Highly Luminescent and Water Resistant CsPbBr3-CsPb2Br5

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Highly Luminescent and Water Resistant CsPbBr3CsPb2Br5 Perovskite Nanocrystals Coordinated with Partially Hydrolyzed Poly(methyl methacrylate) and Polyethylenimine Guocan Jiang, Chris Guhrenz, Anton Kirch, Luisa Sonntag, Christoph Bauer, Xuelin Fan, Jin Wang, Sebastian Reineke, Nikolai Gaponik, and Alexander Eychmüller ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.9b04179 • Publication Date (Web): 20 Aug 2019 Downloaded from pubs.acs.org on August 20, 2019

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Highly Luminescent and Water Resistant CsPbBr3-CsPb2Br5 Perovskite Nanocrystals Coordinated with Partially Hydrolyzed Poly(methyl methacrylate) and Polyethylenimine Guocan Jiang,† Chris Guhrenz,† Anton Kirch,‡ Luisa Sonntag,† Christoph Bauer,† Xuelin Fan,† Jin Wang,‖ Sebastian Reineke,‡ Nikolai Gaponik†,* and Alexander Eychmüller† †Physical

Chemistry, Technische Universität Dresden, Bergstraße 66b, D-01062 Dresden,

Germany ‡Dresden

Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute

for Applied Physics, Technische Universität Dresden, Nöthnitzer Straße 61, D-01187 Dresden, Germany ‖Key

Laboratory of the Ministry of Education for Advanced Catalysis Materials, Zhejiang

Normal University Jinhua, 321004 Zhejiang, China *corresponding

author: [email protected]

Tel.: +49(0)351 - 463 35203

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ABSTRACT All inorganic lead halide perovskite nanocrystals (PNCs) typically suffer from poor stability against moisture and UV radiation, as well as degradation during thermal treatment. The stability of PNCs can be significantly enhanced through polymer encapsulation, often accompanied by a decrease of photoluminescence quantum yield (PLQY) due to the loss of highly dynamic oleylamine/oleic acid (OLA/OA) ligands. Herein, we propose a solution for this problem by utilizing partially hydrolyzed poly(methyl methacrylate) (h-PMMA) and highly branched poly(ethylenimine) (b-PEI) as double ligands stabilizing the PNCs already during the mechanochemical synthesis (grinding). The hydrophobic polymer of h-PMMA imparts excellent film-forming properties and water stability to the resulting NC–polymer composite. In its own turn, the b-PEI forms an amino-rich, strongly binding ligand layer on the surface of the PNCs being responsible for the significant improvement of the PLQY and the stability of the resulting material. Moreover, the introduction of b-PEI promotes a partial phase conversion from CsPbBr3 to CsPb2Br5 to obtain CsPbBr3/CsPb2Br5 nanocrystals with a core-shell-like structure. As-prepared PNCs solutions are directly processable as inks, while their PLQY drops only slightly from 75% in colloidal solution to 65% in films. Moreover, the final PNC–polymer film exhibits excellent stability against water, heat, and ultraviolet light irradiation. These superior properties allowed us to fabricate a proof of concept thin film OLED with h-PMMA/b-PEI-stabilized PNCs as easily processable, narrowly emitting color conversion composite material. KEYWORDS: CsPbBr3-CsPb2Br5, partially hydrolyzed PMMA, highly branched PEI, high photoluminescence quantum yield, stability

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Due to excellent photophysical properties, such as adjustable band gaps, high molar extinction coefficients, and excellent charge–transfer performance, all-inorganic cesium lead halide perovskite nanomaterials CsPbX3 (X = Cl, Br, or I) have been perfect candidates for many optoelectronic applications, such as solar cells,1 LEDs,2,3 lasers,4 photodetectors,5 field effect transistors (FETs),6 and X-ray scintillators.7 However, moisture, heat, and oxygen make perovskite nanomaterials suffering from poor stability.8,9 For example, they dissolve in polar solvents, such as water, due to the ionic nature of the material itself. Additionally, perovskite nanomaterials easily undergo phase transitions and decompose at high temperature or under UV irradiation. Consequently, recent studies for the improvement of the stability of this material class follow three main routes: (i) introducing an epitaxial shell to form core-shell structures, e.g. CsPbBr3@Cs4PbBr6,10 CsPbBr3@Rb4PbBr6,11 CsPbBr3@PbBr2;12 (ii) modifying the surface, e.g., with additional ligands or inorganic molecules;13-16 and (iii) encapsulating the active material with an inorganic oxide, e.g., SiO2,17-19 AlOx,18 silsesquioxane,20 TiO2,21 ZrO2,22 or hydrophobic polymer matrices, e.g., polystyrene (PS),23,24 PMMA,24-26 Polyvinylidene fluoride (PVDF),27 poly(maleic anhydride-alt-1-octadecene) (PMAO).28 Due to the ionic nature of perovskite materials and the possibility of fast anion exchange, the reported epitaxial shells were typically limited to the above mentioned Cs4PbBr6, Rb4PbBr6, and PbBr2. These wide bandgap semiconductor shells can simultaneously coat the CsPbBr3 core and passivate defects on its surface, thus improving the stability as well as luminescence properties. Oleylamine/oleic acid (OLA/OA) ligands are known to be highly dynamic, i.e. they bind to the PNCs surface with relatively weak forces and are easy to loose during post-preparative treatment or long-time storage.29,30 In order to improve the surface passivation, OLA/OA-capped PNCs can be additionally modified by stronger binding ligands, such as zwitterionic molecules,15 trioctylphosphine (TOP),14 2,2’-iminodibenzoic acid (IDA),16 or bis-(2,2,4- trimethylpentyl)phosphinic acid (TMPPA).13 Such kind of mixed passivation results in PLQY values reaching 90% and an excellent stability of CsPbX3 (X = Br or I) colloids.14-16 Generally, the encapsulation of PNCs provides an effective physical separation from PL quenching molecules and, subsequently, significantly improves the stability of the emissive nanomaterial. HUANG et al.20 applied a cage-like polyhedral oligomeric silsesquioxane (POSS) for the embedding of CsPbX3 (X = Br or I) PNCs. This resulted in the preservation of the PL properties and high stability of the composite even when kept in water. In contrast to inorganic oxides, the encapsulation using hydrophobic polymers carries the advantages of solution processability, flexibility and a variety of opportunities for chemical functionalization. For example, SUN et al.24 applied 4-vinylbenzyl-dimethyloctadecylammonium chloride as surface capping ligand of MAPbBr3 PNCs, followed by an embedding into PS and PMMA copolymers 3


