Feasible Modification of PEDOT:PSS by Poly(4-styrenesulfonic acid

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Organic Electronic Devices

Feasible Modification of PEDOT:PSS by Poly(4-styrenesulfonic acid): a Universal Method to Double the Efficiencies for Solution-Processed Organic Light-Emitting Devices Yepeng Xiang, Guohua Xie, Qian Li, Longjian Xue, Qian Xu, JunFa Zhu, Yang Tang, Shaolong Gong, Xiaojun Yin, and Chuluo Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b09346 • Publication Date (Web): 19 Jul 2019 Downloaded from pubs.acs.org on July 20, 2019

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ACS Applied Materials & Interfaces

Feasible Modification of PEDOT:PSS by Poly(4styrenesulfonic acid): a Universal Method to Double the Efficiencies for Solution-Processed Organic Light-Emitting Devices Yepeng Xianga,b, Guohua Xiea*, Qian Lic, Longjian Xuec, Qian Xud, Junfa Zhud, Yang Tanga, Shaolong Gonga, Xiaojun Yinb, Chuluo Yanga,b*. aHubei

Key Lab on Organic and Polymeric Optoelectronic Materials, Department of Chemistry,

Wuhan University, Wuhan 430072, China E-mail: [email protected], [email protected] bShenzhen

Key Laboratory of Polymer Science and Technology, College of Materials Science

and Engineering, Shenzhen University, Shenzhen 518060, China. cSchool

of Power and Mechanical Engineering & the Institute of Technological Science, Wuhan

University, South Donghu Road 8, Wuhan 430072, China. dNational

Synchrotron Radiation Laboratory, University of Science and Technology of China,

Hefei, Anhui 230029, China.

ACS Paragon Plus Environment

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ACS Applied Materials & Interfaces 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

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Keywords: PEDOT:PSS; work-function; solution-processed OLEDs; full colors; fluorescence quenching.

Abstract: A feasible, universal, and low-cost strategy for solution-processed organic lightemitting devices (OLEDs) was provided to significant enhance the electroluminescent performances. The commercially available poly(4-styrenesulfonic acid) (PSSA) aqueous solution was mixed into poly(styrene sulfonic acid)-doped poly(3,4-ethylenedioxythiphene) (PEDOT:PSS) to modify its chemical and physical properties. The corresponding work-function can be easily elevated from 5.04 to 5.63 eV. The PSSA modified PEDOT:PSS is found to be a universal method to demonstrate highly efficient OLEDs with different solution-processed host/emitter combinations, covering phosphorescent and thermally activated delayed fluorescence (TADF) devices. The benchmarking solution processed OLEDs based on 2,4,5,6-tetrakis(carbazol-9-yl)1,3-dicyanobenzene

(4CzIPN)

and

bis[2-(4,6-difluorophenyl)pyridinato-

C2,N](picolinato)iridium(III) (FIrpic) achieved the maximum EQEs of 26.6% and 22.4%, respectively, simply by modifying PEDOT:PSS with PSSA, corresponding to the improvement factors of 2.7 and 2.2. It is confirmed that such performances originate simultaneously from reduced interfacial fluorescence quenching, elevated work-function and reduced lateral conduction of the common-used PEDOT:PSS (Clevios P VP Al 4083).

1. Introduction Organic light-emitting diodes (OLEDs) have attracted considerable attentions both in academic and industrial communities during the past few decades. Up to now, OLEDs have been commercialized in many cases, such as smart phones, TV, and solid-state lighting.1 To approach the theoretical electroluminescence (EL) efficiency, many endeavors have been devoted to


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tailoring the structures of the emitting materials with 100% internal quantum efficiencies (IQEs). Phosphorescent emitters involve heavy metals can harvest both singlet and triplet excitons via spin-orbit coupling process, and thus rendering high external quantum efficiencies (EQEs) over 30% for phosphorescent OLEDs (PhOLEDs).2-3 Besides, pure organic thermally activated delayed fluorescence (TADF) emitters have drawn much attention recently due to the unique capability in harvesting triplet excitons via reverse intersystem crossing process (RISC).4-5 To date, the optimized maximum EQEs of the state-of-the-art TADF devices fabricated by vacuum deposition with either red, green, or blue color are exceeding the boundary of 30%, which are comparable with the phosphorescent OLEDs involving heavy-metals.6-8 In general, OLEDs can be fabricated by either high-vacuum deposition or solution-processed. Although stepwise vacuum deposition related to the small molecules can easily achieves the unlimited multilayer structures, the drawbacks should not be ignored, such as severe materials waste, high energy expenditure, and thus high cost. In contrast, solution-processed OLEDs are much more economical regarding cost issues and material utilization.9-10 Among solutionprocessed

