Suppression of Trion Formation in CsPbBr3 Perovskite Nanocrystals

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C: Physical Processes in Nanomaterials and Nanostructures 3

Suppression of Trion Formation in CsPbBr Perovskite Nanocrystals by Postsynthetic Surface Modification Satoshi Nakahara, Hirokazu Tahara, Go Yumoto, Tokuhisa Kawawaki, Masaki Saruyama, Ryota Sato, Toshiharu Teranishi, and Yoshihiko Kanemitsu J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 27 Aug 2018 Downloaded from http://pubs.acs.org on August 27, 2018

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The Journal of Physical Chemistry

Suppression of Trion Formation in CsPbBr3 Perovskite Nanocrystals by Postsynthetic Surface Modification Satoshi Nakahara, Hirokazu Tahara, Go Yumoto, Tokuhisa Kawawaki, Masaki Saruyama, Ryota Sato, Toshiharu Teranishi, and Yoshihiko Kanemitsu* Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan AUTHOR INFORMATION Corresponding Author *E-mail: [email protected].

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ABSTRACT Lead halide perovskite nanocrystals (NCs) are one of the most anticipated and promising materials for light emitting diodes and lasers because of their high photoluminescence quantum yields (PLQYs). However, the formation of trions (charged excitons) in the NCs reduces their PLQYs. Here, we clarify the trion formation mechanism in perovskite CsPbBr3 NCs by analyzing the excitation fluence dependence of transient absorption signals. Under weak photoexcitation, trions are formed by charge carrier trapping at surface states. In contrast, biexciton Auger recombination dominates the trion formation under strong photoexcitation. We found that the postsynthetic surface treatment suppresses the extrinsic surface-related formation of trions. The thorough understanding of the trion formation mechanisms is essential for the PLQY improvement of perovskite NCs and helps to reduce ionization of NCs in solid state devices.


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INTRODUCTION Lead halide perovskite semiconductors have been attracting much attention for use in solidstate devices since the pioneering reports of the solid-state solar cells based on perovskite CH3NH3PbI3 thin films in 2012.1,2 In spite of the cost-effective fabrication method, they provide excellent optoelectronic properties such as large absorption coefficients in the visible spectral region, long carrier diffusion lengths, and high photoluminescence quantum yields (PLQYs) even at room temperature.3–6 These properties allow their implementation in high-performance devices such as solar cells,7 light emitting diodes (LEDs),8,9 lasers,10 and photo-modulators.11 Especially the nanocrystals (NCs) of lead halide perovskites are recently being recognized as new candidates for luminescence materials.12–19 According to the literature, it is evident that lead halide perovskite NCs possess superior luminescent optoelectronic properties such as roomtemperature PLQYs of up to 90% at corresponding wavelengths13 and emission wavelengths that are tunable through the size control and the exchange of the halide anion.20,21 However, the luminescence efficiencies of perovskite NCs in the blue and red spectral regions are low compared to that in the green range. Furthermore, the long-term stability of luminescence is also not sufficient for practical device applications. To enable higher efficiencies and stability of luminescence over a wide spectral range, the details of the carrier dynamics that are related to nonradiative recombination processes in the perovskite NCs have to be clarified. In many nanomaterials such as II–VI compound semiconductor NCs and carbon nanotubes, it is well known that trions (charged excitons) determine their optical properties and the device performance of LEDs via nonradiative Auger processes.22–26 Even in perovskite NCs, the results obtained by single dot spectroscopy suggest that the existence of trions has a large impact on the PLQY and recombination processes.27,28 In


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addition, the luminescence enhancement by surface treatments29–31 and the LED efficiency improvement due to Sn doping,32 indicate the existence of extrinsic nonradiative recombination centers in perovskite NCs. It is usually considered that both nonradiative Auger ionization and surface charged traps/defects can contribute to the trion generation in NCs, which results in a PLQY reduction.33–35 However, compared to the case of the colloidal II–VI compound NCs, the understanding of the trion generation processes in the perovskite NCs is still unclear. In this paper, we investigated the trion generation mechanism in CsPbBr3 NCs by employing postsynthetic surface treatments. From analysis of the transient absorption (TA) data with photon statistics, we determined the ratio between the trion and exciton occurrences. The existence of charged NCs was evidenced with the excitation fluence dependence and the comparison of the untreated and surface-treated NCs. We found that trion generation under weak photoexcitation is strongly influenced by the photocharging of NCs via the carrier trapping at the surface states, while nonradiative Auger recombination dominates the trion generation under strong photoexcitation. Furthermore, we clarified that the postsynthetic thiocyanate surface treatment enables a significant reduction of the NC’s photocharging.