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by a radical-initiated copolymerization between the introduced ligand and MMA, resulting in enhanced stability of the PNCs composite material. However, the above mentioned encapsulated PNCs (both using oxide18-22 or polymer23-28 ) were capped by highly dynamic, easily detachable OLA/OA ligands, resulting in a decrease of the PLQY after encapsulation and long-term storage,31 which is unfavorable for the applications of PNCs as luminophores. Therefore, it remains challenging to maintain a high PLQY while at the same time significantly improving the stability. Herein, we propose a solution for this problem by utilizing a specially designed double ligand system based on partially hydrolyzed PMMA (h-PMMA) and highly branched PEI (b-PEI). Due to its optical clarity and excellent water resistance, PMMA is widely used to encapsulate various nanomaterials or molecular devices,32-35 which prompted us to develop an efficient surface capping ligand based on this polymer. In its own turn, the b-PEI as multidentate ligand provides additional passivation by forming a layer with a strong affinity to the PNC surface.36,37 In contrast to the easily detachable OLA/OA capping,29,30 the b-PEI molecules are not soluble in toluene and remain strongly attached to the PNC surface in colloidal toluene solution. Consequently, it leads to a higher stability and stronger PL of the resulting PNC colloids. Moreover, we observed and describe a phase transition caused by applying h-PMMA and b-PEI as a dual ligand in a ball milling process, which results in the formation of CsPbBr3/CsPb2Br5 nanocrystals with core-shell-like structure. The as-synthesized colloidal solutions of h-PMMA/b-PEI-capped PNCs are directly processable as inks and exhibit excellent photoluminescence. Their PLQY drops only slightly from the original 75% in colloidal solution to 65% in films. More importantly, the PNC–polymer composite possesses superior long-term storage and thermal stability, as well as stability against UV irradiation as compared to OLA/OA capped PNCs encapsulated in PMMA by a conventional blending, making them attractive for solution processable optoelectronic applications, e.g. acting as color conversion layers in combination with an OLED used as pump light source. Our work provides a direct and facile preparation method of polymer-stabilized h-PMMA/b-PEI PNCs and highlights the influence of the ligand chemistry on their PL properties and crystal structure.

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RESULTS AND DISCUSSION Mechanical grinding is a classical top-down approach and can be considered as a simple, effective, and economical method for preparing perovskite nanomaterials.38-41 Herein, we modified a literature known procedure of ZHU et al.39 (for further details see Experimental Section) for the facile synthesis of double polymer ligand h-PMMA/b-PEI-stabilized PNCs. Typically, mixtures of equivalent amounts of the pure metal salts of PbBr2 and CsBr are ground by ball milling. Next, the polymers of h-PMMA and b-PEI dissolved in DCM are added. This leads to a color change of the applied solution after additional grinding, indicating the formation of PNCs. After centrifugation, the resulting solution appears greenish under ambient conditions (Figure 1).

Figure 1. Scheme of the PNC preparation applying ball milling of the solid precursors in the presence of the stabilizing polymers, namely h-PMMA and b-PEI, in DCM.

Spectral Characterization. Our experimental results (Supporting Information (SI), Figure S2) reveal that, following the above-described procedure, pure PMMA is not able to act as a single ligand for stabilizing CsPbBr3 PNCs due to the weak coordination ability of the ester bonds (SI, Figure S2d). Consequently, we partially hydrolyzed PMMA (h-PMMA) by 6, 8, and 10% (for further details see Experimental Section; SI, Figure S2) to form carboxylic acid groups along the polymer chain. This drastically enhances the coordination ability and, finally, stabilizes the perovskite phase. In order to maintain the water resistance of the resulting h-PMMA, the degree of hydrolysis was controlled to be below 10% which was determined by comparing the peak intensities (integral area) of the -OCH3 group before and after LiOH treatment (for further details see Experimental Section) via 1H nuclear magnetic resonance (NMR) spectroscopy (SI, Figure S1) according to reference.42 Applying as prepared h-PMMA (with different degrees of hydrolysis; SI, Figure S2) as a single ligand in our mechanosynthesis 5


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process results in the formation of CsPbBr3 PNCs showing similar photophysical characteristics as summarized in the SI, Table S1. Their first absorption peak maximum (511 nm) and PL maximum (520 nm), as well as their small Stokes shift (9 nm) and narrow full width at half-maximum (FWHM) (19 nm) are comparable with the samples obtained via standard hot injection procedures.3 Differences in the absorbance (SI, Figure S2a) imply an increase in the PNC concentration with increasing degree of PMMA hydrolysis. Nevertheless, as prepared h-PMMA-stabilized PNCs exhibit PLQYs below 10% when dispersed in DCM and of 15–17% when dispersed in toluene, which typically results from the large number of surface dangling bonds associated with under-coordinated surface lead atoms. These low PLQYs are obviously not favorable for applications in LEDs. However, it is known from the hot injection synthesis,34 that the interplay of surface ligands having both carboxylic and amine functional groups can result in strongly fluorescing PNCs. Moreover, it was shown that a surface treatment of a purified CsPbBr3 PNC solution with OLA can increase the PLQY from 40% to 83%, probably due to a higher fraction of tightly bound OLA molecules.30 Additionally, the post-synthetic passivation of defects in MAPbBr3 films through the coordination of nitrogen atoms with under-coordinated lead atoms proved to enhance both the optical properties and the device stability.37 Therefore, we introduced a molecule with a large number of amino groups, namely b-PEI, as a second ligand for the surface modification of the PNCs. We abstain from the further (post-preparative) treatment of the PNCs in the chlorinated solvent DCM and used toluene for the dilution of the dual ligand-stabilized perovskite colloids after grinding, since the insolubility of b-PEI in toluene43 may promote the interaction of the amine groups with lead and bromide ions and, thus, additionally compensates unsaturated bonds on the PNC surface. As a result, the PLQYs of the h-PMMA/b-PEI-capped PNCs increased from around 35% in DCM up to above 50% in toluene. Furthermore, we investigated the optimum amount of b-PEI to be added as a co-ligand to h-PMMA with a hydrolysis degree of 10%. As can be seen from Figure 2a, the use of relatively small amounts (i.e., 0.01 g and 0.02 g, exact compositions of the reaction mixtures are provided in the Experimental Section) of b-PEI resulted in an enhanced PL of the dual ligand-stabilized PNC colloids without influencing the spectral positions (Figure 2b). Indeed, the PLQY values reached 46% and even 75% when using 0.01 g and 0.02 g of b-PEI (Figure 2c), respectively. However, higher amounts (> 0.03 g) were hindering the formation of PNCs, presumably, due to the interaction and complexation of b-PEI molecules with lead bromide on the perovskite surface. Thus, the excessive amine content caused the dissolution of the PNCs (Figure 2a), while a moderate amount of b-PEI could act as an additional surface capping 6


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ligand effectively passivating surface dangling bonds and increasing the PLQY. Generally, the introduction of b-PEI as amine-containing ligand resulted in a small blue shift (~2–3 nm) in the first excitonic transition and PL maximum, as compared to pure h-PMMA-stabilized PNCs, while the small Stokes shift (~7 nm) and narrow FWHM (~18 nm) were preserved (SI, Table S2). Varying the amount of h-PMMA(10%) in the mechanosynthesis (while maintaining the b-PEI content constant) did not influence the PL of the resulting PNCs (SI, Figure S3). Thus, it was found that applying both 0.1 g of h-PMMA(10%) and 0.02 g of b-PEI in our ball milling procedure resulted in the highest PLQY (up to 75%) and an optimal reaction yield. We note, that these PLQYs of polymer-capped PNCs prepared via mechanical grinding reached typical values reported for the classical hot-injection synthesis. Further insights in the PL properties of the single and dual ligand-stabilized PNCs can be obtained from fluorescence lifetime measurements. The prolonged fluorescence lifetime, shown in Figure 2d, is due to the role of PEI surface ligands, which can not only passivate surface traps, but also improve passivation through carboxylic acid groups of the h-PMMA.30 Both mentioned phenomena could suppress non-radiative decay processes in the proper passivated PNCs. We note, that this behavior is expected for the case when both radiative and non-radiative processes share the same excited state.44 It is even more important to note that the PLQYs of h-PMMA/b-PEI-stabilized PNCs decreased only slightly, e.g., from 75% to 65%, when the colloidal solution was dried to form a polymer film (Figure 2c). In fact, this way of preparing polymer films was more advantageous than blending OLA/OA-capped PNCs with PMMA, as introduced by PROTESESCU et al.,45 which resulted in PLQYs of below 15%. We suggest, that a dynamic equilibrium of the surface ligands, like that observed for OLA/OA-capped PNCs in solution,30 is strongly reduced during the blending. Consequently, applying our approach, PMMA has not to be introduced as a ligand/surrounding disturbing the existing ligand shell. This results in a sufficiently higher PLQY of the PNC–polymer film. Additionally, the insolubility of the b-PEI molecules in toluene reduces the possibility of desorption of the amine-containing polymer from the PNC surface, which, finally, enhances their interaction and reduces PL quenching.

