Anisotropic carrier dynamics and laser-fabricated luminescent patterns on oriented single-crystal perovskite wafers

Perovskite materials and their applications in optoelectronics have attracted intensive attentions in recent years. However, in-depth understanding about their anisotropic behavior in ultrafast carrier dynamics is still lacking. Here we explore the ultrafast dynamical evolution of photo-excited carriers and photoluminescence based on differently-oriented MAPbBr3 wafers. The distinct in-plane polarization of carrier relaxation dynamics of the (100), (110) and (111) wafers and their out-of-plane anisotropy in a picosecond time scale were found by femtosecond time- and polarization-resolved transient transmission measurements, indicating the relaxation process dominated by optical/acoustic phonon interaction is related to photoinduced transient structure rearrangements. Femtosecond laser two-photon fabricated patterns exhibit three orders of magnitude enhancement of emission due to the formation of tentacle-like microstructures. Such a ultrafast dynamic study carried on differently-oriented crystal wafers is believed to provide a deep insight about the photophysical process of perovskites and to be helpful for developing polarization-sensitive and ultrafast-response optoelectronic devices.


Table of Contents
Table S2.Probe polarization dependence fitting for carrier relaxation dynamics in MAPbBr3 (100) wafer.
Table S4.Probe polarization dependence fitting for carrier relaxation dynamics in MAPbBr3 (111) wafer.In order to prove the high quality of the grown MAPbBr3 crystal, we have performed highresolution X-ray diffraction (HRXRD) on the three single crystal wafers.Figure S1a shows the rocking curves in a θ scan mode.We can see the MAPbBr3 crystal wafers show an FWHM (full width at half-maximum) of 60.19 arcsec for (100), 40.28 arcsec for (110), and 86.72 arcsec for (111).As we all known that the FWHM of HRXRD or the X-ray diffraction rocking curve is an important index to evaluate crystalline quality of single crystals, wherein a perfect crystal produces a symmetrical and sharp peak profile with a small FWHM.Here our measured FWHM are much smaller than the reported values for MAPbBr3 crystals [1][2][3] , and is even comparable with those of the well-developed inorganic crystals 4 , demonstrating the grown crystals possessing high crystalline perfection.Furthermore, we have also measured the X-ray Laue diffraction patterns of the MAPbBr3 wafers.As shown in Figure S1b, the well-defined laue diffractions further confirm the high crystal quality of the MAPbBr3 wafers.crystals (with the thickness in millimeters and above), which is attributed to the non-degenerate two-photon absorption (TPA) when the pump and probe beams overlap both temporally and spatially.

Figure S9
. The relaxation dynamics of free carriers and excitons were investigated before and after laser processing, with probing wavelengths of 555 nm and 800 nm, respectively.

Supplementary Note 1. The analyzation of photogenerated excitons dynamics
It has been reported that there should be two kinds of primary photoexcitations in the hybrid perovskites, namely free carriers in the valence band (VB) and/or conduction band (CB); and excitons which are Coulomb correlated electron-hole (e-h) bound pairs.The reported exciton binding energy of MAPbBr3 perovskite ranges from 40 to 150 meV, [5][6][7] larger than the thermal energy (∼26 meV) at room temperature.][10] ("with typical excitation densities of around 10 16 -10 17 cm −3 for PL quenching experiments, free carrier population is found to be in the range of ≈50%-90% when trap states are not considered."Tze Chien Sum et al., Adv.Energy Mater. 2016, 1600551) Additionally, according to the reference suggested by the reviewer below (Nat.Photonics 2015, 9, 695), it is reported that the electrostatic potential variations in smaller polycrystals suppress exciton formation, while the larger single-crystals of the same composition demonstrate an unambiguous excitonic state.
In our work the relaxation dynamics of the excited-carriers in the picoseconds timescale was monitored by using a polarized probe pulse at 1.55 eV, following an above-bandgap pump ).According to the TA spectra (Figure S10a), there is observed an obvious positive ∆A signal, signifying the occurrence of photoinduced absorption (PA) in the broad spectral region of λ >600 nm (Figure S10b).The PA signal became stronger as the excitation density increased (Figure S10c), which confirms that it should mainly originate from the excited hot carriers.Here, we ascribe the negative ∆A signals close to the optical gap as the ground-state bleaching (GSB), which is attributed to state-filling by excited carriers.However, it is evident that the dynamic of PA is different from that of the bleaching band, as shown in the  However, the authors of [Adv.Energy Mater. 2016, 6, 1600551] considered the PA band "possibly arises from the transitions of the photoexcited species to higher excited states or subbandgap trap state absorption in the crystal, which is significant in the very thick crystal (≈ 3.2 mm) while negligible in the thin film (≈100 nm)"; and the authors of [Adv.Optical Mater.2018, 6, 1700975] concluded that "While we cannot eliminate all other mechanisms, we believe that polaron formation is the most likely hypothesis for our TA observation in perovskite bulk single crystals."The above reports demonstrate that there is indeed divergence on the assignment of the PA band.Here given the low amplitude and longer lifetime of the PA band, and the "soft" lattice nature of MAPbBr3 crystal, it is more likely that free carriers, excitons, and polarons coexist in the photogenerated states.
Whatever, at present all the assignments of the longer wavelength PA band are short of direct and solid evidence.In fact, even the exact band structures and the actual fundamental band-gap values of such hybrid perovskites are still under intense debate in the computational community.[J.Phys.Chem.Lett.2017, 8, 5507; J. Chem.Theory.Comput.2016, 12, 3523] To quantitatively assign the features in the TA spectra to specific transitions through theoretical calculations is infeasible.Thus although it is considered that exciton absorption is a most likely hypothesis for the observed longer wavelength PA in perovskite bulk single crystals, we cannot eliminate the possibilities from other attributions such as polarons or other sub-bandgap trap state absorption.And the predictability of the specific transitions necessitates more detailed experimental and theoretical investigations in this field.