RESULTS AND DISCUSSION The samples used in this work were CsPbBr3 NCs, whose steady-state absorption spectrum is shown in Figure 1a. We determined an exciton peak energy of ∼508 nm from the second-order derivative of the absorption spectrum. The insets in Figure 1a are the transmission electron microscope (TEM) image and the NC size distribution derived from the TEM image. The average NC size was 7.6 ± 1.4 nm. Figure 1b shows the TA spectroscopy data obtained from the colloidal solution of these NCs dispersed in octane without stirring (static condition). We used a


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pump pulse with a center wavelength of 440 nm and a white-light probe pulse (details are given in the Supporting Information). Here, the excitation photon fluence was 1.7 10 photons/cm2 per pulse. A strong bleaching signal was observed around 508 nm (2.44 eV), which corresponds to the exciton peak energy. This bleaching signal shows the occupation of the band-edge states by the photoexcited carriers. In addition to the strong photobleaching, a photoinduced absorption signal was observed around 525 nm at early delay times in the sub-picosecond regime. This photoinduced absorption signal is a result of the biexciton Stark shift which occurs upon biexciton formation.36,37 These signals indicate that the photoexcited carrier dynamics are determined not only by excitons but also by exciton complexes such as biexcitons.

Figure 1. (a) Absorption spectrum of the untreated CsPbBr3 NCs. Inset: TEM image and size distribution of the sample. (b) Two-dimensional map of the TA signal from the untreated sample under strong excitation condition (〈 〉 3.0).

To clarify the lifetimes and relative contributions of excitons and exciton complexes, we investigated the excitation fluence dependence of the TA dynamics. In this experiment we changed the excitation photon fluence between 2.6 10 and 1.7 10 photons/cm2, which is sufficient to verify the physics ranging from the weak to the strong excitation regimes. Figure 2a plots the temporal evolution of the differential transmittance under the static condition. The


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temporal changes of the TA signals shown here were obtained by integrating the signal between 497 and 516 nm, which corresponds to the region of the TA signal as shown in Figure 1 (b). The spectrally resolved data are discussed later, but show the same tendency. For low excitation fluences, a single component with a slow lifetime of about 5 ns was observed. This slow lifetime component corresponds to the exciton recombination dynamics. By increasing the excitation fluence a significant contribution from a fast decay appeared in addition to the contribution from the slow component. The fast decay can be expressed by a double-exponential function, which is determined by trions and biexcitons.38–40 Consequently, we performed the fitting of these decay curves with a triple-exponential function () / + ∗ /∗ + / . Here, , ∗ , and are the lifetimes of the exciton, trion, and biexciton components, respectively. A single set of lifetimes was used for all excitation fluences, i.e., we performed a global fitting. The magnitudes , ∗ , and describe the relative generation probabilities of the three components for each excitation fluence. The fitting result is shown in Figure 2a with the dashed curves. Because a single set of lifetimes was sufficient for a good agreement with the experimental results, we concluded that our model is highly plausible and obtained 5.1 ns, ∗ 280 ps, and 52 ps for the exciton, trion, and biexciton lifetimes, respectively, under the static condition.


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Figure 2. Excitation fluence dependence of TA dynamics for untreated NCs under (a) static and (c) stirred condition. The dashed curves are the global fitting results using the triple-exponential function explained in the text. Amplitudes of transient absorption signals from exciton ( ), trion ( ∗ ), and biexciton ( ) components for untreated NCs under (b) static and (d) stirred condition. The solid curves show the fitting results based on the Poisson distribution.