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Figure 2. a) Images of the PNC solutions with increasing b-PEI content under ambient (top) and UV light excitation (bottom), as well as the corresponding absorbance and PL spectra (b) and PLQY values (c). Frame d) shows the time-resolved PL. The increase in the PLQY is in agreement with the observed lifetime changes. For all samples, 0.1 g of h-PMMA(10%) was used in the mechanosynthesis.

Morphological Characterization. Pure PMMA-stabilized PNCs with an edge length of 30–40 nm and lattice fringes of 0.588 nm are typically cubic-shaped, as can be seen from (high resolution) the transmission electron microscopy (TEM) images in Figure 3a. These PNCs display the characteristic orthogonal crystal structure (Figure 3c). The introduction of b-PEI in the ball milling process results in an irregular shape (Figure 3b) of the PNCs and in a phase transition. Both tetragonal CsPb2Br5 PNCs with a dominant reflex at 29.3° 2θ and minor amounts of CsPbBr3 particles are coexisting in the resulting PNC solution, as can be seen from the diffraction patterns (Figure 3c). This is in agreement with EDS data (Figure S4, Table S4) showing an increase in the Cs:Pb:Br ratio towards a more lead bromide-rich phase (~1:1.7:4.3) in the films prepared from b-PEI/h-PMMA-stabilized PNCs.

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It is known from the literature,46,47 that amine groups are interacting with lead halides. Consequently, the introduction of b-PEI into the ball milling process can support the dissolution of PbBr2 by complexation. Following, the generation of a second phase, namely CsPb2Br5 can be ascribed as: CsPbBr3/h-PMMA (in solution) + PbBr2/PEI (in solid)  CsPbBr3/CsPb2Br5/h-PMMA/PEI (in solution). The availability of a limited amount of lead bromide complexes results in the conversion of the small-size CsPbBr3 particles to CsPb2Br5 particles, while the large-size CsPbBr3 particles can be converted to CsPbBr3/CsPb2Br5 core-shell-like nanostructures. As can be seen in the TEM image (Figure 3b), some of CsPbBr3 nanoparticle cores (with a higher contrast) are encapsulated by CsPb2Br5 shells (with a lower contrast). This is in agreement with the lattice parameters acquired from high-resolution TEM investigations, characterizing the corresponding areas of the image (Figure 3b, inset). Generally, such an interesting ligand-assisted transformation of CsPbBr3 PNCs was already observed by BALAKRISHNAN et al.48 Dodecyl dimethylammonium bromide (DDAB) induced the exfoliation of the cubic-shaped particles into 2D CsPb2Br5 nanosheets with tetragonal crystal structure. Here, the complexation of the quaternary amine group proceeds via the formation of [PbBr3]- complexes indicated by an absorption maximum at 318 nm. This maximum is also seen in our spectra (Figure 2b) which further supports the assumed amine-induced PNC transformation. CsPb2Br5 possesses indirect band-gap of 2.979 eV,49,50 while CsPbBr3 is a direct bandgap material with a bandgap energy of about 2.40 eV.10,11 The core-shell-like CsPbBr3/CsPb2Br5 PNCs features a type-I structure, which is believed to be another important reason for the improved stability, high fluorescence and a longer fluorescence lifetime of the resulting material.51,52

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Figure 3. TEM images of a) pure h-PMMA- and b) double polymer ligand h-PMMA/b-PEI-stabilized PNCs synthesized via ball milling. HRTEM images are shown in the inset. Red and blue circles in frame b) highlight typical core-shell-like PNCs and completely phase-transferred CsPb2Br5 PNCs, respectively. Frame c) shows the corresponding XRD patterns. The blue inverted triangles point to CsPbBr3 and the green prisms - to CsPb2Br5 reflexes.

Surface Chemistry. To identify differences in the PNC surface chemistry, we performed X-ray photoelectron spectroscopy (XPS) measurements and compared pure h-PMMA and mixed h-PMMA/b-PEI perovskite–polymer films. All XPS core level spectra were calibrated using the C 1s peak at 284.8 eV. Next to carbon and oxygen arising from the polymeric organics and surrounding, both full XPS spectra (Figure 4a) identify the presence of cesium, lead, and bromide. However, a clear difference can be observed. The appearance of a peak at 399 eV in the double polymer-based composite can be assigned to N 1s and proves the successful introduction of b-PEI. As shown in Figure 4b and 4c, the introduction of amino groups from b-PEI results in an interaction with lead and bromide surface ions which leads to an obvious shift in the energy core level spectra towards lower binding energies. Changes in both core level spectra indicate the binding of b-PEI via Pb…NH and NH…Br linkage, thereby, resulting in good passivation of the PNC surface dangling bonds. The reason for the decrease in the electron binding energies after introducing the b-PEI can be a rearrangement of the electronic environment of both Pb and Br atoms. Introduction of more ligands (both amino and carboxylate terminated) can be responsible for the lowering of the binding energy (e.g. increasing of relative amount of Pb-carboxylate, Pb…NH, NH…Br etc. bonds as compared to the highly energetic Pb-Br bonds). Similar observations were reported in the literature.53,54 The 10


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creation of the electron-rich environment due to the introduction of b-PEI may be also responsible for the lowering of the binding energy. Quantitative XPS analysis reveals that h-PMMA-capped PNCs show cation-rich composition (Cs:Pb:Br = 1.00:1.21:2.79), while the double polymer ligand–PNC composites show a ratio of Cs:Pb:Br = 1.00:2.05:4.91. It is worth to mention, that the molar ratio of the element for double polymer capped PNCs based on the XPS measurement are slightly different from the a ratio of Cs:Pb:Br = 1:1.7:4.3 obtained from the EDS measurement. This might be related to a higher sensitivity of the XPS analysis to a surface composition and can be considered as an additional indirect evidence of the presence of CsPbBr3/CsPb2Br5 core-shell-like structure in h-PMMA/b-PEI capped PNCs.55,56

Figure 4. Comparison of a) the XPS full spectra and b) and c) of the XPS core level spectra of Pb 4f and Br 3d of PMMA-stabilized CsPbBr3 and h-PMMA/b-PEI-stabilized CsPb2Br5-CsPbBr3 PNCs. Frame d) shows the corresponding FTIR measurements. The dotted lines in (a) are provided to highlight the appearance of N1s signal in the h-PMMA/b-PEI-stabilized PNCs. The green shaded areas in (d) are provided to highlight the spectral features discussed in the text.

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The comparison of the Fourier-transform infrared (FTIR) spectra of single and double ligand-stabilized PNCs shows mostly the different stretching and vibration modes of PMMA (Figure 4d). Due to the small amount of b-PEI acting as a second surface ligand on the PNC surface, just the highlighted regions in the FTIR spectrum indicate the successful introduction of b-PEI with typical peaks from N–H stretching modes.57 In this context, also the thermogravimetric analysis (TGA) of the resulting h-PMMA/b-PEI PNC–polymer film implies the implementation of both polymers (Figure S5c) After the complete decomposition of the organics, the remaining material possesses a solid content of 17% indicating a relative high QD loading of the film.

