Supplementary information: X-ray stability and degradation mechanism of lead halide perovskites and lead halides

Supplementary information: X-ray stability and degradation mechanism of lead halide perovskites and lead halides Sebastian Svanström1, Alberto Garcia Fernandez2, Tamara Sloboda2, T. Jesper Jacobsson3, Håkan Rensmo1, Ute B. Cappel2* 1: Division of X-ray Photon Science, Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20, Uppsala, Sweden 2: Division of Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden 3: Young Investigator Group Hybrid Materials Formation and Scaling, Helmholtz-Zentrum Berlin für Materialen und Energie GmbH, Albert-Einstein Straße 16, 12489 Berlin, Germany * cappel@kth.se


Model for heating induced by an elliptical photon beam
The incoming power of a monochromatic photon (X-ray, UV or laser) beam can be calculated by Nph is the number of photons per second, e is the charge of the electron (1.60x10 -19 C) and Eph is the photon energy (in eV). This power input needs to be balanced by heat losses from the spot. The heat losses can be divided into two types, radiative and conductive.
The radiative losses can be calculated by assuming that both the spot and the surrounding are black bodies which allows the radiative balance to be calculated using where σ is Stefan-Boltzmann constant (5.67x10 -8 W m -2 K -4 ), Tspot is the temperature of the spot, Tamb is the ambient temperature (20 o C), and Aspot is the area of the spot which for an ellipse is ( !"#$ = ) where a is the width of the spot and b is the length of the spot. The conduction losses in the substrate of an elliptical spot can be estimate by (half of) the heat conduction from an ellipsoid in an infinite medium, shown in Figure S1. The heat losses from this shape can be calculated using ,'-% = ./0(2 !"#$ 32 %&' )5637 ( /9 ( $#,($-" 5637 ( /9 ( where k is the heat conductivity (W/mK) of the substrate 1 , in this case glass (0.8 W/m 2 ). This model requires that the width of the spot (a) is significantly larger than thickness of the thin film but significantly smaller than the thickness of the substrate. However, if the conductivity of the substrate is lower than of the surface to which it is mounted this calculation will still give a higher limit of the temperature. To calculate the temperature of the spot the energy balance can be calculated using and solved for Tspot. The spot dimensions, maximum X-ray power and the resulting spot temperature (the ambient temperature is 20 o C) in the three measurement is shown in Table S3. Core to core binding energy differences

Organic lead halide perovskites
Spectrum and chemical ratios  Figure S4b.

Analysis of degradation kinetics
The I -/Pb 2+ , N(FA)/Pb 2+ and C(FA)/Pb 2+ ratios determined from measurements at all X-ray flux densities, of the CsFA-I, CsFA-Mix and MAFA-Mix samples were fitted with an exponential decay, shown in Equation 1. The resulting parameters, as well as the initial ratios R(0), are shown in Table S5 and the fits are shown in figure S6.
were R0 is the change in ratio due to irradiation, R∞ is the ratio after complete decay and kr is the radiolysis constant of the decay. In the case of N(FA + )/Pb 2+ , C(FA + )/Pb 2+ the ratio after complete decay is fixed to 0.  Chemical ratios vs. fluence

CsPbBr 3
Spectrum and example fits Figure S9 shows the Cs3d and Pb4f core levels while Figure S10 shows the C1s, Cs4d, Br3d, Pb5d core levels and valence band (Fermi level enlarged) of the CsPbBr3 sample normalised and calibrated against total Pb4f signal intensity. Figure S11 show an example of the curve fits of Pb4f, Cs4d and Br3d after degradation has begun. Figure S12 shows the ratio of the initial components (Cs + , Brand Pb2 + ) and the new components (CsNew, BrNew and Pb 0 ) as a function of time and fluence. Figure S13a shows the ratio between the new Br3d and Cs4d components of the CsPbBr3 sample. Figure S13b shows the Cs + /Pb 2+ and Br -/Pb 2+ ratio in the CsPbBr3 sample as a function of time and fluence. Table  S6 show the binding energies and core to core binding energy differences of the CsBr reference sample. Figure S14 show the fits of the Cs3d, Cs4d and Br3d core levels of the CsBr reference sample.