Efficient Perovskite Light Emitting Diodes - Effect of Composition

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Efficient Perovskite Light Emitting Diodes - Effect of Composition, Morphology and Transport Layers Vittal Prakasam, Francesco Di Giacomo, Robert Abbel, Daniel Tordera, Michele Sessolo, Gerwin H. Gelinck, and Henk J. Bolink ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b15718 • Publication Date (Web): 02 Nov 2018 Downloaded from http://pubs.acs.org on November 2, 2018

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ACS Applied Materials & Interfaces

Efficient Perovskite Light Emitting Diodes - Effect Of Composition, Morphology And Transport Layers Vittal Prakasam †,§, Francesco Di Giacomo ‡, Robert Abbel †, Daniel Tordera †, Michele Sessolo §, Gerwin Gelinck †,#, Henk J. Bolink § * † Holst Centre, High Tech Campus 31, 5656 AE, Eindhoven, The Netherlands ‡ TNO, partner in Solliance, High Tech Campus 21, 5656 AE, Eindhoven, The Netherlands § Instituto de Ciencia Molecular, Universidad de Valencia, C/Catedrático J. Beltrán 2, 46980 Paterna, Spain # Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands

ABSTRACT: Organic-inorganic metal halide perovskites are emerging as novel materials for light-emitting applications due to their high color purity, bandgap tunability, straightforward synthesis and inexpensive precursors. In this work, we improve the performance of 3D perovskite light-emitting diodes (PeLEDs) by tuning the emissive layer composition and thickness and by using small molecule transport layers. Additionally, we correlate PeLED efficiencies to the perovskite structure and morphology. The results show that the PeLEDs containing perovskites with an excess of methylammonium bromide (MABr) to lead bromide (PbBr2) in a 2:1 ratio and a

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layer thickness of 80 nm have the highest performance. The optimized device exhibits a peak luminance of 17,600 cd/m2 and an external quantum efficiency of 3.9 %. Structural and morphological studies reveal a reduction in crystallite size and surface roughness with decreasing perovskite layer thickness and increasing ratio of MABr to PbBr2. Balanced charge injection, spatial charge confinement and the reduction of non-radiative sites can explain the enhanced performance by virtue of favorable morphology and transport layer choice .

KEYWORDS: perovskite, light emitting diode, transport layers, high efficiency, stoichiometric perovskite INTRODUCTION Organic-inorganic metal halide perovskites are attracting great attention as a promising semiconducting material due to their desirable intrinsic optoelectronic properties such as tunable bandgap, strong absorption coefficient, low exciton binding energy, balanced charge mobilities and long diffusion lengths.1–6 They can be described by the general formula ABX3; where A is a monovalent cation, e.g. CH3NH3 + or Cs+; B is a divalent metal, e.g. Pb2+ or Sn2+; and X is a halide anion. The relatively low cost of the precursors and the ability to be solution-processed have made this type of perovskites appealing for large area fabrication.7 Recently, perovskites have been used as active materials in light-emitting devices as they display high color purity with a narrow full width at half minimum (FWHM) of less than 20 nm under electrical excitation.8–16 In its simplest form, a 3D perovskite film (generally referred to as “perovskite”) comprises grains consisting of repeating units of ABX3 unit cells along all directions of a three dimensional Bravais lattice. 3D perovskites are easy to synthesize and have good charge transport properties. By virtue of morphological tuning, interfacial control and the use of different organic or inorganic cations,


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perovskite light-emitting diodes (PeLEDs) with emission colors tuned across the visible spectrum have been reported.17,18 PeLEDs based on 3D perovskites usually suffer from poor performance (in the order of 1 % EQE), although in exceptional cases green PeLEDs with EQEs of 8.5% and 10.4% have been reported, using modified PEDOT:PSS and an inverted device architecture, respectively.9,12 Other strategies to enhance the efficiency include the synthesis of quasi-2D perovskite structures or nanocrystals.19–23,10 Since these strategies involve the addition of large alkylammonium salts or ligands which inevitably dilute the charge transporting species, 3D perovskites remain the most interesting candidates for large-area lighting and display applications. In this report, we use the archetype 3D perovskite, methylammonium lead tribromide (MAPbBr3). We demonstrate that the active layer thickness and the molar ratio of the precursors play a crucial role in the device performance of 3D PeLEDs. In particular, smooth and uniform MAPbBr3 thin films consisting of small crystallites (~55nm) are obtained by using an excess of methylammonium bromide (MABr) in the precursor solution and by reducing the emitting layer thickness to 80 nm. Additionally, we report the use of a small molecule hole transport layer (HTL), Di-NPB