Figure 5. Homogenous PNC–polymer film under air in a) and UV light excitation (at 365 nm) in b) prepared by drop casting on a glass substrate. Next, it was transferred in water. The pictures in c) under ambient conditions and d) under UV light excitation (at 365 nm) show an example of writing with h-PMMA/b-PEI-capped PNC ink. The picture in e) shows the drop-casted film (the same as in a) and b) kept for as long as one month in petri dish filled with water. The corresponding data in f) proves the long time water resistance of the PNC–polymer composite. The temporal evolution of the thermal

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stability tests (heating-cooling between 120 and 25°C, respectively) of the composite film is shown in g).

Processability and Stability. Since double polymer ligand-stabilized PNCs showed the highest PLQY (~75%) and are facile to fabricate via ball milling, we tested the stability of the resulting mixed CsPb2Br5-CsPbBr3 PNCs in solution (toluene) and in polymer composite films. As can be seen from the SI, Figure S6a, the PL of the PNC colloids was almost unchanged after storing for 60 days under ambient conditions indicating excellent stability. This is accompanied by facile processability. Indeed, the PNC solutions can be used as inks for writing, e.g., on paper (Figure 5c and 5d) or can easily form uniform films by drop casting on a substrate (Figure 5a and 5b) and subsequent solvent evaporation. More importantly, the partial hydrolysis of PMMA by 10% and the addition of b-PEI do not affect the water resistance of the resulting polymer film (Figure 5e). In contrast to h-PMMA-capped PNCs or OLA/OA-capped CsPbBr3 PNCs encapsulated in PMMA, 80% of the PL of the PNC–polymer composite retains when placed for 40 days under water (Figure 5f). The experimental results demonstrate that h-PMMA can be used as a ligand for PNCs to impart superior water barrier properties to the material. This may be due to a tighter packaging of the h-PMMA ligands on the surface of PNCs as compared to the case, when the encapsulation of the PNCs into PMMA is done by post-synthetic blending. Moreover, even the thermal stability is sufficiently increased, which was tested by placing the PNC–polymer film on a hot plate. After six heating/cooling cycles (25°C / 120°C) the PL intensity of h-PMMA/b-PEI-capped PNC film retained 70% of its initial value, while the PL intensity of OLA/OA-capped PNCs encapsulated in PMMA dropped to about 10% of its initial value under the same conditions (Figure 5g). For LED applications, a high UV stability is also of advantage. The h-PMMA/b-PEI-capped PNC-polymer film prepared in this work keeps about 60% of its original PL intensity after being treated under a 2W UV light lamp (dominant wavelength at 365 nm) for as long as 120 hours (Figure S6b), while the PL intensity of OLA/OA-capped PNCs encapsulated in PMMA retained only about 15% of its initial value. These experimental results show that the h-PMMA/b-PEI-capped PNC-polymer film maintain superior fluorescence stability against heat and ultraviolet light irradiation. This should be attributed to a stronger binding of b-PEI to the PNC surface as compared to OLA/OA, making them difficult to lose under thermal treatment or UV-irradiation. Overall, these examples of the outperforming stability of h-PMMA/b-PEI capped PNCs films, as compared to OLA/OA-capped PNCs encapsulated in PMMA and OLA/OA-capped PNCs, originated from the combination of the tight h-PMMA encapsulation, the strong ligand binding of b-PEI on the PNC surface and the protecting shell of CsPb2Br5. Green-LED. Conclusively, PNCs feature excellent optical properties making them 13


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promising candidates for display technology.51,58 In terms of color saturation, spectral tunability and PLQY, they can outperform organic luminescent materials.59-61 However, remaining problems such as low operational lifetime and low external quantum efficiency (EQE) prevent the practical use of electrically driven quantum dot LEDs.62 At the same time, using inorganic nanocrystalline materials as color conversion layers coupled to stable and more mature OLEDs, is an approach allowing the synergetic combination of the most promising properties of both organic and inorganic nanomaterials.63,64 For the demonstration of this concept, we prepared a green-emitting hybrid LED based on a blue OLED backlight and our perovskite material serving as conversion layer, separated by a common substrate glass (Figure 6a and b). To indicate the spectral conversion, only one out of four OLED pixels was covered with the PNC–polymer down conversion film. The emission spectra, light conversion efficiency and EQE are provided in Figure 6 (c and d) and in the SI, Figure S7, respectively. Please note, that the PNC-coated OLED pixel emission is composed of OLED electroluminescence (EL) and PNC PL with about 26% of blue EL, i.e. unconverted photons (see SI for further details). Considering this and relating both EQEs of the original OLED and the PNC-covered pixels, yields a conversion efficiency reaching 45% and is thus found to be lower than the PLQY of the film (Figure 6 d and SI). Since conversion efficiency optimization is always a trade-off between increasing the film thickness for complete backlight absorption and keeping it at a reasonable level to reduce reabsorption, this is not surprising. This application, however, demonstrates the great potential of our dual polymer ligand h-PMMA/b-PEI-stabilized PNCs as stable and processable luminescent materials.

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Figure 6. a) Scheme of the configuration of the OLED backlight-based green-emitting QLED and b) picture of the final device under operation. The original blue OLED is shown for comparison. Frame c) provides their emission spectra. Frame d) specifies the contributions of the PNC-pixel’s emission: The converted nanoparticle emission is indicated in green and the unabsorbed OLED backlight contribution in blue, respectively. The PNC-film’s conversion efficiency is presented in the inset (see SI for details). It is found to range around 45% (indicated as vertical line) and is thus lower than the initial PLQY of the pure composite film, which is suspected to be due to reabsorption in the thick film.

CONCLUSIONS We investigated the use of h-PMMA and b-PEI for the direct mechanosynthesis (via ball milling) of narrowly green-emitting PNCs. The hydrophobic polymer of h-PMMA imparts excellent film-forming properties and water stability to the nanocrystals. The highly branched PEI forms an amine-rich, strongly binding ligand layer on the surface of PNCs and additionally, promotes

a

partial

phase

transition

from

CsPbBr3

to

CsPb2Br5.

The

resulting

CsPbBr3/CsPb2Br5 core-shell-like nanocrystals possess significantly increased stability and PLQYs. The resulting PNC solutions emit green light peaked at 517 nm, exhibit small Stokes shifts (7 nm) and narrow FWHMs (18 nm), while maintaining PLQYs of 75%. The films obtained 15