OLEDs,

poly(styrene

sulfonic

acid)-doped

poly(3,4-ethylenedioxythiphene)

(PEDOT:PSS) is the most commonly used hole injecting layer, which could favor hole injection and thus high EL performances.11 However, the hole injection barriers from the PEDOT:PSS layer to the emitting layers are typically much higher than the devices fabricated by vacuum deposition with great choice to select a suitable injecting layer. Also, the corrosion and exciton quenching between PEDOT:PSS layer and emitting layer cannot be neglected. To alleviate these drawbacks, many effective methods are applied, such as crosslinked hole transport layer and electrochemical method.9, 12 By introducing the additional hole transport layer, the hole injection barriers can be adjusted and the corrosion and exciton quenching are alleviated. It is reported that


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appropriate modification of PEDOT:PSS can reduce the injection barrier to enable significantly enhanced EL efficiencies of the devices. Lee’s group reported doping polymer perfluorinated ionomer (PFI) in PEDOT:PSS to raise its work function and thus highly efficient green solution processed TADF OLEDs were achieved.13 InCl3 doped PEDOT:PSS was found to a feasible way to obtain high work-function which resulted in considerably high external quantum efficiencies of the solution-processed TADF OLEDs.14 However, the tricky post-process makes it somewhat difficult to easily reproduce the performances and consequently serious performance deviation from batch to batch, which is challenging for quality control in terms of mass production. In this contribution, we introduced a simple strategy to attain high work-function and thus ultra-efficient solution processed OLEDs. By simply mixing two commercially available materials PEDOT:PSS and poly(4-styrenesulfonic acid) (PSSA) without further treatment. The blue device based on the phosphorescent emitter bis[2-(4,6-difluorophenyl)pyridinatoC2,N](picolinato)iridium(III) (FIrpic) achieved a peak EQE of 22.4%, which is outperformed any other previously reported solution-processed devices with the same emitter.15-22 The green device based on the TADF compound 2,4,5,6-tetrakis(carbazol-9-yl)-1,3-dicyanobenzene (4CzIPN) rendered record-high peak EQE of 26.6% which is the champion among the solution-processed green TADF devices.13-14,

23-24

Meanwhile, the red phosphorescent device with bis(2-

methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III)

(Ir(MDQ)2acac),

fabricated

by

solution-process, obtained the EQE of nearly 15%. Notably, these EQEs are the respective ones of the best of the corresponding solution processed OLEDs.17, 25-29 Furthermore, this universal method is found to be not only suitable for different types of emitting materials but also compatible with a wide range of host materials. 2. Experimental Details


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Materials All materials were commercial without further purification. The PSSA solution (18 wt.% in H2O, Mw ~75,000 g/mol) was purchased from Sigma-Aldrich. The PEDOT:PSS (Heraeus Clevios P VP AI 4083) solution, host material of 1,3-bis(carbazol-9-yl)benzene (mCP), electron injecting material lithium 8-hydroxyquinolinolate (Liq), green TADF emitting material of 2,4,5,6-tetrakis(carbazol-9-yl)-1,3-dicyanobenze (4CzIPN) and red TADF emitting material of 2,6-bis[4-(diphenylamino)phenyl]anthraquinone (AQb1) were purchased from Xi’an Polymer Light Technology Corporation. Host materials of 4,4'-bis(carbazol-9-yl)biphenyl (CBP), 9-(4-tert -butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi), hole blocking material of bis[2(diphenylphosphino)phenyl] ether oxide (DPEPO), electron transport material of 1,3,5-tri(mpyrid-3-yl-phenyl)benzene