In Figure 2b, the magnitudes of all three components ( , ∗ , ) that were obtained from the fitting are plotted as a function of the photon fluence ". The analysis of their photon-fluence dependence allows us to determine the average number of absorbed photons in each NC. The excitation fluence dependence of the contribution from the exciton can be written as (〈 〉) # (1 $ 〈%〉 ) by using a Poisson distribution for the number of absorbed photons in


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the NCs.39–41 Here, 〈 〉 is the average number of absorbed photons in a NC. 〈 〉 can be defined with 〈 〉 & ∙ " , where & and " represent the average absorption cross section of a NC and the photon fluence, respectively. The above equation for can reproduce the experimental values well (blue curve in Figure 2b), and we were able to determine an average absorption cross section of & 1.8 10 cm2. This absorption cross section is similar to those reported in the previous works.42,43 We also conducted the same experiment and analysis with the same sample under stirring (stirred condition), because it is well known that stirring of the solution significantly reduces the photoinduced charging of NCs.39 Figure 2c shows the TA dynamics that were obtained from the stirred solution by integrating the signal between 497 and 516 nm. The dashed lines in Figure 2c are the global fitting result using the abovementioned triple exponential function. The lifetimes of each component are comparable to those obtained under the static condition. In Figure 2d, the magnitudes of all three components ( , ∗ , ) that were obtained from the fitting are plotted as a function of the photon fluence ". By comparison with Figure 2b, we find that the magnitude of the exciton component is independent of stirring. In contrast, it is clear that the trion generation in our perovskite NCs is suppressed by stirring, as observed in CdSe or PbSe NCs.44,45 However, the trion generation dynamics in neutral and ionized perovskite NCs have not yet been understood completely. For perovskite NCs it has been shown that their PLQY and PL intermittency behaviors are sensitive to the surface condition of the NC.28,29 To understand the influence of the surface trap states on the trion formation, we employed a surface treatment of the NCs with sodium thiocyanate (NaSCN). It has been reported that the NaSCN treatment improves the PLQY of the NCs.29 By using an absolute PLQY spectrometer (Quantaurus-QY, Hamamatsu Photonics) for


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the PLQY measurements, we also confirmed that the PLQY can be improved from 65% to 80% by the surface treatment. To obtain more details about the trion generation, we conducted the TA measurements for the surface-treated NCs under the static and stirred conditions (shown in Figures S2(a)–(d) in the Supporting Information). In the TA signal from the surface-treated NCs under the static condition a bleaching signal with a peak near 507 nm appeared, which is almost the same as that for the untreated NCs. We note that the lifetimes of all three components ( 4.7 ns, ∗ 240 ps, and 46 ps) are almost the same as those of the untreated NCs. This implies that the intrinsic quality was unaffected by the surface treatment, which enables us to discuss the trion formation mechanism in terms of the surface traps. In the same manner as for the untreated NCs, the experimental exciton contributions could be well reproduced with the abovementioned Poisson model for ) (see Figure S2(b), (d); blue lines). Furthermore, we found that the trion component can be observed even after the surface treatment, but in comparison to the exciton signal intensities, the trion contribution became much smaller due to the surface treatment.


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Figure 3. (a) Normalized TA spectra of untreated NCs for an excitation fluence corresponding to 〈 〉 3.0 at five different delay times under the static condition. (b) Time-resolved full width at half-maximum (FWHM) of the bleaching signal observed in the untreated NCs. (c) Decayassociated spectra for untreated NCs and (d) those of the surface-treated NCs.

In the following we discuss the influence of the trion on the temporal evolution of the TA spectra. Figure 3a shows the temporal evolution of the TA spectra obtained from the untreated NCs under the static condition for 〈 〉 3.0. At early delay times, a broadening of the spectra at the low-energy side can be clearly observed. Figure 3b is a plot of the TA spectrum’s full width at half-maximum (FWHM) for different delay times and clarifies that the broadening strongly changes within the first 300 ps, and reaches an almost constant after about 600 ps. This fast relaxation time of the FWHM is in good agreement with the trion lifetime that was estimated


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from the decay dynamics, which suggests that the trion formation contributes to the broadening of the TA spectrum. Therefore, it can be considered that the TA signal of the trion appears at the low energy region below the exciton signal, and this induces the broadening of the TA signal. To investigate the contributions of the exciton, trion and biexciton components on the temporal evolution of the spectra, we evaluated the decay associated spectra (DAS) of the TA signals.46 For this analysis, all decay profiles are fitted with a triple-exponential function for each detected wavelength *: ∆,/,(*, ) ∑.0,∗ , . (*) // . The lifetimes . used here are the same constants that were determined with the abovementioned global fitting procedure. This method allows us to extract the spectral information of each component accurately. The amplitudes . (*) for the untreated and surface-treated NCs are plotted in Figure 3c and 3d, respectively. Here, we measured the TA signals under weak excitation (〈 〉~0.2) and the static condition in order to clearly observe the trion generation. In both samples, the trion component exhibited a peak at lower energies (equivalent to 510 nm) compared to the exciton peak energy (equivalent to 507 nm). The peak position difference between exciton and trion signals corresponds to an energy difference of about 14 meV, and we consider that this reflects the trion binding energy.47,48 The exciton and biexciton components exhibit equivalent spectra for both samples. The trion formation, however, is clearly suppressed at all wavelengths in the treated NCs, and therefore the suppression of the trion formation is also confirmed in the spectrally resolved data.