(N4,N4'-(Biphenyl-4,4'-diyl)bis(N4'-(naphthalen-1-yl)-N4,N4'-diphenylbiphenyl-4,4'-

diamine)), for facile solution deposition of perovskite thin films with small crystallites. When the HTL is used in conjunction with an evaporated electron transport layer (ETL), consisting of the small molecular weight compound BmPyPhB (1,3-bis[3,5-di(pyridin-3-yl)phenyl]benzene), charge carriers are confined within the emitting perovskite film. These conditions enable us to reproducibly prepare PeLEDs with peak brightnesses of 17,600 cd/m2, current efficiencies of 16 cd/A and an EQE of 3.9 %. This work highlights the importance of, the emitting layer composition, morphology, thickness and the charge transport layers to achieve optimized PeLEDs. EXPERIMENTAL METHODS AND OPTIMIZATION


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The PeLED device stack used in this work is depicted in Figure 1a. As in most PeLEDs reported to date, PEDOT:PSS (Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is used as the hole injection layer (HIL).16 However, there is a large hole injection barrier due to the energy level mismatch between the PEDOT:PSS work function (~-5.1 eV) and the valence band maximum of wide band gap perovskites of 5.9 eV (Figure 1b).9 Moreover, PEDOT:PSS is also a strong exciton quencher.9 Simple PeLEDs fabricated by us with PEDOT:PSS as HIL, but without any HTL exhibit high leakage currents and poor luminance of less than 100 cd/m2 (Figure S1). One way to improve the luminance is to introduce an HTL. However, it is not trivial to insert an HTL in between the PEDOT:PSS and 3D perovskite layers as i) most hole transporting materials are dissolved by the solvent used to process the perovskite, and ii) these solvents are very polar and therefore lead to poor wetting of the perovskite precursors on the hydrophobic HTL, resulting in poor film quality. Here we introduce Di-NPB as the small molecular weight HTL as it able to withstand the perovskite coating from DMSO (dimethyl sulfoxide) solvent and results in films with uniform morphology. In terms of energy alignment, it is well suited as its highest occupied molecular orbital (HOMO, -5.4 eV) facilitates the injection of holes, whereas the lowest unoccupied molecular orbital (LUMO, -2.4 eV) impedes the transfer of electrons from the perovskite layer to the HTL. However, as most typical hole transporting materials, Di-NPB is a hydrophobic compound that leads to films with a low surface free energy. On this surface, a homogeneous wet layer of the perovskite precursor solution cannot be obtained, unless modified coating techniques are employed.24,25 For this reason, surface treatment of the Di-NPB with a nitrogen plasma was used to increase its surface free energy. As shown in Figure 1c, an untreated Di-NPB film has a contact angle with DMSO of ~37.7˚, which decreases to less than 10˚ (resolution limit) upon 30 s-


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Figure 1. (a) Schematic illustration of the device stack. (b) The energy levels of the various materials, taken from literature.26–28 (c) The contact angles of DMSO on Di-NPB films before and after N2 plasma treatment. (d) Absorption spectra of a 80 nm thick MAPbBr3 film (black line), a 35 nm thick Di-NPB film (red line), and a 80 nm thick MAPbBr3 film coated on top of a 30 nm thick Di-NPB film (green line). (e) Cross-sectional SEM image of a complete PeLED with the EDX elemental scan data. The scale bar represents 250 nm. (f) Photographs of two MAPbBr3 films


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coated on an ITO covered glass substrate containing a structured PEDOT:PSS film (red area) under UV illumination (365 nm); (L) No HTL (R) with Di-NPB between PEDOT:PSS and MAPbBr3.