(TmPyPB),

blue

TADF

emitting

sulfonylbis(4,1-phenylene))bis(9,9-dimethyl-9,10-dihydroacridine) phosphorescent

emitting

material

methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) phosphorescent

emitting

material

of

material

of

10,10'-(4,4'-

(DMAC-DPS), of

(Ir(MDQ)2acac)

red bis(2-

and

blue

bis[2-(4,6-difluorophenyl)pyridinato-C2,

N](picolinato)iridium(III) (FIrpic) were purchased from Luminescence Technology Corporation. The host materials of 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazole-3-carbonitrile (mCPCN) and 2,5-bis(2-(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (o-CzOXD) were synthesized by ourselves according to a modified literature procedure and purified by recrystallization and further gradient sublimation. Device Fabrication Acetone and ethanol was separately used to clean the ITO substrate with ultrasonic bath. The substrates were further dried with N2 flow. After 20 min ultraviolet lightozone (UVO) treatment, PEDOT:PSS or PSSA modified PEDOT:PSS (m-PEDOT:PSS) precursor was spin-coated onto the ITO surface at 4000 rpm. Afterwards, the substrate was


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baked at 120 °C for 10 min in glovebox. Later, the corresponding emitting layer was spin-coated at 1000 rpm and then accompanied with a 40 °C or 50 °C baking process. The corresponding functional materials and aluminum cathode were vacuum deposited step by step under 10-5 mbar. The sealed device was measured in ambient air. 3. Results and Discussions

Figure 1. Photographs of the contact angle measurements on (a, d) PEDOT:PSS, (b, e) PEDOT:PSS-50 wt.% PSSA, and (c, f) PEDOT:PSS-50 wt.% PFI, respectively. H2O and chlorobenzene were used as the testing droplets. Typically, the hole injecting barrier (> 0.6 eV) between PEDOT:PSS and the emitting layer (EML) was rather high and ubiquitous in the solution-processed OLED devices. The PSSA modified PEDOT:PSS (m-PEDOT:PSS) was proposed to tune the work-function and thus lower this barrier. Polymer perfluorinated ionomer (PFI) was reported as a very powerful modifier for PEDOT:PSS.13, 21 Unfortunately, due to the hydrophobic nature of PFI doped PEDOT:PSS (see Figure 1c and 1f), it is very challenging to obtain a uniform film directly on the hole injection layer by using the common chlorobenzene solvent. As shown in Figure 1, the contact angle measurement of PEDOT:PSS which is hydrophilic remained unchanged when doped with PSSA. Herein, the aqueous solution of PSSA was mixed with PEDOT:PSS solution in different weight ratios to screen the optimized recipe for device application. The absorptions of the m-


6

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PEDOT:PSS films prepared with concentration ranging from 10 wt.% to 90 wt.% PSSA were measured. As presented in Figure S1, all the absorptions were very weak in the visible region (400-720 nm). While the concentration below 50 wt.%, the absorptions of the m-PEDOT:PSS films were similar to that of the PEDOT:PSS films. In contrast, when the concentrations were 70 wt.% and 90 wt.%, the shift of the absorption spectrum is attributed to the concentrated component of PSSA. Furthermore, we fabricated the solution-processed OLEDs with the structure of ITO/PEDOT:PSS or m-PEDOT:PSS (10-90 wt.%) (~35 nm)/mCP:4CzIPN (10 wt.%, 60 nm)/ TmPyPB (60 nm)/Liq (1 nm)/Al (devices 1-6) (Figure 2).


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Figure 2. (a) The energy level diagrams and chemical structures of materials for the devices 1-6. (b) Current density-voltage and luminance-voltage curves of the devices. (c) EL spectra of the devices 1-6 at 10 V driving voltage. (d) External quantum efficiency versus current density curves of the devices 1-6. Table 1. Comparison of the device performances without and with PSSA doped PEDOT:PSS. Maximuma

Devic e

Injection layer (PSSA added)

Emitting layer

1

PEDOT:PSS

2

at 2000 cd/m2 CIEb(x, y)

CE, PE, EQE

CE, PE, EQE

mCP: 4CzIPN =90:10

29.4, 11.3, 9.6

28.2, 8.9, 9.2

(0.30, 0.55)

m-PEDOT:PSS (10 wt.%)

mCP: 4CzIPN =90:10

25.3, 8.6, 8.3

24.1, 6.9., 7.9

(0.30, 0.55)

3


mCP: 4CzIPN =90:10

47.0, 18.3, 14.9

40.5, 12.7, 12.9

(0.29, 0.57)

4


mCP: 4CzIPN =90:10

60.2, 23.9, 19.2

50.7, 17.7, 16.1

(0.29, 0.57)