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from the colloidal PNC inks reached PLQYs of 65%, thus retaining 85% of the initial PLQY, which is beneficial for solution processable optoelectronics. Consequently, the applicability of the resulting PNC–polymer film as a green color converter was demonstrated in combination with a blue emitting OLED used as thin-film, large area pump source. EXPERIMENTAL SECTION Chemicals. Cesium bromide (99%, Sigma, CsBr), lead bromide (99%, Sigma, PbBr2), poly(methyl acrylate) (99%, average MW ~ 120.000, Sigma, PMMA), poly(ethylenimine) (99%, MW ~ 800, Sigma, b-PEI), lithium hydroxide (99%, Sigma, LiOH). The chemicals were used directly without further purification. All solvents used for this experiments (DCM, toluene, THF) were of analytical grade. Preparation of Partially Hydrolysed PMMA (h-PMMA). The hydrolysis of PMMA was based with minor modifications on the previously reported method of MANOKRUANG et al.42 Typically, 0.2 g of PMMA-120K was dissolved in 5 mL of THF, followed by the addition of LiOH solution (1 M in deionized water). To reach hydrolysis degrees of 6, 8, and 10%, 0.2 mL, 0.6 mL, and 1 mL of aqueous LiOH were used, respectively. The resulting mixture was stirred for 20 h at 60°C. Next, 100 µL of a 1 M HCl was used for acidification of the reaction product. The addition of 40 mL of deionized water resulted in the precipitation of the h-PMMA. To collect the precipitate, the suspension was centrifuged at 5000 rpm for 5 min and the solid product was washed twice with deionized water. Finally, the h-PMMA was dried in vacuum at 60°C for 12 h. The degree of hydrolysis was determined by 1H-NMR spectroscopy. Preparation of PNCs. The PNC synthesis was based on the work of ZHU et al.39 Generally, PbBr2 (73.4 mg, 0.2 mmol) and CsBr (42.4 mg, 0.2 mmol) were loaded under ambient atmosphere into a zirconia bowl (10 mL) with about 120 zirconia balls (diameter of 2 mm) and mixed by a vibratory mill MM 400 (Retsch). The first grinding process of the educts lasted 30 min at a frequency of 30 Hz. Next, 0.1 g of h-PMMA and 0.02 g of PEI were dissolved in 1 mL of DCM and added to the zirconia bowl. Following, the milling process was continued for another 30 min resulting in the formation of PNCs. Next, the mixture was diluted with 9 mL of toluene and centrifuged for 5 min at 5000 rpm (5500 RCF). The PNC-containing supernatant was used for further characterization and processing. To obtain highly emitting colloidal PNCs with the highest PLQYs, the PNC solution was allowed to stay for a few days resulting in the evaporation of most of the DCM by natural volatilization. OA/OLA-capped CsPbBr3 QDs were synthesized by standard hot injection method following simple blending with PMMA for stability test.3,45 Fabrication and Measurement of a Green-LED. The organic, blue-emitting OLED was 16


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prepared as standard bottom-emitting p-i-n stack comprising the sky-blue fluorophore TBPe.65 The green luminescent layer was formed by drop casting several films of PNC solution on the OLED’s glass substrate without using any further matrix. The corresponding external quantum efficiency (EQE) and PL spectrum of the final device were obtained in an integrating sphere (LMS-100, Labsphere Inc.) equipped with a calibrated spectrometer (CDS-600, Labsphere Inc.). The light conversion efficiency was calculated by comparing the luminous flux of the device at different current densities before and after the introduction of the perovskite composite material. The residual blue backlight in the PL-pixel emission was taken into account (see SI). Characterization Methods. UV/vis and PL spectra were recorded using a Cary 60 spectrophotometer (Varian) and a Fluoromax-4 spectrofluorometer (Horiba Jobin Yvon), respectively. Absolute PL QY measurements were performed using a FluoroLog-3 spectrofluorometer (Horiba Jobin Yvon) equipped with a Quanta-φ integrating sphere at an excitation wavelength of 450 nm. The average PLQY and standard deviation were received from five samples. QDs in solution were investigated in 10 x 10 mm quartz cuvettes, while QD-films were placed inside a Spectralon®-holder mounted at the bottom of the integrating sphere setup. Pure solvents and PMMA films were used for blank measurements. 1H Nuclear magnetic resonance (1H NMR) spectra were measured using an Avance 300 (Bruker) NMR spectrometer.

Time-resolved

PL

decays

were

measured

using

a

FluoroLog-3

spectrofluorometer (Horiba Jobin Yvon) with a pulsed laser diode (410 nm) and a TCSPC module. The average PL lifetimes were calculated at the time, where the initial signal intensity was reduced to 10000/e counts. Fourier-transform infrared (FTIR) spectra were recorded in transmission

mode

on

a

Nicolet

iS5

FTIR

spectrometer

(Thermo

Scientific).

Thermogravimetric analysis (TGA) was performed on a Mettler Toledo TGA/DSC1 STARe System thermal analyzer. Typically, the PNC–polymer films were heated under air from 25 oC to 600 oC with a heating rate of 5 K/min.66 TEM images were obtained from a JEOL JEM-1400 Plus (120 kV) and an FEI Tecnai F30 (300 kV) microscope. High-resolution TEM were measured on a FEI Tecnai F30 microscope equipped with a 300 kV field emission gun. EDS elemental maps and line profiles were acquired on a JEOL JEM-2200FS microscope equipped with a Bruker Quantax 400 system equipped with a 200 kV field emission gun. XRD was carried out in reflection mode on a Bruker AXS D2 PHASER diffraction system with Cu Kα irradiation (λ = 0.154 nm). X-ray photoelectron spectroscopy (XPS) was performed on an ESCALAB 250Xi X-ray photoelectron spectrometer equipped with a monochromated Al Kα X-ray source. For XPS measurements, the PNC–polymer film was milled to a powder and used for further characterization. 17


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ASSOCIATED CONTENT Supporting Information Supporting Information is available free of charge via the Internet at http://pubs.acs.org. 1H

NMR results to determine the degree of hydrolysis of h-PMMA (Figure S1). Spectral data

of PNCs obtained in the presence of h-PMMA with different degrees of hydrolysis (Figure S2, Table S1). Spectroscopic characterization of PNCs stabilized by different amounts of the b-PEI (Table S2) and by different amounts of the h-PMMA (Table S3, Figure S3). EDX data of the PNCs (Figure S4) and corresponding elemental ratios (Table S4). Supplemental XPS, FTIR and TGA data (Figure S5). Supplemental stability test data (Figure S6). External quantum efficiencies (EQEs) of the LEDs (Figure S7). Financial Interest Statement The authors declare no competing financial interest. Author Information Corresponding Author: * E-mail: [email protected]

ORCID Jin Wang: 0000-0003-4740-4304 Sebastian Reineke: 0000-0002-4112-6991 Nikolai Gaponik: 0000-0002-8827-2881 Alexander Eychmüller: 0000-0001-9926-6279 ACKNOWLEDGEMENTS G. J. acknowledges the China Scholarship Council (No. 201706740088). This work was partly supported by the EU Horizon 2020 project MiLEDi (project no. 779373). A.K. received funding from the Cusanuswerk foundation. J.W. received funding from the NSFC (No.21701143). X. F. acknowledges the China Scholarship Council (No. 201606340161). We are grateful to V. Lesnyak and R. Du (TU Dresden) for their valuable discussions. We are grateful to S. Goldberg (TU Dresden) for TEM imaging, F. Eichler (TU Dresden) for the introduction to the PLQY measurements, and M. Georgi (TU Dresden) and T. Tang (IAPP) for help with ink writing. Additionally, the authors acknowledge J. Xu (Zhejiang Normal University) for XPS measurements.