-of N2 plasma treatment. This creates favorable wetting for the deposition of the perovskite film from DMSO solution without altering the film (Figure S2). To confirm that the Di-NPB film is able to withstand the perovskite deposition process, films of Di-NPB, MAPbBr3 and DiNPB/MAPbBr3 (bilayer) on indium tin oxide (ITO) coated glass substrates were prepared and their UV-vis absorption spectra measured (Figure 1d). The Di-NPB film shows an absorption edge at about 400 nm, in agreement with a band gap of approximately 3 eV.26 The absorption edge of plain MAPbBr3 is in agreement with literature (550 nm)6 and the bilayer film clearly shows the presence of both Di-NPB and MAPbBr3. A cross-sectional scanning electron microscopy (SEM) image of a complete PeLED (Figure 1e) with the corresponding energy dispersive X-ray spectroscopy (EDX) line scan data further confirms the heterojunction architecture. Introducing the Di-NPB eliminates the quenching of the perovskite photoluminescence which occurs when in direct contact with PEDOT:PSS (Figure 1f). The uniform emission is further proof that the Di-NPB remains as a rather consistent layer in between the PEDOT:PSS and the perovskite film. Next, we studied the effect of the emissive layer composition, morphology and thickness. PeLEDs

were

fabricated

with

the

following

structure:

ITO/PEDOT:PSS/Di-

NPB/MAPbBr3/BmPyPhB/LiF/Al (see experimental section for details and Figure 1a,S3). The MAPbBr3 films were spin-coated on top of the HTL as the emissive layer from five different precursor solutions with MABr and PbBr2 in molar ratios of 1:1, 1.5:1, 2:1, 2.5:1 and 3:1. Chlorobenzene was dispensed on top of the perovskite layer while spinning to induce rapid and uniform nucleation, as described elsewhere.29 The thickness of the perovskite films was controlled


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by varying the molar concentrations of the precursor solutions, ranging from 0.8 M, 1 M to 1.53 M. The resulting films had thicknesses of 80 ± 5 nm, 160 ± 10 nm and 350 ± 20 nm, respectively. The films exhibit an absorption band edge at ~550 nm and the green photoluminescence characteristic of MAPbBr3 with a maximum at ~530 nm under UV excitation (Figure S4). The PLQY (photoluminescence quantum yield) of the films increases from 0.5 % to 4 % with increasing MABr:PbBr2 ratio (from 1:1 to 2.5:1) and drops to 3 % for the 3:1 ratio (Figure S5). BmPyPhB is employed as the electron transport molecule, due to its favorable energy levels (HOMO: -6.8 eV; LUMO: -2.6 eV) for blocking holes and injecting electrons, thereby confining charges within the emitting layer.28 The current density-voltage-luminance (JVL) characteristics of the PeLEDs having a 80 nm thick perovskite film at different precursor ratios are shown in Figure 2a and 2b. There are distinct differences for each perovskite composition in the PeLEDs series. The diode rectification is decreasing with increasing MABr:PbBr2 ratios, mainly due to a higher leakage current. PeLEDs made with MABr:PbBr2 ratios of 1:1 and 2.5:1 have low leakage currents and therefore it is possible to observe a clear onset of the current injection around 2.5 V, while this onset is not easily determined for other diodes. The PeLEDs containing the perovskite film with MABr:PbBr2 ratios of 1:1 show electroluminescence starting at around 4 V, but the luminance rapidly levels off and does not exceed 100 cd/m2. However, PeLEDs made with an excess of MABr content in the perovskite layer (1.5:1, 2:1 and 2.5:1) show high luminance in excess of 10,000 cd/m2, decreases to less than 50 cd/m2 for the 3:1 ratio. The origin of this difference in luminance is likely related to the perovskite crystallite size and morphology, as explained later. For the best device, with a 2:1 MABr:PbBr2 ratio, the current density shows ohmic behavior until 3.8 V. Beyond this threshold, the current density rises rapidly and the luminance increases exponentially around 4 V, reaching


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values in excess of 15,000 cd/m2 at a driving voltage of 7 V. The electroluminescence exhibits-

Figure 2. (a) Current-voltage (b) and luminance-voltage characteristics of 80 nm thick PeLEDs made from different molar ratios of the precursors MABr and PbBr2. Inset in (a) is a photograph of the typical light output for a PeLED with an active device area of 16 mm2 at 5V bias. (shown here for 80 nm MAPbBr3 with precursor ratio 2:1). Inset in (b) shows the normalized electroluminescence spectrum of the PeLED. (c) Maximum luminance and (d) maximum current efficiency of the PeLEDs vs. precursor ratios, measured for different perovskite layer thicknesses.