5


mCP: 4CzIPN =90:10

86.2, 33.9, 26.6

73.5, 25.6, 22.7

(0.29, 0.57)

6


mCP: 4CzIPN =90:10

39.6, 12.5, 12.7

NA

(0.29, 0.57)

a)The 1)

maximum efficiencies of current efficiency (CE) (cd A-1), power efficiency (PE) (lm Wand external quantum efficiency (EQE) (%). b)The Commission Internationale de l’Eclairage

When the doping ratio of PSSA was raised, the performances of the corresponding device improved and the maximum EQE of device increased from 9.6% (0 wt.% PSSA) to 26.6% (70 wt.% PSSA). When further adding more PSSA (90 wt.% PSSA), the maximum EQE of the device sharply decreased to 12.7% along with the obvious brightness loss (see Figure 2b and Table 1) Considering the huge improvement of the device performances when using PSSA doped PEDOT:PSS as the injection layer, Ultraviolet photoelectron spectroscopy (UPS) was


8

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represented to acquire the work-function data of m-PEDOT:PSS on the silicon substrate. The curves of UPS are seen in Figure 3a. And the extracted work-function values are summarized in Table 2. There is no doubt that the work-functions of m-PEDOT:PSS increase with the increasing concentration of PSSA. The EL performances based on 4CzIPN are well consistent with the shift of the work-functions. For instance, the work-functions of 50 wt.% and 70 wt.% PSSA doped concentration were 5.59 and 5.63 eV, respectively, which resulted in the peak EQEs of 19.2% and 26.6%. Compared with the pristine PEDOT:PSS, this elevated work-function of mPEDOT:PSS obviosly lowered the exciton barrier from the hole injection layer to the EML (mCP:4CzIPN) which has the highest occupied molecular orbital (HOMO) level of -6.0 eV-a very deep level.13 In contrast, when doped 90 wt.% PSSA, the work-function slightly decreased to 5.54 eV which might be attributed to the unexpected low work-function PSSA itself which dominated in the case. To probe the chemical interaction of PSSA and PEDOT:PSS, X-ray photoelectron spectroscopy (XPS) measurements were performed on different films. The XPS results revealed that once the concentration of PSSA increased, the ratio of PSS/PEDOT increased concurrently, as the signal of S 2p (see Figures 3b and 3c). Meanwhile, it can be concluded that PSSA has some chemical interaction with the pristine PEDOT:PSS rather than simple physical mixing effect (Figure S2).30-32


9


(b)

Normalized Intensity (a.u.)


(a) PSSA

1.0

0 wt.% 10 wt.% 30 wt.% 50 wt.% 70 wt.% 90 wt.% 100 wt.%

0.8 0.6 0.4 0.2 0.0 37

36

35

34

33

PSSA

PSSA

1.0

(c)

S 2p

0 wt.% 10 wt.% 30 wt.% 50 wt.% 70 wt.% 90 wt.% 100 wt.%

0.8 0.6 0.4 0.2

PEDOT

0.0 164

PEDOT

166 168 170 Binding Energy (eV)

Binding Energy (eV)

172

(d) PSSA

0.2

0.1

S 2p

0 wt.% 10 wt.% 30 wt.% 50 wt.% 70 wt.% 90 wt.% 100 wt.%

2E+05 Intensity (a.u.)


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

Page 10 of 28

1441 cm-1

PSSA

0 wt.% 50 wt.% 90 wt.%

1E+05

0.0 164 Binding Energy (eV)

166

1200

1300

1400

1500

1600

Wavenumber (cm-1)

Figure 3. (a) The UPS (under -5 V bias, the exciting energy of the source 40 eV) on secondary electron cutoff on PEDOT:PSS with different concentration of PSSA. (b) S 2p characteristic peaks of m-PEDOT:PSS and PEDOT:PSS in films with different PSSA concentration. (c) Enlarged view of S 2p characteristic curves of m-PEDOT:PSS and PEDOT:PSS from 163 to 166 eV. (d) Raman spectra of the m-PEDOT:PSS and PEDOT:PSS in films with different PSSA concentration. Table 2. Work-functions and lateral conductivities of the films with PSSA doped in PEDOT:PSS and pH of the solutions of PSSA doped PEDOT:PSS. PSSA doped concentration (wt.%)

0.0

10.0

30.0

50.0

70.0

90.0

100.0

Work function (eV)a

5.04

5.22

5.34

5.59

5.63

5.54

4.25


10

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Conductivity (* 10-3 S cm-1)

3.63

1.62

1.24

1.59

4.07

11.27

-

pH

1.60

1.48

1.35

1.18

0.98

0.78

-

a)The

exciting energy of the source is 40 eV.