Supplementary Note 2. Anisotropic relaxation dynamics evolution of free carriers in MAPbBr3
The polarization anisotropy detected at the wavelength of 800 nm, which may predominantly reflect the selection rules between excitonic states rather than those of free carriers.Therefore, based on the transient absorption spectra of MAPbBr3 crystals (Figure S4), we measured the dynamics at a wavelength of 575 nm that located on the bleaching band, to better capture the relaxation processes of free carriers.
The carrier dynamics probing at 575 nm on differently-oriented MAPbBr3 wafers were conducted with the same test conditions as that in 800 nm detections (a 3.1 eV femtosecond pump laser and a pump fluence of 71 μJ cm -2 ).The bleaching dynamics at 575 nm (shown in the insets of Figure S11) can also be fitted well by two shorter lifetimes: τ1 within ~ 20 ps and τ2 within ~ 150 ps, and another longer lifetime, τ3, being fitted at the nanosecond scale.The overall time scale of the bleaching dynamics is slightly longer than that of the PA dynamics, but the time of peak occurrence is almost identical to the PA band, both around 1.5 ps, corresponding to the electron-electron scattering and electron-longitudinal optical (LO) phonon scattering.

Figure S11. Anisotropic relaxation dynamics evolution of MAPbBr3 probed at 575 nm.
Figure S11 shows the pseudo-color polarization-resolved transient absorption plots of the bleaching dynamics at 575 nm on the (100), ( 110) and (111) wafers.As can be seen for each stage of the carrier dynamics, including the extremely fast cooling stage represented by the peak value of ΔA, and the two decay stages represented by the lifetimes (τ1 and τ2), they indeed demonstrated obvious angle-dependence upon variation of the probe polarizations.Compared to the anisotropy of dynamics probed at 800 nm, the anisotropic behaviors probed at 575 nm shows similar polarization-dependent symmetry, with a milder contrast among different orientations.Compared to free carriers, excitons should possess relative more localized nature in crystal, thus stronger interactions with the lattice and phonons during the relaxation process should be anticipated, which makes them more susceptible to the influence of the lattice structure.On the one hand, the additional subtle variations may be caused by inevitable light disturbances owing to the close proximity of signals at different polarization angles during measurements.
Overall, the dynamics probing at the beaching band of 575 nm should reflect more information about free carriers of the excited state of MAPbBr3.Although there are some differences in the relaxation lifetimes and polarization-dependent symmetry patterns, both the dynamics of free carriers and excitons exhibit obvious in-plane polarization dependence on (100) and (111) wafers while a weak dependence on the (110) wafer.Because the relaxation processes for both the two types of particles involve interactions with lattice vibrations (phonons) in the decay to lower energy levels or the ground state, they are influenced by the intrinsic factors such as the symmetry of electronic band structure, phonon spectra, and other lattice-related elements.Therefore, similar selection rules may take effect during the relaxation process regardless of the particle type.