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-emission centered at 530 nm with a narrow FWHM of 20.5 nm in the green region (Figure 2a,2b), with CIE (Commission Internationale de Eclairage) coordinates (0.19, 0.76) (Figure S6). For further stack optimization, we looked at the maximum luminance and maximum current efficiencies obtained from the completed devices with different precursor ratios and MAPbBr3 film thicknesses as shown in Figure 2c and 2d. Each data point represents the average value of two devices from two different batches. The data shows that the PeLEDs containing perovskite films with moderate excess of MABr (1.5:1 and 2:1) show better performance both in terms of luminance and current efficiency. Particularly, in the case of thinner films (80 nm and 160 nm), increasing the MABr:PbBr2 ratio from 1:1 to 2:1 results in an enhancement of at least two orders of magnitude for the peak luminance and the current efficiency, reaching >15,000 cd/m2 and ~14 cd/A. This increase is followed by a gradual drop in performance for the diodes containing perovskites with a higher MABr:PbBr2 ratio of 2.5:1 and 3:1. This suggests that although some excess of MABr can induce positive structural and morphological changes, there is an optimum ratio beyond which undesirable effects take over in a PeLED, as discussed later. Regarding the perovskite film thickness, both peak luminance and current efficiencies increase drastically, as it decreases from 350 ± 20 nm to 160 ± 10 nm to 80 ± 5 nm. In a typical 3D perovskite such as MAPbBr3, high trap state densities and long diffusion lengths lead to high non-radiative recombination rates.30–32 However, a thin layer of perovskite is likely to have less spatial trap state density and more confined charges, than thicker films. This could explain the improved device performance of thinner films irrespective of the precursor ratios. For the best devices (Figure 2a, 2b, S6) the peak luminance and peak current efficiency are 17,600 cd/m2 (7 V) and 16.4 cd/A (6.4 V), respectively. This corresponds to a peak power efficiency of 8.4 lm/W (6 V) and a peak EQE of 3.9 % (6.4 V). These values are among the highest reported for PeLEDs based on 3D perovskites. Further


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attempts at reducing the perovskite film thickness to less than 80 nm were futile, as the resulting films didn’t present uniformity (Figure S7). DISCUSSION

c)

(200)

b)

Max. Current Efficiency (cd/A)

a) (100)

101 100 10-1 10-2 10-3

350  20 nm 160  10 nm 80  5 nm

1:1

d)

Max. Current Efficiency (cd/A)

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1.5:1

2:1

2.5:1

3:1

2.5:1

3:1

MABr : PbBr2

101 100

10-1 10-2 10-3

350  20 nm 160  10 nm 80  5 nm

1:1

1.5:1

2:1

MABr : PbBr2 Figure 3. (a) XRD spectra of the different MAPbBr3 films. Black, Red and Blue lines indicate 80 ± 5 nm, 160 ± 10 nm and 350 ± 20 nm thick films, respectively. (b) FWHM of the (100) XRD peaks at 15° vs. precursor ratios for various thicknesses. (c) SEM images of the 1:1, 1.5:1, 2:1, 2.5:1 and 3:1 MAPbBr3 films (thickness of 80 ± 5 nm). The magnified SEM image of the 2:1 film illustrates that the apparent grains in the enclosed region (the red box) are actually composed of much smaller crystallites. Scale bar in all SEM images represents 200 nm. (d) The mean area