The inferior performances of the device with the pristine PEDOT:PSS is partially induced by its high lateral conductivity which accounts for the exciton loss and thus the much lower EQE. 14, 33

The lateral conductivities of the m-PEDOT:PSS films decreased initially and increased

subsequently when the PSSA doped concentration gradually increased from 0 wt.% to 90 wt.%. There would be two main reasons accounting for this phenomenon. (1) Via Coulomb force, the conjugation length benzoid chains of PEDOT in the films are surrounded by PSS components and formed coil conformation. When the amount of PSSA gradually increased, the highly conductive component PEDOT and the insulating PSS component is likely to spatially separated and thus rearranged, which lowers the conductivity. This was well keeping with the previous work and XPS results.31 (2) The pH gradually decreased when the concentration of PSSA increased (see Table 2). The hydrogen ion concentration contributed to the enhanced conductivities of the m-PEDOT:PSS, which was similar with acid treatment to the PEDOT:PSS films.34-35 Raman spectroscopy was presented to verify our speculation (see Figure 3d). Raman spectra revealed that when the PSSA doped concentration was increased from 0 wt.% to 50 wt.%, the Raman peaks became more obvious. Combined the wavenumber peak of 1441 cm-1 (benzoid) rather than 1434 cm-1 (quinoid), the lower lateral conductivity can be attributed to the de-doping process and an increasing in the PEDOT conjugation length chains.36-39 Furthermore, when the doped concentration was up to 90 wt.%, the PSSA itself was dominated on the surface to cover the signals of PEDOT. Then the Raman signals became much weaker. The larger lateral conductivity can be attributed to the enhancement of hydrogen ion concentration.40-41 The results of XPS and pH measurements proved this effect in parallel and independently. In brief, the


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overall conductivity originated from the competition of the above-mentioned two processes. Overall, the lateral conductivities of the m-PEDOT:PSS films play a role in ruling the leakage currents (see Table 2). To figure out the effect of PSSA in PEDOT:PSS on the quenching of the EML, the transient photoluminescence spectra were measured. The dilute solution (1 mg/ml) was used to prepare the films in order to probe the interfacial quenching effect. Apparently, all the EML on mPEDOT:PSS displayed similar second-order exponential decays with the prompt and delayed components under degassed condition, which clearly revealed the typical TADF features. Concurrently, the steady photoluminescence spectra and the photoluminescence quantum yields (PLQYs) were measured. As shown in Figure 4 and Table 3, all the steady PL intensities and PLQYs of the EML on m-PEDOT:PSS films were superior to that on the pristine PEDOT:PSS film. To further evidence the difference between m-PEDOT:PSS and PEDOT:PSS, we estimated the rate constants of kr and knr, which represented the radiative decay and non-radiative decay rates, respectively.42 As shown in Table 3, the radiative decay rates were almost same for the case with and without PSSA. However, the introduction of PSSA can efficiently alleviate the non-radiative decay. The non-radiative decay rate of the EML on m-PEDOT:PSS (70 wt.%) is only half of that on the pristine PEDOT:PSS.


12

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Figure 4. The prompt (a) and delayed (b) transient photoluminescence spectra of mCP: 10 wt.% 4CzIPN films on PSSA doped concentration PEDOT:PSS. (c) The steady photoluminescence spectra of mCP: 10 wt.% 4CzIPN films on PSSA doped concentration PEDOT:PSS. (d) Normalized photoluminescence intensities of mCP: 10 wt.% 4CzIPN on PEDOT:PSS with and without PSSA. Table 3. Photophysical properties of mCP: 10 wt.% 4CzIPN on PEDOT:PSS and mPEDOT:PSS Φp/Φdc [%]

kr d [107 s-1]

knr d [107 s-1]

71

24/47

1.32

0.54

2.86

74

25/49

1.31

0.46

19.3

2.87

75

25/50

1.30

0.43

19.9

2.90

81

27/54

1.36

0.32

NO


τp [ns]

