the fifteen groups of peaks analyzed, here illustrated for the XRD data at 35 C which was the first temperature measured. ~S3~

4 UV-VIS UV-vis absorption was measured on the spin coated films, and data for a typical sample is given in figure S.5. As is evident from the figure, as well as the photograph of the film shown in the inset (S.5.b), the film is highly scattering, making it difficult to extract quantitative information from the absorption data. By using more elaborate film deposition procedures, semi-transparent films with a higher macroscopic optical quality can be achieved, but as the focus in this work has been on crystallographic properties, which are not affected by light scattering due to macroscopic irregularities, this has not been prioritized. The optical band gap was determined from the absorption data. This was done by subtracting the background caused by scattering, as in figure S.5.c, and thereafter plotting the square of the absorption against photon energy as in figure S.5.d. For direct semiconductors, extrapolation of the linear region, as shown in figure S.5.d, gives the band gap as the intercept with the baseline. For the spin-coated films a band gap of 1.54 ev was obtained, which is well in line with what has been reported for polycrystalline films 1, 2. There is, however, a fair amount of uncertainty to this value due to problems related to subtraction of the high background caused by the light scattering. The measured absorption decreases somewhat for higher photon energies. This is likely a result of the variations in the background level due to scattering from surface irregularities in the film. This is not affecting the determination of the band edge but interpretation of optical properties at higher energies should be taken with care due to the strong influence of scattering in the data. Figure S.5. (a) UV-vis absorption of spin coated CH 3 NH 3 PbI 3 film. (b) Photograph of the film on a substrate with an UU-logo beneath (can be seen faintly through the film) the film. (c) UV-vis absorption with the background removed. (d) Square of absorption against photon energy; the band gap is extracted as the intercept of the straight line and the baseline. ~S4~

5 Additional UV-vis and photoluminescence data The absorption data in the previous section deviate somewhat from what could be expected. New films where therefor deposited at a later stage on which new optical measurements were made. Three different deposition protocols were employed. One used spin coating, but with the lately widely applied anti-solvent approach which give films of more uniform morphology and with higher optical quality, which in the end provide better device performance. With this deposition method, and these solution parameters, we have manufactured devices with over 15 % efficiency, which will be discussed in other papers. The second film is deposited directly form the precursor solution without the use of an anti-solvent. That film is equivalent to the spin coated films used for the XRD measurements discussed in the article. The last films are drop coated and correspond to the films on which the temperature dependent XRD measurements were performed. A photo of these films is given in figure S.7. Absorption data for these films, measured with a UV-vis setup different from than used for the data in figure S.5, is given in figure S.6.a. The scattering for the solvent engineered film is reasonable low compare to previous data, whereas the scattering for the second spin coated film and the drop coated film is high. This UV-vis setup provides more reasonable spectra for higher photon energies. The band gaps are extracted after back ground removal in figure S.6.b. The band gap is determined to 1.6 ev for all films. That is a reasonable value given what has been reported in the literature. It is also fairly close to the values given form the data in figure S.5. This furthers illustrate the extracted data for the band gap to rather insensitive to the back ground removal procedure. In figure S.6.c, steady state photoluminescence data is given for these three films. They all show the same appearance even though they differ somewhat in absolute intensity. In all three cases, one strong peak is obtained at 764 nm which is slightly higher than the band gap energy. This indicates the films to be of reasonably high crystallographic quality and that the dominant radiative loss mechanism is a transition from the conduction band edge to the valence band edge. (a) (b) (c) Figure S.6. (a) Absorption data on a second set of films. Both spin coated and drop coated. (b) Extraction of band gaps after back ground removal of the absorption data in (a). (c) Steady state photoluminescence for the same set of films Figure S.7. A photo of the set of films which absorption and PL data are found in figure S.6. (a) Spin coated film using the anti-solvent method. (b) spin coated film directly from the precursor solution. (c) A thicker drop coated film. ~S5~

6 Table S.1. Simulated XRD data for cubic structure. Full table Peak d-spacing Intensity number 2θ [ ] [Å] Scaled F h k l Mult, 1 14,021 6, , ,878 4,4629 7,05 33, ,408 3, ,37 69, ,257 3, ,55 212, ,674 2, ,47 111, ,674 2, ,47 111, ,789 2,5767 3,7 30, ,388 2, ,19 193, ,956 2,1038 6,51 103, ,956 2, ,03 103, ,405 1,9959 0,91 29, ,405 1,9959 0,91 29, ,755 1,903 5,62 54, ,021 1,822 18,69 180, ,214 1,7505 7,45 97, ,214 1,7505 7,45 97, ,343 1,6868 1,09 27, ,343 1,6868 1,09 27, ,443 1,5779 8,79 170, ,426 1,5308 4,85 92, ,426 1,5308 4,85 92, ,426 1,5308 9,69 92, ,37 1,4876 0,73 26, ,37 1,4876 0,37 26, ,28 1,448 2,18 47, ,16 1, ,13 162, ,16 1, ,13 162, ,013 1,3773 6,86 88, ,013 1,3773 6,86 88, ,843 1,3456 0,53 25, ,44 1, , ,213 1,2623 1,3 85, ,213 1,2623 2,6 85, ,213 1,2623 2,6 85, ,972 1,2378 0,21 24, ,972 1,2378 0,21 24, ,972 1,2378 0,41 24, ,972 1,2378 0,41 24, ,718 1,2146 1,2 42, ,718 1,2146 0,4 42, ,18 1,172 2,09 82, ,18 1,172 2,09 82, ,18 1,172 4,19 82, ,18 1,172 4,19 82, ~S6~

7 45 83,9 1,1523 0,34 23, ,9 1,1523 0,34 23, ,324 1,1157 5,95 143, ,032 1,0987 3,57 79, ,032 1,0987 3,57 79, ~S7~

8 Table S.2. Simulated XRD data for the tetragonal phase 2θ d-spacing Int. No. [ ] [Å] Scaled F h k l Mult ~S8~

9 ~S9~

10 ~S10~

11 References (1) 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.; Gratzel, M.; Park, N. G., Sci. Rep. 2012, 2, 1-7. (2) Dang, Y. Y.; Liu, Y.; Sun, Y. X.; Yuan, D. S.; Liu, X. L.; Lu, W. Q.; Liu, G. F.; Xia, H. B.; Tao, X. T., Crystengcomm 2015, 17, ~S11~