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Figure 4. Excitation fluence dependence of ratios between trion and exciton amplitude. The red and blue circles represent the results estimated via triple-exponential fitting of the TA data from untreated and surface-treated NCs, respectively. The curves show the fitting results using the Poisson statistics.

To discuss the relative trion generation rate, we plotted the ratio between the trion and exciton amplitudes, ∗ / , as a function of the average number of absorbed photons 〈 〉 in Figure 4. It can be verified that by increasing 〈 〉 , the relative contribution of the trion component becomes larger in both samples. It is evident that under the weak excitation conditions (〈 〉 2 0.2) the trions are generated efficiently in the untreated sample under the static condition, while the generation is almost completely suppressed in the surface-treated sample. To understand this behavior, we consider a model that describes the NC ensemble as a mixture of charged and neutral NCs, which allows us to write the trion contribution as ∗ 3 41 $ 〈%〉 5 + 6 (1 $ 〈%〉 $ 〈 〉 〈%〉 ). Here, the first term expresses the trion generation from the charged NCs due to photocharging. The particular structure inside the brackets means that a trion is formed when one or more photons are absorbed by one NC. The second term expresses the trion generation from the neutral NCs via photoexcitation. This term means that at


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least 2 photons have to be absorbed in a neutral NC to generate a trion. When we use the fact that the exciton component can be written as # (1 $ 〈%〉 ) ,39–41 the ratio between the signal amplitudes of exciton and trion can be expressed as

∗ 1 $ 〈%〉 $ 〈 〉 〈%〉 7+8 1 $ 〈%〉

(1)

Here we use 7 3 /# for a concise notation of the fraction of trions that were generated in the charged NCs, and 8 6 /# defines the fraction of trions that were generated as a result of the multiple photon absorption in neutral NCs. The solid red (blue) curve in Figure 4 is the result obtained from the fitting of the data of the untreated (treated) NCs using eq. 1. We found that our proposed model reproduces the experimental results well. From the fitting result of the untreated NCs under the static condition, we obtained a relatively small but significant value of 7 0.058. This proves that a fraction of the untreated CsPbBr3 NCs was charged under the static condition. Furthermore, the increasing behavior of the trion signal under strong photoexcitation can be explained well with the obtained multiple-photon absorption term 8 1.1. These values, a and b, were reduced by stirring (7 = 0.00 and 8 = 0.87). Such a reduction was also observed when we modified the NCs’ surface. It is highly interesting that we obtained 7 0.00 and 8 0.94 for the surface-treated NCs under the static condition, which means that with the NaSCN treatment almost all charged NCs could be reverted to neutral NCs. The almost complete suppression of the charged NCs indicates that the excess Pb is removed from the NC surface by the NaSCN treatment, hence, the Pb is the origin of the surface trap. Since the photon energy of the pump pulses is quite high compared to the bandgap energy, the photocharging process such as carrier trapping to the NC surface can occur during the relaxation process of hot carriers. Since it was reported that the excess Pb atoms at the NC surface act as electron traps,29 trions generated by


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surface traps are considered to be positively charged. The stirring of the NC solution is also effective for the surface-treated NCs and suppressed the trion generation under both weak and strong excitation regimes (7 = 0.00 and 8 = 0.81). Although the NCs were already surfacetreated, the value of 8 was reduced by stirring. This behavior can be explained by considering another charging pathway: Auger recombination. The nonradiative Auger recombination produces a charge with high excess energy. The surface improvement cannot prevent the ejection of the high-energy carriers (from the NC to the outside of the NC), even though the surface modification is effective to remove the electron traps on the NC surface. Thus, both intrinsic multiphoton absorption processes and extrinsic surface traps are considered to affect to the generation of trions.