τd [μs]

1

PEDOT:PSS

18.1

2.88

2


19.1

3


4


a

a

Φb

[%]


13


Page 14 of 28

5


18.7

2.85

85

29/54

1.55

0.27

6


18.6

2.86

82

27/55

1.45

0.32

a)At

room temperature, the prompt and delayed fluorescence lifetimes of mCP: 10 wt.% 4CzIPN films on PEDOT:PSS with and without PSSA. b)Under oxygen-free condition at room temperature, the PLQYs of mCP: 10 wt.% 4CzIPN on PEDOT:PSS with different concentration of PSSA. c)Under oxygen-free condition, the prompt and delayed fluorescence PLQY. d)At room temperature, the radiative rate constants and non-radiative constants. It is worth noting that the device exhibited significant loss of the luminance (see Figure 2b) when further adding excessive PSSA (90 wt.% PSSA). Although the maximum EQE of 12.7% is still higher than that of the device with the pristine PEDOT:PSS. By combining the pH measurement, XPS results and the lateral conductivity, it is supposed that the excessive mobile ions in PSSA tend to quench the excitons. To further address this suspect, we added acetic acid into the chlorobenzene solution of 4CzIPN to imitate the process occurred in the operating devices. The acetic acid is a weak acid which can provide similar environment in the devices. Additionally, the acetic acid is mutually soluble with chlorobenzene and thus able to avoid some other interference factors. Then we measured steady photoluminescence spectra (see Figure 5). While the acid concentration is below 30 %, the emission intensity slightly decreased compared with the case without adding the acid. In contrast, the emission intensity dropped sharply once the concentration is over 30%. This result is consistent with the trendy of the luminance of the devices with m-PEDOT:PSS. Now it is confirmed that the excessive ions from PSSA account for the luminance loss of the device under EL with high concentration of PSSA doped in PEDOT:PSS.


14

(a)

(b)

AcOH

0% 10 % 20 % 30 % 40 % 50 %

PL intensity (a.u.)

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


400

450

500 550 600 Wavelength (nm)

650

Normalized PL intensity (a.u.)

Page 15 of 28

1.0 0.8 0.6 0.4 0.2 0.0

0

10 20 30 40 AcOH Concentrations (V/V.%)

50

Figure 5. (a) The steady photoluminescence spectra of 4CzIPN solution with different acetic acid (AcOH) doped concentration (V/V.%). (b) Normalized photoluminescence intensities of the 4CzIPN solution with different AcOH concentration (V/V.%). To evidence PSSA doped PEDOT:PSS as a universal and versatile method to significantly enhance the efficiencies of the solution-processed OLEDs, the pristine PEDOT:PSS and mPEDOT:PSS (50 wt.% PSSA) were chosen as the injecting layers for the device with benchmarking phosphorescent and TADF emitters. For clear comparison, the common host mCP was employed. The solution-processed TADF OLEDs were fabricated with the structure of ITO/PEDOT:PSS or m-PEDOT:PSS (50 wt.%) (~35 nm)/mCP:TADF emitter/DPEPO (10 nm)/TmPyPB (50 nm)/Liq (1 nm)/Al (120nm) (device 7-10) (Figure S4a), where the TADF emitters denote AQb1 and DMAC-DPS respectively for red and blue colors.4, 43 In parallel, the phosphorescent devices (see Table 4) employed Ir(MDQ)2acac and FIrpic respectively for red and blue emission.44-45 The blue solution-processed OLEDs based on DAMC-DPS and FIrpic achieved the peak EQEs of 14.2% and 22.4% respectively, which were the highest among the solution-processed OLEDs with the corresponding emitters (Table 4 and Figures S5-S6).15-22, 25, 27, 29


15


Page 16 of 28

In order to determine the compatibility of m-PEDOT:PSS with the other host materials. Several host materials such as hole-transporting type hosts46 and bipolar hosts47-48 were selected to constitute the solution-processed OLEDs (devices 15-22). The devices were fabricated with the common structure of ITO/PEDOT:PSS or m-PEDOT:PSS (50 wt.%) (~35 nm)/Host:4CzIPN (10 wt.%)/TmPyPB (50 nm)/Liq (1 nm)/Al (120nm) (see Table 5 and Figure S4b). It is evident that all the devices involved m-PEDOT:PSS were superior to those with the pristine PEDOT:PSS as the injection layer. Remarkably, the device 16 based on CBP:10 wt.% 4CzIPN achieved a high peak EQE of 25.2% (Table 5 and Figure S7). Table 4. OLED properties base on different emitting materials. Maximum