Supplementary Note 3. The long-range Fröhlich interaction in MAPbBr3
As we know, the Fröhlich model addresses the electrons in ionic crystals or polar semiconductors. 12The strength of the Fröhlich interaction in a material is directly linked to the polar nature of its crystal lattice.In a highly polar material the Coulomb field of a carrier (or exciton) couples more easily to the polar vibrations (i.e.LO phonons) of the lattice, resulting in strong Fröhlich coupling.In the structure of MAPbBr3 crystal, it consists of two interpenetrating sublattices: an inorganic lattice composed of corner-shared PbBr6 4− octahedral and a second sublattice composed of MA + cations.The non-superimposed arrangement of the positive and negative charges leads to the existence of electric dipoles in the lattice and makes the perovskite lattice polar.Due to the polar nature of MAPbBr3, Fröhlich interaction is the dominant relaxation pathway for hot carriers, wherein the electron-longitudinal optical (LO) phonon scattering arises from Coulomb interactions between the electrons and the macroscopic electric field induced by LO phonon mode.Thus the Fröhlich interaction that governs electronlattice coupling is considered to be long-range interaction.[15][16] The electron-phonon interactions lead to the formation of a polaron state, where an electron or a hole deforms the lattice in its vicinity and becomes more localized. 17To date, the conventional Fröhlich interaction has been mainly considered to be the polaron formation mechanism in halide perovskites.Depending on the range and strength of the electron−phonon interaction, polarons can be generally categorized into large and small polarons.For the 3D lead halide perovskites, large polarons are formed by the long-range electron-LO phonon interaction, i.e., the charge carriers coupling to the vibrational motion of the inorganic lattice, while the A site cation only plays a minor and indirect role by affecting the distortion of the inorganic lattice.(Conversely, a small polaron is formed by strong and short-range electron−phonon interactions and is usually localized within a single lattice constant.Small polarons are mostly revealed in the low-dimensional halide perovskites and double perovskites.The Fröhlich interaction model is inapplicable to the strong electron−phonon coupling of small polarons.) 9][20] In particular, Zhu et al. 21have provided a direct time domain view of large polaron formation in single-crystal MAPbBr3 and CsPbBr3 using time-resolved optical Kerr effect (TR-OKE) spectroscopy and in conjunction with hybrid density functional theory (DFT) calculations, obtaining the electron and hole polaron mobilities of μe = 149.8cm 2 V −1 s −1 and μh = 79.2cm 2 V −1 s −1 with corresponding polaron radii of ρe = 4.18 nm and ρh = 3.13 nm in MAPbBr3.Lindenberg et al. 22 visualized excitation-induced strain fields in MAPbBr3 via femtosecond resolution diffuse X-ray scattering measurements, confirming the formation of large polarons with a polaron radius of ~3 nm at t = 20 ps.Consequently, the observation of large polarons, which extend over more than a few lattice sites, provides further evidence supporting the existence of long-range Fröhlich interaction in MAPbBr3 crystals.About whether the interaction strength will differ along different planes, because the electron−phonon scattering relates to carrier effective mass, LO phonon energy, and dielectric constant, we could find the dependence between crystallographic planes and the strength of electron-phonon coupling interaction according to the so-called Fröhlich constant α is defined by, 23 = ħ 1 −

2ħ
Where ε∞ and εs are optical and static dielectric constants, respectively, m is the effective mass of the electron in the case of no electron-phonon interaction (bare band mass), and describes the LO phonon frequency.
The quantity = − , which is known as the dielectric contrast, quantifies the ionic nature of a material and thereby determines the strength of the carrier-lattice interaction.Consequently, the static and high-frequency values of the dielectric function provide a means of evaluating the Fröhlich interaction among differently oriented planes.
Thus we analyzed the dielectric function of differently oriented MAPbBr3 wafers by measurements of the refractive index (k) and the extinction coefficient (n) through a spectroscopic ellipsometry (SE) method.(Figure S12a & b) The complex refractive index, N = n − ik, contains the same information as the dielectric function, ε = ε1 − iε2, with ε1 = n 2 − k 2 and ε2 = 2nk. 24By analysis of n and k as a function of wavelength, it is notable that for both real (ε1) and imaginary (ε2) dielectric function in the optical region, the values indeed show discrepancies for differently oriented wafers.(Figure S12c & d) Deducing from the dielectric mechanism, the dielectric contrast should be even larger in the low-frequency THz region where the LO phonons typically reside.Therefore, on account of the measured ε1(110) > ε1 (100) > ε1 (111), the difference of dielectric function on different crystal planes will definitely affect the Fröhlich interaction strength along different planes.