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roughness as a function of precursor ratios for various perovskite thicknesses, obtained from an AFM scan over an area of 30 µm2. To investigate the differences between the various MAPbBr3 films used in the devices, structural and morphological studies were conducted using X-ray diffraction (XRD) and atomic force microscopy (AFM). MAPbBr3 films were prepared on top of PEDOT:PSS/Di-NPB bi-layers to mimic the structure and morphology of the perovskite films in the actual devices. The XRD spectra of all the MAPbBr3 films exhibit main peaks at 14.99˚ and 30.16˚ associated with (100) and (200) planes (Figure 3a), indicating a Pm3m cubic phase.33 In the case of films with excess MABr (2:1, 2.5:1 and 3:1) there are additional peaks at 17.26˚ and 28.19˚ which cannot be assigned to MAPbBr3 or its precursors (incl. complexes with the solvent used, DMSO). These peaks become dominant in the thickest films (i.e. 350 nm ± 20 nm) and are extremely weak in the thinnest films (i.e. 80 ± 5 nm). The presence of these peaks only for non-stoichiometric precursors and for thicker films suggests that this phase is related to the excess of MABr. Furthermore, while an increase in MABr has a negligible effect on the peak positions (Figure S8), the corresponding FWHM increases (Figure 3b), indicating a reduction of the crystallite size. Reducing the thickness from 350 ± 20 nm to 80 ± 5 nm also increases the FWHM of the peaks substantially. Both procedures thus represent simple methods to prepare perovskite thin films with small crystallites. From the line broadening, using the Scherrer equation, we estimate the crystallite size of the best performing perovskite film (with thickness 80 nm and MABr:PbBr2 ratio 2:1) to be ~55 nm. The SEM image in Figure 3c confirms that the 2:1 film is indeed composed of dense crystallites with random orientation, in agreement with the XRD analysis. It has been previously reported that smaller crystallite size is favorable for better spatial charge confinement and increased radiative recombination leading to better PeLEDs9,15, in good agreement with our


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experimental results. These trends convincingly demonstrate that both stoichiometry and thickness can be used to tune the crystallite size in a controlled manner. It has also been suggested that an excess of MABr helps in reducing the formation of quenching Pb atoms within the lattice9, thereby increasing the radiative recombination rate. In contrast, we note that the luminance of the 80 nm thick film with the 3:1 precursor ratio was poor despite the favorable structure and crystallite size. A closer inspection of the film with SEM (Figure 3c), reveals that this film had large pin-holes and an incomplete surface coverage. This suggests that the poor performance of 3:1 films stems from the unfavorable film morphology rather than their internal structure. We also measured the surface roughness of the MAPbBr3 films by AFM (Figure S9). As shown in Figure 3d, there is a gradual increase of the surface roughness with the film thickness increasing, from 80 ± 5 nm to 350 ± 20 nm. With the addition of excess MABr, the 2:1 films tend to form a smooth film with small crystallites, while in the 2.5:1 and 3:1 films the crystallites tend to agglomerate into larger grains, simultaneously creating pinholes and increasing the surface roughness. This corresponds to root-mean-square roughnesses (measured over an area of 30 µm2) of ~3.7 nm and ~10.7 nm (2:1 samples), ~11 nm and ~45 nm (3:1 samples) for 80 ± 5 nm and 350 ± 20 nm thick films, respectively. The different morphologies arise from two phenomena: first, the different coordination of the colloidal particles present in the ink influences the shape of the crystals. Second, the excess of MABr can induce Ostwald ripening to further grow the crystal grain during the annealing stage.34,35 CONCLUSIONS In summary, an excess of MABr can be used in the preparation of MAPbBr3 films with smaller crystallites, which is favorable for the electroluminescence in terms of spatial charge confinement and enhanced bi-molecular radiative recombination. The optimum amount of excess MABr also


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leads to the formation of films with a smooth surface morphology. Another synthetic way to further reduce the crystallite size is to reduce the perovskite layer thickness. This leads to the formation of closely packed smooth films with tiny crystallites. The combination of perovskite films with optimized composition and morphology (MABr:PbBr2 - 2:1; 80 nm) with transport layers having favorable energy levels leads us to demonstrate 3D PeLEDs based on MAPbBr3 with high brightness of 17,600 cd/m2 and EQE of 3.9 %. Our study also shows that charge confinement can be achieved by using Di-NPB and BmPyPhB as small molecule HTL and ETL, respectively. In addition, it paves the way toward facile PeLED production based on simple precursor solutions with the potential to achieve upscaling to large area devices. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS publications website. Materials and Perovskite precursor preparation; Experimental section; Optical and electrical characterization; J-V-L of devices without HTL; Molecular structures; Device efficiencies and AFM scan. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENTS We thank Mr. Harrie Gorter and Dr. Stephan Harkema for their helpful insights in XRD analysis and device stack development. We also thank Jack van Glabbeek and Jack Hoppenbrouwer for their help with thermal evaporator and SEM imaging. This work was financially supported by the European Commission through the Horizon 2020 Marie Sklodowska-Curie ITN-INFORM project (Grant Agreement 675867) and by the Spanish Ministry of Economy and Competitiveness (MINECO) via the Unidad de Excelencia María de Maeztu MDM-2015-0538 and MAT201788821-R, M.S. thanks the MINECO for his RyC.