Emitting layer

7

PEDOT:PSS

mCP: AQb1 =90:10

3.8, 2.1, 3.7

(0.62, 0.37)

8


mCP: AQb1 =90:10

8.8, 5.6, 8.6

(0.61, 0.39)

9

PEDOT:PSS

mCP: DMAC-DPS =80:20

15.2, 8.7, 8.2

(0.17, 0.27)

10


mCP: DMAC-DPS =80:20

29.3, 18.4, 14.8

(0.17, 0.31)

11

PEDOT:PSS

mCP: Ir(MQD)2acac =90:10

11.1, 3.6, 6.9

(0.60, 0.39)

12


mCP: Ir(MQD)2acac =90:10

22.0, 7.7, 14.1

(0.61, 0.39)

13

PEDOT:PSS

mCP: FIrpic =90:10

20.4, 5.8, 10.3

(0.17, 0.34)

14


mCP: FIrpic =90:10

44.5 14.7, 22.4

(0.17, 0.36)

Device

a)The

CIEa(x, y) CE, PE, EQE

Commission Internationale de l’Eclairage coordinates recorded at around 1000 cd m-2.

Table 5. Comparison of the devices with different host materials.


16

Page 17 of 28 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


Maximum


Emitting layer

15

PEDOT:PSS

CBP:4CzIPN =90:10

34.4, 15.8, 10.9

(0.31, 0.55)

16


CBP:4CzIPN =90:10

78.0, 41.8, 25.2

(0.29, 0.55)

17

PEDOT:PSS

CzSi:4CzIPN =90:10

14.3, 3.0, 5.6

(0.30, 0.54)

18


CzSi:4CzIPN =90:10

23.3, 6.2, 7.7

(0.29, 0.55)

19

PEDOT:PSS

o-CzOXD:4CzIPN =90:10

34.4, 11.4, 10.7

(0.31, 0.57)

20


o-CzOXD:4CzIPN =90:10

62.6, 25.2, 19.7

(0.29, 0.56)

21

PEDOT:PSS

mCPCN:4CzIPN =90:10

26.2, 7.6, 8.7

(0.30, 0.54)

22


mCPCN:4CzIPN =90:10

34.6 14.9, 11.7

(0.28, 0.54)

Device

a)The

CIEa(x, y) CE, PE, EQE

Commission Internationale de l’Eclairage coordinates recorded at around 1000 cd m-2.

It is clear that the modification of PEDOT:PSS (Clevios P VP AI 4083) with PSSA is simple but effective. No further treatment is required as m-PEDOT:PSS can be feasibly obtained by mixing the two solutions. The green and blue solution-processed OLEDs with PSSA doped PEDOT:PSS were the champion devices ever reported (see Table S2). Moreover, the film of the m-PEDOT:PSS was kept hydrophilic, unlike the PFI modified PEDOT:PSS film which was hydrophobic owing to the polyvinyl fluoride backbones. Also, since the strongly acidic nature of PEDOT:PSS and m-PEDOT:PSS may etch the ITO electrode to the similar extent. Therefore, In and Sn species may diffuse into the emitting layer and consequently affect the device lifetime. The XPS measurements were introduced to figure out the influence (see Figure S8). After dipping the ITO substrate into the PEDOT:PSS 4083 solution and m-PEDOT:PSS (50 wt.% PSSA) solution for 2 hours, the In 3d and Sn 3d characteristic peaks of the ITO electrode were descended compared with the reference. Nevertheless, the diffusion of In and Sn under EL