Supplementary Note 4. The analyzation of correlation of polarization-dependent dynamics to the crystal structure
The in-plane polarization-dependent dynamics on the (100) and (111) wafers and the isotropic dynamics on the (110) wafer represent one of the most prominent discovery revealed by this study.In the current experiment, the relaxation time scale mainly concerns the carrier dynamics involving hot carrier cooling, polaron formation, exciton formation, and the subsequent dynamics of "cold" carriers near the band-edge involving photoinduced lattice expansion, strain, and coherent phonon effects.During these photophysical processes, the carrier−phonon interaction plays a significant role by inducing local lattice displacements which generate a polarization-induced electric field that in turn interacts with the charge carriers.Thus the involvement of phonons (lattice vibrations) in all these stages corelates the carrier relaxation dynamics with the lattice structure.
7][28][29] These recent investigations unambiguously corroborated the steady-state anisotropy on MAPbBr3 single crystals, however, the transient-state anisotropy in the ultrafast carrier dynamics still remains sealed.This is because the anisotropy of steady-state properties relies directly on the static crystal structure that we can depict intuitively; while for the ultrafast carrier dynamics occurring in the excited state, there are two main obstacles.Firstly, photoexcitation can lead to a distinct excited electronic structure compared to the ground state (so far, there is still a big challenge to accurately capture the excited electronic structures experimentally).Secondly, the carrier relaxation process is heavily influenced by phonons, which are hard to describe with a clear picture.Therefore, it is infeasible to directly corelate the carrier relaxation dynamics with the electronic structure of the ground state.In spite of these challenges, we can still find clues from analyzing the distortion of the PbBr6 octahedral framework and the dynamic orientation of MA + cations.Additionally, investigating the defect density distribution along different crystallographic orientations and considering the surface and many-body effects can provide further understanding.These factors may affect the excited electronic structure and phonon behavior of MAPbBr3 single crystal.
Lattice deformation, vibration and relaxation effect: Because of the different crystallographic geometric configurations of the (100), ( 110) and (111) planes (Figure S1, including the atomic density, interplanar spacing, etc.) and the distribution of MA + orientation domains, the equilibrium out-of-plane and in-plane anisotropic structure should induce non-synchronized lattice deformation and relaxation upon photoexcitation, which may break the original lattice symmetry in the excited state structure.E.g., the MA + rocking and twisting vibration modes demonstrate distinct in-plane anisotropy on (100) and (110) wafers, which may in turn cause interactions on the distortion of the PbBr6 4− inorganic skeletons; and the transient photoluminescence lifetimes also show discrepancies among (100), ( 110) and (111) wafers. 26onsequently the incoherent lattice vibration amplitude and frequency dictate the specific phonon modes along different crystallographic orientations in MAPbBr3.Thus an azimuthally balanced lattice deformation on the (110) plane is imagined to induce a polarizationindependent excited state dynamics on the (110) crystal plane.
Trap density distribution and surface effect: Because on the different crystallographic planes, the defect formation energies of vacancies and interstitials are different; and likewise, the ion migration also depends on the crystallographic orientations, these will lead trap density distributions inhomogeneously on different crystal wafers.By using space charge limited current (SCLC) measurements performed on (100), (110) and (111) wafers, we have demonstrated the discrepancy of trap densities on differently oriented wafers. 27Carrier scattering and trapping resulting from defects play a crucial role in influencing carrier relaxation in different orientations within the bulk crystal.Additionally, the polaronic nature of the relatively soft lattice in MAPbBr3 introduces surface dipoles that affect electronic structure and charge distribution.These factors also become significant determinants of carrier transport and recombination properties on distinct crystal planes.Thus a more highly symmetrical distribution of the excited-state charge density on the (110) crystal plane is anticipated.
