Supplementary Materials for

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1 advances.sciencemag.org/cgi/content/full/2/7/e16534/dc1 Supplementary Materials for Ultrahigh sensitivity of methylammonium lead tribromide perovskite single crystals to environmental gases Hong-Hua Fang, Sampson Adjokatse, Haotong Wei, Jie Yang, Graeme R. Blake, Jinsong Huang, Jacky Even, Maria Antonietta Loi Published 27 July 216, Sci. Adv. 2, e16534 (216) DOI: /sciadv The PDF file includes: fig. S1. Powder XRD pattern of crushed MAPbBr3 crystals. fig. S2. PL excitation spectrum and PL of a MAPbBr3 single crystal measured at room temperature in ambient air. fig. S3. Photostability of MAPbBr3 single crystal. fig. S4. PL spectra taken at different vacuum levels. fig. S5. PL spectra of crystals prepared by the AVC technique in vacuum and air. fig. S6. Steady-state and TRPL spectrum from a freshly cleaved crystal prepared by the ITC technique in vacuum and air. fig. S7. TRPL decay in vacuum from a crystal grown by ITC. fig. S8. PL intensity variation in different gases. fig. S9. Normalized PL spectra in different gases. fig. S1. PL intensity as a function of time in air under two-photon excitation (8 nm). fig. S11. Photocarrier distribution at t = under single- and two-photon excitation conditions. fig. S12. TRPL spectrum from a crystal prepared by the ITC technique under lower power density of 4-nm excitation. References (43 45) Other Supplementary Material for this manuscript includes the following: (available at advances.sciencemag.org/cgi/content/full/2/7/e16534/dc1) movie S1 (.mp4 format). Perovskite crystal under excitation of a 4-nm wavelength laser from an atmosphere of air to vacuum and then to air.

2 MAPbBr 3 PXRD Intensity (a.u.) Angle ( ) fig. S1. Powder XRD pattern of crushed MAPbBr3 crystals. PL Intensity (a.u.) 1. PLE PL Photon Energy (ev) PLE Intensity (a.u.) fig. S2. PL excitation spectrum and PL of a MAPbBr3 single crystal measured at room temperature in ambient air.

3 7 Photostability in Air 6 ± 2.5 % 5 67 PL Intensity (a.u.) Time (s) fig. S3. Photostability of MAPbBr3 single crystal. PL intensity as a function of illumination time at room temperature in ambient air. The excitation power is.71 J/cm 2. PL Intensity (Counts) Ambient Air 3E-3 mbar 3.4E-4 mbar 1.2E-4 mbar Wavelength (nm) fig. S4. PL spectra taken at different vacuum levels. The excitation power is.71 J/cm 2.

4 5 4 Air (Crystal by AVC) Vacuum PL Intensity Wavelength (nm) fig. S5. PL spectra of crystals prepared by the AVC technique in vacuum and air. The excitation wavelength is 4 nm and the excitation power is.71 J/cm 2. fig. S6. Steady-state and TRPL spectrum from a freshly cleaved crystal prepared by the ITC technique in vacuum and air. (A) PL spectra from a freshly cleaved crystal prepared by the ITC technique in vacuum and air under excitation of a 4 nm wavelength laser. (B) Decay of the photoluminescence in vacuum and air. The excitation power is.71 J/cm 2.

5 TRPL in vacuum PL Intensity (a.u.) 1 t 1 =2 ns; t 2 =22 ns Time (ns) fig. S7. TRPL decay in vacuum ( mbar) from a crystal grown by ITC. fig. S8. PL intensity variation in different gases. PL intensity variation (a) from an atmosphere of moist oxygen to vacuum and then to air; (b) from an atmosphere of dry oxygen to vacuum and then to air; (c) from an atmosphere of moist nitrogen to vacuum and then to air.

6 Normalized PL Intensity (a.u.) Wavelength (nm) Vacuum CO 2 He Ar N 2 H 2 O O 2 Air fig. S9. Normalized PL spectra in different gases. TPP PL intensity (%) Time (s) fig. S1. PL intensity as a function of time in air under two-photon excitation (8 nm).

7 Comparison of single-photon and two-photon absorption in MAPbBr3 single crystals In single-photon pumping, the absorption is governed by the well-known Lambert-Beer law. Thus the photoexcited carrier distribution is n(x) I(x) = I exp ( αx) (1) Here, I is the intensity of the incident light beam propagating along the z-axis, x is the distance from the crystal surface, and α is the one-photon absorption coefficient. In two-photon excitation, the absorption is proportional to a quadratic function of the laser intensity; where linear absorption is ignored, the penetration of the excitation is (43) di dx = βi2 (2) In this expression, I is the intensity of the incident light beam propagating along the x-axis, and is the two-photon absorption coefficient. Thus the photocarrier distribution at t = is n(x) I(x) = I 1+βI x (3)

8 Photocarrier density (a.u.) n = exp(- z) = 72 cm -1 n = 1/(1+ I z) b = 8.6 cm/gw I =.123 GW Distance from Surface ( m) fig. S11. Caculated photocarrier distribution at t = under single-photon (green) and two-photon (red) excitation conditions. In the two-photon condition, the laser power is about.123 GW, and the two-photon absorption coefficient is adopted from (44). The absorption coefficient of around 72 cm -1 at 4 nm is adopted from (3). PL Inensity (counts) Time ( s) fig. S12. TRPL decay of a crystal prepared by the ITC technique under 4-nm excitation. The fitted lifetimes are t1 =.8 s and t2 = 2.5 s. The excitation power is 1 nj/cm 2.

9 Surface recombination velocity in single crystals In order to extract the surface recombination velocity from the time-resolved PL, we used a simple one-dimensional diffusion model to describe the spatial and temporal behavior of the photogenerated carriers. The evolution of the carrier concentration n(x, t) is assumed to be governed by the diffusion equation (45) δn(x,t) δt =D 2 n(x,t) 2 x n(x,t) τ + G, (x ) (4) and boundary conditions n(, t) = D S δn(x,t) δx, (on x = ) (5) The initial carrier distribution deposited by pulse laser is given by n(x, ) = n e αx (6) where x is the distance from the surface, t is the delay time, D is the ambipolar diffusion constant, and is the absorption coefficient at the excitation wavelength. A Fourier integral is a solution of equation (4) n(x, t) = e t τ e k 2 Dt A(k)(cos kx + S sinkx)dk (7) αd

10 where A(k) = 2n (α+s/d)k 2 π(a 2 +k 2 )( S2 D 2+k2 ) (8) The effective lifetime can be determined by solving the continuity equation for the carrier concentration profile, leading to the following expression (31) 1 = 1 2α + 2 D (9) τ τ b α 2 D 2 /S 2 Numerical Simulation of Photocarrier Distribution and PL Spectrum The photocarrier distribution in a single crystal is calculated by the carrier diffusion equation above. D is the diffusion coefficient and is related to the photocarrier mobility μ. According to the Einstein relation, D = μkt/q. In the calculation S = 4cm/s is used. The initial photocarrier distribution is n(x) = n exp ( αx). The normalized, time-dependent PL intensity from the crystal is written in terms of an integral (45) I λ (t) = n(x, t) 2 exp ( α λ x) dx (1) where n(x,t) is the photocarrier distribution at time t and α λ is the absorption coefficient at wavelength λ.