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REFERENCES (1) Sutton, R. J.; Eperon, G. E.; Miranda, L.; Parrott, E. S.; Kamino, B. A.; Patel, J. B.; Hörantner, M. T.; Johnston, M. B.; Haghighirad, A. A.; Moore, D. T.; Snaith, H. J. Bandgap-Tunable Cesium Lead Halide Perovskites with High Thermal Stability for Efficient Solar Cells. Adv. Energy Mater. 2016, 6, 1502458. (2) Lin, K.; Xing, J.; Quan, L. N.; de Arquer, F. P. G.; Gong, X.; Lu, J.; Xie, L.; Zhao, W.; Zhang, D.; Yan, C.; Li, W.; Liu, X.; Lu, Y.; Kirman, J.; Sargent, E. H.; Xiong, Q.; Wei, Z. Perovskite Light-Emitting Diodes with External Quantum Efficiency Exceeding 20 Per Cent. Nature 2018, 562, 245-248. (3) Guhrenz, C.; Benad, A.; Ziegler, C.; Haubold, D.; Gaponik, N.; Eychmüller, A. Solid-State Anion Exchange Reactions for Color Tuning of CsPbX3 Perovskite Nanocrystals. Chem. Mater. 2016, 28, 9033-9040. (4) Xu, Y.; Chen, Q.; Zhang, C.; Wang, R.; Wu, H.; Zhang, X.; Xing, G.; Yu, W. W.; Wang, X.; Zhang, Y.; Xiao, M. Two-Photon-Pumped Perovskite Semiconductor Nanocrystal Lasers. J. Am. Chem. Soc. 2016, 138, 3761-3768. (5) Zeng, J.; Li, X.; Wu, Y.; Yang, D.; Sun, Z.; Song, Z.; Wang, H.; Zeng, H. Space-Confined Growth of CsPbBr3 Film Achieving Photodetectors with High Performance in All Figures of Merit. Adv. Funct. Mater. 2018, 28, 1804394. (6) Liu, X.; Kuang, W.; Ni, H.; Tao, Z.; Huang, Q.; Chen, J.; Liu, Q.; Chang, J.; Lei, W. Highly Sensitive and Fast Graphene Nanoribbons/CsPbBr3 Quantum Dots Phototransistor with Enhanced Vertically Metal Oxide Heterostructures. Nanoscale 2018, 10, 10182-10189. (7) Chen, Q.; Wu, J.; Ou, X.; Huang, B.; Almutlaq, J.; Zhumekenov, A. A.; Guan, X.; Han, S.; Liang, L.; Yi, Z.; Li, J.; Xie, X.; Wang, Y.; Li, Y.; Fan, D.; Teh, D. B. L.; All, A. H.; Mohammed, O. F.; Bakr, O. M.; Wu, T.; Bettinelli, M.; Yang, H.; Huang, W.; Liu, X. All-Inorganic Perovskite Nanocrystal Scintillators. Nature 2018, 561, 88-93. (8) Deretzis, I.; Smecca, E.; Mannino, G.; La Magna, A.; Miyasaka, T.; Alberti, A. Stability and Degradation in Hybrid Perovskites: Is the Glass Half-Empty or Half-Full? J. Phys. Chem. Lett. 2018, 9, 3000-3007. (9) Ding, D.; Li, H.; Li, J.; Li, Z.; Yao, H.; Liu, L.; Tian, B. B.; Su, C.; Chen, F.; Shi, Y. Effect of Mechanical Forces on Thermal Stability Reinforcement for Lead Based Perovskite Materials. J. Mater. Chem. A 2019, 7, 540-548. (10) Jia, C.; Li, H.; Meng, X.; Li, H. CsPbX3/Cs4PbX6 Core/Shell Perovskite Nanocrystals. Chem. Commun. 2018, 54, 6300-6303. (11) Wang, B.; Zhang, C.; Huang, S.; Li, Z.; Kong, L.; Jin, L.; Wang, J.; Wu, K.; Li, L. Postsynthesis Phase Transformation for CsPbBr3/Rb4PbBr6 Core/Shell Nanocrystals with Exceptional Photostability. ACS Appl. Mater. Interfaces 2018, 10, 23303-23310. (12) Ruan, L. J.; Tang, B.; Ma, Y. Improving the Stability of CsPbBr3 Nanocrystals in Ethanol by Capping with PbBr2-Adlayers. J. Phys. Chem. C 2019, 123, 11959-11967. (13) Wang, C.; Chesman, A. S.; Jasieniak, J. J. Stabilizing the Cubic Perovskite Phase of CsPbI3 Nanocrystals by Using an Alkyl Phosphinic Acid. Chem. Commun. 2016, 53, 232-235. (14) Liu, F.; Zhang, Y.; Ding, C.; Kobayashi, S.; Izuishi, T.; Nakazawa, N.; Toyoda, T.; Ohta, T.; Hayase, S.; Minemoto, T.; Yoshino, K.; Dai, S.; Shen, Q. Highly Luminescent Phase-Stable CsPbI3 Perovskite Quantum Dots Achieving Near 100% Absolute Photoluminescence Quantum Yield. ACS Nano 2017, 11, 10373-10383. (15) Krieg, F.; Ochsenbein, S. T.; Yakunin, S.; Ten Brinck, S.; Aellen, P.; Suess, A.; Clerc, B.; Guggisberg, D.; Nazarenko, O.; Shynkarenko, Y.; Kumar, S.; Shih, C. J.; Infante, I.; Kovalenko, M. V. Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and Stability. ACS Energy Lett. 2018, 3, 641-646. (16) Pan, J.; Shang, Y. Q.; Yin, J.; De Bastiani, M.; Peng, W.; Dursun, I.; Sinatra, L.; El-Zohry, A. M.; Hedhili, M. N.; Emwas, A. H.; Mohammed, O. F.; Ning, Z. J.; Bakr, O. M. Bidentate Ligand-Passivated CsPbI3 Perovskite Nanocrystals for Stable Near-Unity Photoluminescence Quantum Yield and Efficient Red Light-Emitting Diodes. J. Am. Chem. Soc. 2018, 140, 562-565. (17) Cai, J.; Gu, K.; Zhu, Y.; Zhu, J.; Wang, Y.; Shen, J.; Trinchi, A.; Li, C.; Wei, G. Highly Stable CsPbBr3@SiO2 Nanocomposites Prepared via Confined Condensation for Use as a Luminescent Ink. Chem. Commun. 2018, 54, 8064-8067. (18) Li, Z. C.; Kong, L.; Huang, S. Q.; Li, L. Highly Luminescent and Ultrastable CsPbBr3 Perovskite Quantum Dots Incorporated into a Silica/Alumina Monolith. Angew. Chem. Int. Ed. 2017, 56, 8134-8138. (19) Xu, L.; Chen, J.; Song, J.; Li, J.; Xue, J.; Dong, Y.; Cai, B.; Shan, Q.; Han, B.; Zeng, H. Double-Protected All-Inorganic Perovskite Nanocrystals by Crystalline Matrix and Silica for Triple-Modal Anti-Counterfeiting Codes. ACS Appl. Mater. Interfaces 2017, 9, 26556-26564. (20) Huang, H.; Chen, B.; Wang, Z.; Hung, T. F.; Susha, A. S.; Zhong, H.; Rogach, A. L. Water Resistant CsPbX3 Nanocrystals Coated with Polyhedral Oligomeric Silsesquioxane and their Use as Solid State Luminophores in All-Perovskite White Light-Emitting Devices. Chem. Sci. 2016, 7, 5699-5703. (21) Li, Z.-J.; Hofman, E.; Li, J.; Davis, A. H.; Tung, C.-H.; Wu, L.-Z.; Zheng, W. Photoelectrochemically Active and Environmentally Stable CsPbBr3/TiO2 Core/Shell Nanocrystals. Adv. Funct. Mater. 2018, 28, 1704288. (22) Liu, H.; Tan, Y.; Cao, M.; Hu, H.; Wu, L.; Yu, X.; Wang, L.; Sun, B.; Zhang, Q. Fabricating CsPbX3-Based Type I and Type II Heterostructures by Tuning the Halide Composition of Janus CsPbX3/ZrO2 Nanocrystals. ACS Nano 2019, 13, 5366-5374.