Many-body effect: The interactions among electrons and with other particles, such as phonons (lattice vibrations) and other carriers, can lead to many-body effects.These effects cause a redistribution of momentum and energy of the excited state electrons through energy exchange or resonance coupling between the particles.Many-body effect has significant consequences on the carrier's lifetime and optical properties such as absorption and refraction in the excited state, thus making the carrier dynamics even more complicated.
Therefore, due to the uncomparable excited state electronic structure with that of the ground state, the mechanisms behind ultrafast hot carrier relaxation process are too subtle to be accurately learned.Frankly speaking, we still do not have exact answers about why MAPbBr3 (110) wafer behaves distinctly in the excited-state carrier relaxations compared to other wafers.It is important to note that it requires more detailed experimental investigation and deeper analysis to correlate the observed polarization-dependent dynamics with the crystallographic structures in different crystal planes.This study, based on the differently-oriented MAPbBr3 single-crystal wafers, firstly penetrated into the orientation-dependent dynamical evolution of the excited carriers and provided solid observations of the anisotropy in the ultrafast carrier dynamics.Although a comprehensive understanding has not been achieved yet due to limitations in excited-state experimental techniques, this discovery holds significant implications as it provides a novel perspective for a deeper understanding of the ultrafast carrier relaxation pathways and opens up new possibilities for utilizing perovskite single crystals in polarization-sensitive photoelectron responses.In Figure S13, we show the experimental steady-state PLQY data as a function of excitation density of MAPbBr3 crystals before and after processing, respectively.We note that the pristine MAPbBr3 (unprocessed bulk crystal) exhibits a very low PLQY of <0.1% under the measurement conditions with excitation densities lower than 10 16 cm −3 .While the processed crystal shows a much higher quantum yield in the order of ten percent at similar densities (and under ambient atmosphere).We find that the PLQY of the pristine MAPbBr3 crystal shows an upward change at high excitation fluences.This trend is consistent with the model described in ref [Phys.Rev. Appl.2014, 2, 034007] that the charge-trapping pathways limit the radiative recombination at low excitation fluences, and the radiation would be significantly enhanced when the charge trap states are filled by photogenerated carriers at higher excitation fluences.Additionally, we have confirmed the presence of metallic Pb(0) defect in the pristine bulk MAPbBr3 and its transformation into oxygen passivated-Pb(II) after laser processing by X-ray photoelectron spectroscopy (XPS).Because the excess Pb(0) atoms have been proved to act as deep defect levels that cause nonradiative decay to degrade the photoluminescence, it is suggested that its transformation into the oxygen passivated-Pb(II) corresponds to a transition from nonradiative deep-level traps to radiative shallow traps after laser processing.According to the model described in ref [J.Am.Chem.Soc.2016, 138, 13604], the participation of shallow defects in the radiative process leads to an increased PLQY compared to the case of deep trap states.Our PLQY measurements show a pronounced increase from the pristine crystal to the laser-processed one, indicating the formation of shallow-trap states by induction of femtosecond laser and/or passivation of the deep-level traps by ambient oxygen.Due to the limit of the power of excitation light source, the excitation intensity-dependence of the measured PLQYs for both the pristine and processed MAPbBr3 remain pretty insensitive at the lower excitation intensity range (<10 16 cm -3 ).However, a slight enhancement of the PLQY was still observed on the pristine crystal at higher excitation intensity.This slight increase of PLQY may be attributed to the increased filling of trap states and, possibly, to an increasing excitonic fraction of photogenerated species at higher excitation intensity.[Phys.Rev. Appl.2014, 2, 034007] It's reported the substantial increase of PLQY for the case of shallow traps may occur at even higher excitation intensity due to the high depopulation rate Rdep of the trapped carriers compared to that of the deep traps.[J. Am.Chem.Soc.2016, 138, 13604] It is noted that due to the fact that the measured PLQY of the pristine crystal is quite low, even within the degree of measurement error, the conclusion is indeed lack of solid evidences.