REFERENCES (1) Hutter, E. M.; Eperon, G. E.; Stranks, S. D.; Savenije, T. J. Charge Carriers in Planar and Meso-Structured Organic-Inorganic Perovskites: Mobilities, Lifetimes, and Concentrations of Trap States. Journal of Physical Chemistry Letters 2015, 6, 3082–3090. (2) Stranks, S. D.; Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organic Trihalide Perovskite Absorber. Science 2013, 342, 341– 344. (3) Stranks, S. D.; Snaith, H. J. Metal-Halide Perovskites for Photovoltaic and Light-Emitting Devices. Nature Nanotechnology 2015, 10, 391–402.


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Page 15 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(4) Stranks, S. D.; Burlakov, V. M.; Leijtens, T.; Ball, J. M.; Goriely, A.; Snaith, H. J. Recombination Kinetics in Organic-Inorganic Perovskites: Excitons, Free Charge, and Subgap States. Physical Review Applied 2014, 2, 1–8. (5) Tanaka, K.; Takahashi, T.; Ban, T.; Kondo, T.; Uchida, K.; Miura, N. Comparative Study on the Excitons in Lead-Halide-Based Perovskite-Type Crystals CH3NH3PbBr3 CH3NH 3PbI3. Solid State Communications 2003, 127, 619–623. (6) Sadhanala, A.; Ahmad, S.; Zhao, B.; Giesbrecht, N.; Pearce, P. M.; Deschler, F.; Hoye, R. L. Z.; Gödel, K. C.; Bein, T.; Docampo, P.; Dutton, S. E.; De Volder, M. F. L.; Friend, R. H. BlueGreen Color Tunable Solution Processable Organolead Chloride–Bromide Mixed Halide Perovskites for Optoelectronic Applications. Nano Lett. 2015, 15, 6095–6101. (7) Giacomo, F. D.; Galagan, Y.; Shanmugam, S.; Gorter, H.; Bruele, F. van den; Kirchner, G.; Vries, I. de; Fledderus, H.; Lifka, H.; Veenstra, S.; Aernouts, T.; Groen, P.; Andrissen, R. UpScaling Perovskite Solar Cell Manufacturing from Sheet-to-Sheet to Roll-to-Roll: Challenges and Solutions. Proc. SPIE 10363, Organic, Hybrid, and Perovskite Photovoltaics XVIII 2017, 10363, 103630E. (8) Tan, Z.-K.; Moghaddam, R. S.; Lai, M. L.; Docampo, P.; Higler, R.; Deschler, F.; Price, M.; Sadhanala, A.; Pazos, L. M.; Credgington, D.; Hanusch, F.; Bein, T.; Snaith, H. J.; Friend, R. H. Bright Light-Emitting Diodes Based on Organometal Halide Perovskite. Nature Nanotechnology 2014, 9, 687–692. (9) Cho, H.; Jeong, S.-H.; Park, M.-H.; Kim, Y.-H.; Wolf, C.; Lee, C.-L.; Heo, J. H.; Sadhanala, A.; Myoung, N.; Yoo, S.; Im, S. H.; Friend, R. H.; Lee, T.-W. Overcoming the