CONCLUSION In conclusion, we investigated the influence of the surface treatment on the trion generation dynamics in CsPbBr3 NCs by employing TA measurements. The comparison between surfacetreated and untreated NCs revealed that the surface states of NCs play an important role in the photocharging of NCs. We clarified that trion generation occurred predominantly by charging of surface trap states in the weak photoexcitation regime and by multiple photon absorption in the strong photoexcitation regime. We successfully suppressed the trion generation in the weak photoexcitation regime with the NaSCN treatment. This is the first observation that the trion suppression enhances the PLQY of perovskite NCs. Our investigation of the trion generation and the observation of surface treatment effects that occur even in the static condition provide important information for implementation of perovskite NCs in devices. The findings of the


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present work regarding the trion formation processes in CsPbBr3 NCs and their suppression are important contributions to the fundamental knowledge of this material.

ASSOCIATED CONTENT Supporting Information Sample synthesis, surface treatment with NaSCN, details of TA spectroscopy, TA spectroscopy of SCN-treated NCs. (PDF) AUTHOR INFORMATION Notes The authors declare no competing financial interests. ACKNOWLEDGMENT The authors thank T. Aharen for helpful discussions and experimental help. Part of this work was supported by JST-CREST (JPMJCR16N3).

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Photoluminescence Blinking in Individual Core/Shell CdSe/CdS Nanocrystals. Nano Lett. 2011, 11, 5213–5218. (23) Zhao, J.; Chen, O.; Strasfeld, D. B.; Bawendi, M. G. Biexciton Quantum Yield Heterogeneities in Single CdSe (CdS) Core (Shell) Nanocrystals and Its Correlation to Exciton Blinking. Nano Lett. 2012, 12, 4477–4483. (24) Matsunaga, R.; Matsuda, K.; Kanemitsu, Y. Observation of Charged Excitons in HoleDoped Carbon Nanotubes Using Photoluminescence and Absorption Spectroscopy. Phys. Rev. Lett. 2011, 106, 037404. (25) Klimov, V. I. Multicarrier Interactions in Semiconductor Nanocrystals in Relation to the Phenomena of Auger Recombination and Carrier Multiplication. Annu. Rev. Condens. Matter Phys. 2014, 5, 285–316. (26) Pietryga, J. M.; Park, Y.-S.; Lim, J.; Fidler, A. F.; Bae, W. K.; Brovelli, S.; Klimov, V. I. Spectroscopic and Device Aspects of Nanocrystal Quantum Dots. Chem. Rev. 2016, 116, 10513– 10622. (27) Hu, F.; Yin, C.; Zhang, H.; Sun, C.; Yu, W. W.; Zhang, C.; Wang, X.; Zhang, Y.; Xiao, M. Slow Auger Recombination of Charged Excitons in Nonblinking Perovskite Nanocrystals without Spectral Diffusion. Nano Lett. 2016, 16, 6425–6430. (28) Yarita, N.; Tahara, H.; Saruyama, M.; Kawawaki, T.; Sato, R.; Teranishi, T.; Kanemitsu, Y. Impact of Postsynthetic Surface Modification on Photoluminescence Intermittency in Formamidinium Lead Bromide Perovskite Nanocrystals. J. Phys. Chem. Lett. 2017, 8, 6041– 6047.


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(29) Koscher, B. A.; Swabeck, J. K.; Bronstein, N. D.; Alivisatos, A. P. Essentially Trap-Free CsPbBr3 Colloidal Nanocrystals by Postsynthetic Thiocyanate Surface Treatment. J. Am. Chem. Soc. 2017, 139, 6566–6569. (30) Veldhuis, S. A.; Tay, Y. K. E.; Bruno, A.; Dintakurti, S. S. H.; Bhaumik, S.; Muduli, S. K.; Li, M.; Mathews, N.; Sum, T. C.; Mhaisalkar, S. G. Benzyl Alcohol-Treated CH3NH3PbBr3 Nanocrystals Exhibiting High Luminescence, Stability, and Ultralow Amplified Spontaneous Emission Thresholds. Nano Lett. 2017, 17, 7424–7432. (31) Pan, J.; Shang, Y.; Yin, J.; De Bastiani, M.; Peng, W.; Dursun, I.; Sinatra, L.; El-Zohry, A. M.; Hedhili, M. N.; Emwas, A.-H.; et al. Bidentate Ligand-Passivated CsPbI3 Perovskite Nanocrystals for Stable Near-Unity Photoluminescence Quantum Yield and Efficient Red LightEmitting Diodes. J. Am. Chem. Soc. 2018, 140, 562–565. (32) Wang, H.-C.; Wang, W.; Tang, A.-C.; Tsai, H.-Y.; Bao, Z.; Ihara, T.; Yarita, N.; Tahara, H.; Kanemitsu, Y.; Chen, S.; et al. High-Performance CsPb1−xSnxBr3 Perovskite Quantum Dots for Light-Emitting Diodes. Angew. Chem., Int. Ed. 2017, 129, 13838–13842. (33) Gómez, D. E.; van Embden, J.; Mulvaney, P.; Fernée, M. J.; Rubinsztein-Dunlop, H. Exciton−Trion Transitions in Single CdSe–CdS Core–Shell Nanocrystals. ACS Nano 2009, 3, 2281–2287. (34) Zhao, J.; Nair, G.; Fisher, B. R.; Bawendi, M. G. Challenge to the Charging Model of Semiconductor-Nanocrystal Fluorescence Intermittency from Off-State Quantum Yields and Multiexciton Blinking. Phys. Rev. Lett. 2010, 104, 157403.