Supplementary Note 5. The analyzation of intensity-dependent PLQYs and TA spectra
The involvement of different types of defects is also supported by the intensity-dependent TAS measurements.

Figure S2 .
Figure S2.The in-plane and out-of-plane views of MAPbBr3 crystal structure.

Figure S3 .
Figure S3.Schematic illustration of the angle-resolved transient transmission apparatus.

Figure S4 .
Figure S4.Pseudo colour TA plots of MAPbBr3 with 400 nm excitation and 515 nm excitation.

Figure S5 .
Figure S5.Schematic illustration of the transmission open-aperture Z-scan technique.

Figure S7 .
Figure S7.Effect of processing scanning speed on luminescence.

Figure S8 .
Figure S8.Pseudo colour TA plot of MAPbBr3 (100) wafer is plotted by logarithmic delay time.

Figure S9 .
Figure S9.The relaxation dynamics of free carriers and excitons before and after laser processing.

Figure S13 .
Figure S13.The intensity-dependent PLQYs of MAPbBr3 crystals before and after processing as a function of charge density.

Figure S14 .
Figure S14.Pseudo colour TA plots and TA spectra on untreated MAPbBr3 wafer at different excitation densities.

Figure S15 .
Figure S15.TA spectra at different excitation densities at 1.5 ps of processed MAPbBr3 crystals.

Figure S2 .Figure S3 .
Figure S2.The in-plane and out-of-plane views of MAPbBr3 crystal structure with different orientations.The in-plane (top) views of the MAPbBr3 crystal structure reveal twodimensional arrangements forming a continuous network.The out-of-plane (side) views of the MAPbBr3 crystal structure display the stacking of (100), (110), and (111) planes, respectively, resulting in three-dimensional arrangements.

Figure S5 .
Figure S5.Schematic illustration of the transmission open-aperture Z-scan technique.The experiment is carried by moving the sample back-and-forth from the focal point of the pulsed laser beam along its optical axis (defined as the z-axis).

Figure S6 .
Figure S6.The scanning electron microscope (SEM) images of femtosecond laser processed scalable patterns on three MAPbBr3 wafers.[laser power: 5 mW, defocus: 470 μm and scanning speed: 0.1 mm s -1 ] Free carrier dynamic for unprocessed MAPbBr 3 crystal Free carrier dynamic for processed MAPbBr 3 crystal Exciton dynamic for unprocessed MAPbBr 3 crystal Exciton dynamic for processed MAPbBr 3 crystal at 3.1 eV (the energy bandgap of MAPbBr3 single crystal is ∼2.3 eV) with low excitation density (1.4×10 15 cm-3

Figure S10d ,
indicating that these two bands originate from different photoexcitations.We therefore assign the PA band to reflect dynamics of the photogenerated excitons.The observation is consistent with the investigation by Anita Ho-Baillie et al. [J.Phys.Chem.C 2016, 120, 2542] that "The much faster rise of PA2 indicates a different origin from bleaching, which is most likely to be the absorption of photogenerated excitons for several reasons."Sheng et al. [PRL 2015 114, 116601] also attributed a similar absorption band after photoexcitation of MAPbPbI3 to generation of exciton.When assuming the PA band around ~ 750 nm was attributed to exciton absorption, it's important to relate the exciton PA to specific transitions between distinct excitonic states.For MAPbBr3, the EI and EIII exciton states, separated by an energy of ∼1.642 eV [Solid State Commun.2003, 127, 619], coincidently corresponds to the PA band at ∼750 nm (∼1.650 eV) in the TAS.Hence, it is reasonable to speculate that the PA band is attributed to the inter-band exciton absorbing transition (EI to EIII).

Figure S10 .
Figure S10.The analyzation of photogenerated excitons dynamics.(a) Pseudo colour TA plot with the excitation density of 1.45×10 16 cm -3 .(b) TA spectrum at different delay time.(c) TA spectrum at different excitation densities at 1.5 ps.(d) The ground-state bleaching (GSB) and photoinduced absorption (PA) dynamics are probed at 555 nm and 800 nm, respectively.

Figure S13 .
Figure S13.The intensity-dependent PLQYs of MAPbBr3 crystals before and after processing as a function of charge density.

Figure
photogenerated excitons may keep in a relatively steady level with increasing of the excitation fluences.This observation is further corroborated by the redshift in the bleaching band compared to the pristine crystal.The authors of [JPCC 2016, 120, 2542] regarded it "The extension of the bleaching signal at longer wavelength indicates the presence of shallow trap state."Overall, the creation of shallow-trap states induced by femtosecond laser and/or transformed from passivation of the deep traps by ambient oxygen are considered to be one of the key factors responsible for the observed enhancement in PL.

Figure S14 .
Figure S14.Pseudo colour TA plots and TA spectra (at delayed 1.5 ps) on untreated MAPbBr3 wafer at different excitation densities.

Figure S15 .
Figure S15.TA spectra at different excitation densities at 1.5 ps of processed MAPbBr3 crystals.