15


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Electroluminescence Efficiency Limitations of Perovskite Light-Emitting Diodes. Science 2015, 350, 1222–1225. (10) Schmidt, L. C.; Pertegás, A.; González-Carrero, S.; Malinkiewicz, O.; Agouram, S.; Mínguez Espallargas, G.; Bolink, H. J.; Galian, R. E.; Pérez-Prieto, J. Nontemplate Synthesis of CH3NH3PbBr3 Perovskite Nanoparticles. J. Am. Chem. Soc. 2014, 136, 850–853. (11) Shan, Q.; Song, J.; Zou, Y.; Li, J.; Xu, L.; Xue, J.; Dong, Y.; Han, B.; Chen, J.; Zeng, H. High Performance Metal Halide Perovskite Light-Emitting Diode: From Material Design to Device Optimization. Small 2017, 1701770. (12) Zhang, L.; Yang, X.; Jiang, Q.; Wang, P.; Yin, Z.; Zhang, X.; Tan, H.; Yang, Y. (Michael); Wei, M.; Sutherland, B. R.; Sargent, E. H.; You, J. Ultra-Bright and Highly Efficient Inorganic Based Perovskite Light-Emitting Diodes. Nature Communications 2017, 8, 15640–15640. (13) Qasim, K.; Wang, B.; Zhang, Y.; Li, P.; Wang, Y.; Li, S.; Lee, S. T.; Liao, L. S.; Lei, W.; Bao, Q. Solution-Processed Extremely Efficient Multicolor Perovskite Light-Emitting Diodes Utilizing Doped Electron Transport Layer. Advanced Functional Materials 2017, 27, 1–9. (14) Li, J.; Bade, S. G. R.; Shan, X.; Yu, Z. Single-Layer Light-Emitting Diodes Using Organometal Halide Perovskite/Poly(Ethylene Oxide) Composite Thin Films. Advanced Materials 2015, 27, 5196–5202. (15) Wang, Z.; Cheng, T.; Wang, F.; Dai, S.; Tan, Z. Morphology Engineering for HighPerformance and Multicolored Perovskite Light-Emitting Diodes with Simple Device Structures. Small 2016, 32, 4412–4420.


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(16) Kumawat, N. K.; Gupta, D.; Kabra, D. Recent Advances in Metal Halide-Based Perovskite Light-Emitting Diodes. Energy Technology 2017, 5, 1734–1749. (17) Meng, L.; Yao, E. P.; Hong, Z.; Chen, H.; Sun, P.; Yang, Z.; Li, G.; Yang, Y. Pure Formamidinium-Based Perovskite Light-Emitting Diodes with High Efficiency and Low Driving Voltage. Advanced Materials 2017, 29, 1–7. (18) Wang, J.; Wang, N.; Jin, Y.; Si, J.; Tan, Z. K.; Du, H.; Cheng, L.; Dai, X.; Bai, S.; He, H.; Ye, Z.; Lai, M. L.; Friend, R. H.; Huang, W. Interfacial Control toward Efficient and Low-Voltage Perovskite Light-Emitting Diodes. Advanced Materials 2015, 27, 2311–2316. (19) Yu Chin, X.; Perumal, A.; Bruno, A.; Yantara, N.; Veldhuis, S. A.; Martínez-Sarti, L.; Chandran, B.; Chirvony, V.; Shu-Zee Lo, A.; So, J.; Soci, C.; Graetzel, M.; Bolink, H. J.; Mathews, N.; Mhaisalkar, S. G. Self-Assembled Hierarchical Nanostructured Perovskites Enable Highly Efficient LEDs via Energy Cascade. Energy Environ. Sci 2017, 11, 1770-1778. (20) Xiao, Z.; Kerner, R. A.; Zhao, L.; Tran, N. L.; Lee, K. M.; Koh, T.-W.; Scholes, G. D.; Rand, B. P. Efficient Perovskite Light-Emitting Diodes Featuring Nanometre-Sized Crystallites. Nature Photonics 2017, 11, 108–115. (21) Yuan, M.; Quan, L. N.; Comin, R.; Walters, G.; Sabatini, R.; Voznyy, O.; Hoogland, S.; Zhao, Y.; Beauregard, E. M.; Kanjanaboos, P.; Lu, Z.; Kim, D. H.; Sargent, E. H. Perovskite Energy Funnels for Efficient Light-Emitting Diodes. Nature Nanotechnology 2016, 11, 872-877. (22) Yang, X.; Zhang, X.; Deng, J.; Chu, Z.; Jiang, Q.; Meng, J.; Wang, P.; Zhang, L.; Yin, Z.; You, J. Efficient Green Light-Emitting Diodes Based on Quasi-Two-Dimensional Composition and Phase Engineered Perovskite with Surface Passivation. Nature Communications 2018, 9, 570.