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(48) Yin, C.; Chen, L.; Song, N.; Lv, Y.; Hu, F.; Sun, C.; Yu, W. W.; Zhang, C.; Wang, X.; Zhang, Y.; et al. Bright-Exciton Fine-Structure Splittings in Single Perovskite Nanocrystals. Phys. Rev. Lett. 2017, 119, 026401.

TOC GRAPHICS


23

(b) The Journal of Physical3 Chemistry 10

60

2.0

40

20 nm

1.0

0.0 400

20 0

3

6 9 12 15 Length (nm)

Delay Time (ps)

1 2 3 4 5 6 7

Occurrence

Absorbance

80

10

Page 24 of 27 -3

3.0

∆T / T (x 10 )

(a)

80 40 0

2 1

10 10

5

ACS Paragon Plus Environment 0 450

500

550

Wavelength (nm)

600

480

500 520 540 Wavelength (nm)

560

(a) 25 of 27 Page

Static

0 13

6.8 0.39

∆T / T

1 2 10-1 3 4 -2 5 10 6 7 -3 10 8 9 10 (c) 11 12 0 13 10 14 15 10-1 16 17 -2 18 10 19 20 -3 21 10 22 23

j (x 10

10

-2

cm ) 2.9 0.16

1.0

10

∆T / T

10

(b) Chemistry The Journal of Physical -2

10 10

0.0

0.5

1.0

1.5

10

2.0

10

-1

10

∆T / T

∆T / T

1.0

10 10

1

AXX AX* AX

-4

-5

10

12

10

10

-2

10

-1

13

10

14

1.5

2.0

-1

10

0

10

Stirred

-2

-3

AXX AX* AX

-4

-5 ACS Paragon Plus Environment 10

Delay Time (ns)

10

Photon Fluence (cm )

10

-2

j (x 10 cm ) 4.9 2.6 0.39 0.16

1.0

0

-2

Stirred

0.5

10

-3

(d)

0.0

-1

Static

-2

Delay Time (ns)

13

10

10

12

10

13

10

14 -2

Photon Fluence (cm )

1

(b) Chemistry The Journal of Physical 21

Amplitude (normalized)

6.3 ps 50 ps 100 ps 800 ps 1.0 ns

0.5

490

510

530

550

18

1.0

0.0

0.0

0.5

1.0

1.5

2.0

Delay Time (ns)

(d)

Untreated = 0.23 AXX AX* AX

0.5

16

570

Wavelength (nm)

470

19

17

0.0 470

Page 26 of 27

20

FWHM (nm)

1 2 3 4 5 6 7 8 9(c) 10 11 12 13 14 15 16 17 18 19

1.0

Amplitude (normalized)

∆T / T (normalized)

(a)

1.0

Treated = 0.24 AXX AX* AX

0.5

0.0

ACS Paragon Plus Environment 490

510

530

550

Wavelength (nm)

570

470

490

510

530

550

Wavelength (nm)

570

(a) Page 1.0 27 of 27

AX* / AX

1 2 3 4 5 6 7 8

0.6

Untreated Static Stirred

0.8

AX* / AX

0.8

(b) The Journal of Physical 1.0 Chemistry

0.4

0.4 0.2

0.2 0.0 -2 10

0.6

Treated Static Stirred

ACS Paragon Plus Environment 10

-1

10

0

10

1

0.0 -2 10

10

-1

10

0

10

1

Suppression of Trion Formation in CsPbBr3 Perovskite Nanocrystals

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