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(23) Raja, S. N.; Bekenstein, Y.; Koc, M. A.; Fischer, S.; Zhang, D.; Lin, L.; Ritchie, R. O.; Yang, P.; Alivisatos, A. P. Encapsulation of Perovskite Nanocrystals into Macroscale Polymer Matrices: Enhanced Stability and Polarization. ACS Appl. Mater. Interfaces 2016, 8, 35523-35533. (24) Sun, H.; Yang, Z.; Wei, M.; Sun, W.; Li, X.; Ye, S.; Zhao, Y.; Tan, H.; Kynaston, E. L.; Schon, T. B.; Yan, H.; Lu, Z. H.; Ozin, G. A.; Sargent, E. H.; Seferos, D. S. Chemically Addressable Perovskite Nanocrystals for Light-Emitting Applications. Adv. Mater. 2017, 29, 1701153. (25) Pan, A.; Wang, J.; Jurow, M. J.; Jia, M.; Liu, Y.; Wu, Y.; Zhang, Y.; He, L.; Liu, Y. General Strategy for the Preparation of Stable Luminous Nanocomposite Inks Using Chemically Addressable CsPbX3 Peroskite Nanocrystals. Chem. Mater. 2018, 30, 2771-2780. (26) Zhang, X.; Wang, H.-C.; Tang, A.-C.; Lin, S.-Y.; Tong, H.-C.; Chen, C.-Y.; Lee, Y.-C.; Tsai, T.-L.; Liu, R.-S. Robust and Stable Narrow-Band Green Emitter: An Option for Advanced Wide-Color-Gamut Backlight Display. Chem. Mater. 2016, 28, 8493-8497. (27) Zhou, Q.; Bai, Z.; Lu, W. G.; Wang, Y.; Zou, B.; Zhong, H. In Situ Fabrication of Halide Perovskite Nanocrystal-Embedded Polymer Composite Films with Enhanced Photoluminescence for Display Backlights. Adv. Mater. 2016, 28, 9163-9168. (28) Wu, H.; Wang, S.; Cao, F.; Zhou, J.; Wu, Q.; Wang, H.; Li, X.; Yin, L.; Yang, X. Ultrastable Inorganic Perovskite Nanocrystals Coated with a Thick Long-Chain Polymer for Efficient White Light-Emitting Diodes. Chem. Mater. 2019, 31, 1936-1940. (29) An, R.; Zhang, F.; Zou, X.; Tang, Y.; Liang, M.; Oshchapovskyy, I.; Liu, Y.; Honarfar, A.; Zhong, Y.; Li, C.; Geng, H.; Chen, J.; Canton, S. E.; Pullerits, T.; Zheng, K. Photostability and Photodegradation Processes in Colloidal CsPbI3 Perovskite Quantum Dots. ACS Appl. Mater. Interfaces 2018, 10, 39222-39227. (30) De Roo, J.; Ibanez, M.; Geiregat, P.; Nedelcu, G.; Walravens, W.; Maes, J.; Martins, J. C.; Van Driessche, I.; Kovalenko, M. V.; Hens, Z. Highly Dynamic Ligand Binding and Light Absorption Coefficient of Cesium Lead Bromide Perovskite Nanocrystals. ACS Nano 2016, 10, 2071-2081. (31) Yoon, H. C.; Lee, S.; Song, J. K.; Yang, H.; Do, Y. R. Efficient and Stable CsPbBr3 Quantum-Dot Powders Passivated and Encapsulated with a Mixed Silicon Nitride and Silicon Oxide Inorganic Polymer Matrix. ACS Appl. Mater. Interfaces 2018, 10, 11756-11767. (32) Zhang, F.; Zhong, H. Z.; Chen, C.; Wu, X. G.; Hu, X. M.; Huang, H. L.; Han, J. B.; Zou, B. S.; Dong, Y. P. Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology. ACS Nano 2015, 9, 4533-4542. (33) Mutlugun, E.; Hernandez-Martinez, P. L.; Eroglu, C.; Coskun, Y.; Erdem, T.; Sharma, V. K.; Unal, E.; Panda, S. K.; Hickey, S. G.; Gaponik, N.; Eychmüller, A.; Demir, H. V. Large-Area (over 50 cm x 50 cm) Freestanding Films of Colloidal InP/ZnS Quantum Dots. Nano Lett. 2012, 12, 3986-3993. (34) Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Lett. 2015, 15, 3692-3696. (35) Bi, D.; Yi, C.; Luo, J.; Décoppet, J.-D.; Zhang, F.; Zakeeruddin, S. M.; Li, X.; Hagfeldt, A.; Grätzel, M. Polymer-Templated Nucleation and Crystal Growth of Perovskite Films for Solar Cells with Efficiency Greater than 21%. Nat. Energy 2016, 1, 16142. (36) Zuo, L. J.; Guo, H. X.; deQuilettes, D. W.; Jariwala, S.; De Marco, N.; Dong, S. Q.; DeBlock, R.; Ginger, D. S.; Dunn, B.; Wang, M. K.; Yang, Y. Polymer-Modified Halide Perovskite Films for Efficient and Stable Planar Heterojunction Solar Cells. Sci. Adv. 2017, 3, 1700106. (37) Lee, S.; Park, J. H.; Lee, B. R.; Jung, E. D.; Yu, J. C.; Di Nuzzo, D.; Friend, R. H.; Song, M. H. Amine-Based Passivating Materials for Enhanced Optical Properties and Performance of Organic-Inorganic Perovskites in Light-Emitting Diodes. J. Phys. Chem. Lett. 2017, 8, 1784-1792. (38) Protesescu, L.; Yakunin, S.; Nazarenko, O.; Dirin, D. N.; Kovalenko, M. V. Low-Cost Synthesis of Highly Luminescent Colloidal Lead Halide Perovskite Nanocrystals by Wet Ball Milling. ACS Appl. Nano Mater. 2018, 1, 1300-1308. (39) Zhu, Z. Y.; Yang, Q. Q.; Gao, L. F.; Zhang, L.; Shi, A. Y.; Sun, C. L.; Wang, Q.; Zhang, H. L. Solvent-Free Mechanosynthesis of Composition-Tunable Cesium Lead Halide Perovskite Quantum Dots. J. Phys. Chem. Lett. 2017, 8, 1610-1614. (40) Jana, A.; Mittal, M.; Singla, A.; Sapra, S. Solvent-Free, Mechanochemical Syntheses of Bulk Trihalide Perovskites and their Nanoparticles. Chem. Commun. 2017, 53, 3046-3049. (41) Huang, H.; Xue, Q.; Chen, B.; Xiong, Y.; Schneider, J.; Zhi, C.; Zhong, H.; Rogach, A. L. Top-Down Fabrication of Stable Methylammonium Lead Halide Perovskite Nanocrystals by Employing a Mixture of Ligands as Coordinating Solvents. Angew. Chem. Int. Ed. 2017, 56, 9571-9576. (42) Manokruang, K.; Manias, E. Hollow Microspheres and Aqueous Phase Behavior of pH-Responsive Poly(methyl methacrylate-co-methacrylic acid) Copolymers with a Blocky Comonomer Distribution. Mater. Lett. 2009, 63, 1144-1147. (43) Nann, T. Phase-Transfer of CdSe@ZnS Quantum Dots Using Amphiphilic Hyperbranched Polyethylenimine. Chem. Commun. 2005, 13, 1735-1736. (44) Pu, C.; Qin, H.; Gao, Y.; Zhou, J.; Wang, P.; Peng, X. Synthetic Control of Exciton Behavior in Colloidal Quantum Dots. J. Am. Chem. Soc. 2017, 139, 3302-3311.