17


Page 18 of 20

(23) Zhao, L.; Yeh, Y.-W.; Tran, N. L.; Wu, F.; Xiao, Z.; Kerner, R. A.; Lin, Y. L.; Scholes, G. D.; Yao, N.; Rand, B. P. In Situ Preparation of Metal Halide Perovskite Nanocrystal Thin Films for Improved Light-Emitting Devices. ACS Nano 2017, 11, 3957–3964. (24) Bi, C.; Wang, Q.; Shao, Y.; Yuan, Y.; Xiao, Z.; Huang, J. Non-Wetting Surface-Driven High-Aspect-Ratio Crystalline Grain Growth for Efficient Hybrid Perovskite Solar Cells. Nature Communications 2015, 6, 7747. (25) Xu, X.; Ma, C.; Cheng, Y.; Xie, Y.-M.; Yi, X.; Gautam, B.; Chen, S.; Li, H.-W.; Lee, C.S.; So, F.; Tsang, S.-W. Ultraviolet-Ozone Surface Modification for Non-Wetting Hole Transport Materials Based Inverted Planar Perovskite Solar Cells with Efficiency Exceeding 18%. Journal of Power Sources 2017, 360, 157–165. (26) Pfuetzner, S.; Petrich, A.; Malbrich, C.; Meiss, J.; Koch, M.; Riede, M. K.; Pfeiffer, M.; Leo, K. Characterisation of Different Hole Transport Materials as Used in Organic P-i-n Solar Cells. Proc. SPIE 6999, Organic Optoelectronics and Photonics III 2008, 6999, 69991M. (27) Ryu, S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Yang, W. S.; Seo, J.; Seok, S. I. Voltage Output of Efficient Perovskite Solar Cells with High Open-Circuit Voltage and Fill Factor. Energy Environ. Sci. 2014, 7, 2614–2618. (28) Henwood, A. F.; Pal, A. K.; Cordes, D. B.; Slawin, A. M. Z.; Rees, T. W.; Momblona, C.; Babaei, A.; Pertegás, A.; Ortí, E.; Bolink, H. J.; Baranoff, E.; Colman, E. Z. Blue-Emitting Cationic Iridium(III) Complexes Featuring Pyridylpyrimidine Ligands and Their Use in Sky-Blue Electroluminescent Devices. Journal of Materials Chemistry C 2017, 5, 9638–9650.


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Page 19 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(29) Xiao, M.; Huang, F.; Huang, W.; Dkhissi, Y.; Zhu, Y.; Etheridge, J.; Gray-Weale, A.; Bach, U.; Cheng, Y.-B.; Spiccia, L. A Fast Deposition-Crystallization Procedure for Highly Efficient Lead Iodide Perovskite Thin-Film Solar Cells. Angew. Chem. Int. Ed. Engl. 2014, 53, 9898–9903. (30) Wang, K. H.; Li, L. C.; Shellaiah, M.; Sun, K. W. Structural and Photophysical Properties of Methylammonium Lead Tribromide (MAPbBr3) Single Crystals. Scientific Reports 2017, 7, 1– 14. (31) Wei, H.; Fang, Y.; Mulligan, P.; Chuirazzi, W.; Fang, H.-H.; Wang, C.; Ecker, B. R.; Gao, Y.; Loi, M. A.; Cao, L.; Huang, J. Sensitive X-Ray Detectors Made of Methylammonium Lead Tribromide Perovskite Single Crystals. Nature Photonics 2016, 10, 333–339. (32) Fang, H.-H.; Adjokatse, S.; Wei, H.; Yang, J.; Blake, G. R.; Huang, J.; Even, J.; Loi, M. A. Ultrahigh Sensitivity of Methylammonium Lead Tribromide Perovskite Single Crystals to Environmental Gases. Science Advances 2016, 2, e1600534. (33) Nguyen, V.-C.; Katsuki, H.; Sasaki, F.; Yanagi, H. Single-Crystal Perovskite CH3NH3PbBr3 Prepared by Cast Capping Method for Light-Emitting Diodes. Jpn. J. Appl. Phys. 2018, 57, 04FL10. (34) Kerner, R. A.; Zhao, L.; Xiao, Z.; Rand, B. P. Ultrasmooth Metal Halide Perovskite Thin Films via Sol–gel Processing. J. Mater. Chem. A 2016, 4, 8308–8315. (35) Yan, K.; Long, M.; Zhang, T.; Wei, Z.; Chen, H.; Yang, S.; Xu, J. Hybrid Halide Perovskite Solar Cell Precursors: Colloidal Chemistry and Coordination Engineering behind Device Processing for High Efficiency. J. Am. Chem. Soc. 2015, 137, 4460–4468.


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Efficient Perovskite Light Emitting Diodes - Effect of Composition

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