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(45) Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Bertolotti, F.; Masciocchi, N.; Guagliardi, A.; Kovalenko, M. V. Monodisperse Formamidinium Lead Bromide Nanocrystals with Bright and Stable Green Photoluminescence. J. Am. Chem. Soc. 2016, 138, 14202-14205. (46) Grisorio, R.; Di Clemente, M. E.; Fanizza, E.; Allegretta, I.; Altamura, D.; Striccoli, M.; Terzano, R.; Giannini, C.; Irimia-Vladu, M.; Suranna, G. P. Exploring the Surface Chemistry of Cesium Lead Halide Perovskite Nanocrystals. Nanoscale 2018, 11, 986-999. (47) Kerner, R. A.; Schloemer, T. H.; Schulz, P.; Berry, J. J.; Schwartz, J.; Sellinger, A.; Rand, B. P. Amine Additive Reactions Induced by the Soft Lewis Acidity of Pb2+ in Halide Perovskites. Part I: Evidence for Pb–Alkylamide Formation. J. Mater. Chem. C 2019, 7, 5251-5259. (48) Balakrishnan, S. K.; Kamat, P. V. Ligand Assisted Transformation of Cubic CsPbBr3 Nanocrystals into Two-Dimensional CsPb2Br5 Nanosheets. Chem. Mater. 2017, 30, 74-78. (49) Li, G. P.; Wang, H.; Zhu, Z. F.; Chang, Y. J.; Zhang, T.; Song, Z. H.; Jiang, Y. Shape and Phase Evolution from CsPbBr3 Perovskite Nanocubes to Tetragonal CsPb2Br5 Nanosheets with an Indirect Bandgap. Chem. Commun. 2016, 52, 11296-11299. (50) Iyikanat, F.; Sari, E.; Sahin, H. Thinning CsPb2Br5 Perovskite Down to Monolayers: Cs-Dependent Stability. Phys. Rev. B 2017, 96, 155442. (51) Zhang, X.; Xu, B.; Zhang, J.; Gao, Y.; Zheng, Y.; Wang, K.; Sun, X. W. All-Inorganic Perovskite Nanocrystals for High-Efficiency Light Emitting Diodes: Dual Phase CsPbBr3-CsPb2Br5 Composites. Adv. Funct. Mater. 2016, 26, 4595-4600. (52) Qiao, B.; Song, P.; Cao, J.; Zhao, S.; Shen, Z.; Di, G.; Liang, Z.; Xu, Z.; Song, D.; Xu, X. Water-Resistant, Monodispersed and Stably Luminescent CsPbBr3/CsPb2Br5 Core-Shell-Like Structure Lead Halide Perovskite Nanocrystals. Nanotechnology 2017, 28, 445602. (53) Li, M.; Zhang, X.; Matras-Postolek, K.; Chen, H. S.; Yang, P. An Anion-Driven Sn2+ Exchange Reaction in CsPbBr3 Nanocrystals towards Tunable and High Photoluminescence. J. Mater. Chem. C 2018, 6, 5506-5513. (54) Woo, J. Y.; Kim, Y.; Bae, J.; Kim, T. G.; Kim, J. W.; Lee, D. C.; Jeong, S. Highly Stable Cesium Lead Halide Perovskite Nanocrystals through in Situ Lead Halide Inorganic Passivation. Chem. Mater. 2017, 29, 7088-7092. (55) Papagiannouli, I.; Patanen, M.; Blanchet, V.; Bozek, J. D.; de Anda Villa, M.; Huttula, M.; Kokkonen, E.; Lamour, E.; Mevel, E.; Pelimanni, E.; Scalabre, A.; Trassinelli, M.; Bassani, D. M.; Lévy, A.; Gaudin, J. Depth Profiling of the Chemical Composition of Free-Standing Carbon Dots Using X-ray Photoelectron Spectroscopy. J. Phys. Chem. C 2018, 122, 14889-14897. (56) Lincheneau, C.; Amelia, M.; Oszajca, M.; Boccia, A.; D'Orazi, F.; Madrigale, M.; Zanoni, R.; Mazzaro, R.; Ortolani, L.; Morandi, V.; Silvi, S.; Szaciłowski, K.; Credi, A. Synthesis and Properties of ZnTe and ZnTe/ZnS Core/Shell Semiconductor Nanocrystals. J. Mater. Chem. C 2014, 2, 2877-2886. (57) Han, T.; Yuan, Y.; Liang, X.; Zhang, Y.; Xiong, C.; Dong, L. Colloidal Stable Quantum Dots Modified by Dual Functional Group Polymers for Inkjet Printing. J. Mater. Chem. C 2017, 5, 4629-4635. (58) Chen, X. M.; Zhang, F.; Ge, Y.; Shi, L. F.; Huang, S.; Tang, J. L.; Lv, Z.; Zhang, L.; Zou, B. S.; Zhong, H. Z. Centimeter-Sized Cs4PbBr6 Crystals with Embedded CsPbBr3 Nanocrystals Showing Superior Photoluminescence: Nonstoichiometry Induced Transformation and Light-Emitting Applications. Adv. Funct. Mater. 2018, 28, 1706567. (59) Murray, C. B.; Norris, D. J.; Bawendi, M. G. Synthesis And Characterization Of Nearly Monodisperse Cde (E = S, Se, Te) Semiconductor Nanocrystallites. J. Am. Chem. Soc. 1993, 115, 8706-8715. (60) Anikeeva, P. O.; Halpert, J. E.; Bawendi, M. G.; Bulovic, V. Quantum Dot Light-Emitting Devices with Electroluminescence Tunable over the Entire Visible Spectrum. Nano Lett. 2009, 9, 2532-2536. (61) Anikeeva, P. O.; Madigan, C. F.; Halpert, J. E.; Bawendi, M. G.; Bulović, V. Electronic and Excitonic Processes in Light-Emitting Devices Based on Organic Materials and Colloidal Quantum Dots. Phys. Rev. B 2008, 78, 085434. (62) Shirasaki, Y.; Supran, G. J.; Bawendi, M. G.; Bulović, V. Emergence of Colloidal Quantum-Dot Light-Emitting Technologies. Nat. Photonics 2013, 7, 13-23. (63) Wood, V.; Bulovic, V. Colloidal Quantum Dot Light-Emitting Devices. Nano Rev. 2010, 1, 5202. (64) Dai, X.; Deng, Y.; Peng, X.; Jin, Y. Quantum-Dot Light-Emitting Diodes for Large-Area Displays: Towards the Dawn of Commercialization. Adv. Mater. 2017, 29, 1607022. (65) Furno, M.; Meerheim, R.; Hofmann, S.; Lüssem, B.; Leo, K. Efficiency and Rate of Spontaneous Emission in Organic Electroluminescent Devices. Phys. Rev. B 2012, 85, 115205. (66) Xiao, L.; Lin, R.; Wang, J.; Cui, C.; Wang, J.; Li, Z. A Novel Hollow-Hierarchical Structured Bi2WO6 with Enhanced Photocatalytic Activity for CO2 Photoreduction. J. Colloid Interface Sci. 2018, 523, 151-158.

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Table of Contents (TOC) Highly Luminescent and Water Resistant CsPbBr3-CsPb2Br5 Perovskite Nanocrystals Coordinated with Partially Hydrolyzed Poly(methyl methacrylate) and Polyethylenimine Guocan Jiang, Chris Guhrenz, Anton Kirch, Luisa Sonntag, Christoph Bauer, Xuelin Fan, Jin Wang, Sebastian Reineke, Nikolai Gaponik*, and Alexander Eychmülle

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Highly Luminescent and Water Resistant CsPbBr3-CsPb2Br5

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