17


Page 18 of 28

process can be inhibited by some other approach based on the previous work.49 This ITO etching experiment is not exactly the same situation as the real device. How much the modified PEDOT:PSS will deteriorate or improve the stability under EL process will be further investigated in the near future. 4. Conclusions In summary, a simple PSSA doping strategy was developed to attain high work-function and hydrophilic surface to achieve highly efficient red, green, and blue OLEDs via solution process. The work-function of PEDOT:PSS can be easily elevated from 5.04 to 5.63 eV. An optimized amount of PSSA in PEDOT:PSS in beneficial to reduce fluorescence quenching of the emitters and leakage current of the devices. The solution processed OLEDs based on 4CzIPN and FIrpic achieved the record-high EQEs of 26.6% and 22.4%, respectively. This work demonstrates the great potential of the applications of PSSA modified PEDOT:PSS in solution-processed optoelectronics. ASSOCIATED CONTENT Supporting Information The absorption, XPS and lateral conductivity measurement of the films of PEDOT:PSS and mPEDOT:PSS. The solution-processed device performances based different host/emitter combinations, covering phosphorescent and thermally activated delayed fluorescence (TADF) devices, are supplied as Supporting Information. These are available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author


18

Page 19 of 28 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


* Email: [email protected]. (Guohua Xie) * Email: [email protected]. (Chuluo Yang) Notes The authors declare no competing financial interest. Acknowledgements We acknowledge financial support from the National Key Research and Development Program (2016YFB0401002 and 2018YFB1105100), the National Natural Science Foundation of China (No.

51873159,

51573141,

61575146

and

51503156),

Shenzhen

Peacock

Plan

(KQTD20170330110107046), the Key Technological Innovation Program of Hubei Province (No. 2018AAA013), the Natural Science Foundation of Hubei Province (No. 2017CFB687). The BL11U beamline in the National Synchrotron Radiation Laboratory (NSRL) in Hefei is gratefully acknowledged for providing the beam time. G. X. acknowledge the funding support from Large-scale Instrument and Equipment Sharing Foundation of Wuhan University. References (1) Zhu, M.; Hu, N.; Han, S.; Kim, J. Advances in OLED Emitting and Pixel Define Materials. SID Int. Symp., Dig. Tech. Pap. 2018, 49, 14-15. (2) Kim, K.-H.; Kim, J.-J. Origin and Control of Orientation of Phosphorescent and TADF Dyes for High-Efficiency OLEDs. Adv. Mater. 2018, 30, 1705600. (3) Baldo, M. A.; O'Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.; Thompson, M. E.; Forrest, S. R. Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices. Nature 1998, 395, 151-154.


19


Page 20 of 28

(4) Zhang, Q.; Li, B.; Huang, S.; Nomura, H.; Tanaka, H.; Adachi, C. Efficient Blue Organic Light-Emitting Diodes Employing Thermally Activated Delayed Fluorescence. Nat. Photonics 2014, 8, 326-332. (5) Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Highly Efficient Organic Light-Emitting Diodes from Delayed Fluorescence. Nature 2012, 492, 234-238. (6) Zeng, W.; Lai, H.-Y.; Lee, W.-K.; Jiao, M.; Shiu, Y.-J.; Zhong, C.; Gong, S.; Zhou, T.; Xie, G.; Sarma, M.; Wong, K.-T.; Wu, C.-C.; Yang, C. Achieving Nearly 30% External Quantum Efficiency for Orange-Red Organic Light Emitting Diodes by Employing Thermally Activated Delayed Fluorescence Emitters Composed of 1,8-Naphthalimide-Acridine Hybrids. Adv. Mater. 2018, 30, 1704961. (7) Ahn, D. H.; Kim, S. W.; Lee, H.; Ko, I. J.; Karthik, D.; Lee, J. Y.; Kwon, J. H. Highly Efficient Blue Thermally Activated Delayed Fluorescence Emitters Based on Symmetrical and Rigid Oxygen-Bridged Boron Acceptors. Nat. Photonics 2019, DOI: 10.1038/s41566-019-04155. (8) Wu, T. L.; Huang, M. J.; Lin, C. C.; Huang, P. Y.; Chou, T. Y.; Chen-Cheng, R. W.; Lin, H. W.; Liu, R. S.; Cheng, C. H. Diboron Compound-Based Organic Light-Emitting Diodes with High Efficiency and Reduced Efficiency Roll-Off. Nat. Photonics 2018, 12, 235-243. (9) Tsai, K. W.; Hung, M. K.; Mao, Y. H.; Chen, S. A. Solution‐Processed Thermally Activated Delayed Fluorescent OLED with High EQE as 31% Using High Triplet Energy Crosslinkable Hole Transport Materials. Adv. Funct. Mater. 2019, 29, 1901025.


20

Page 21 of 28 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


(10) Zou, Y.; Gong, S.; Xie, G.; Yang, C. Design Strategy for Solution-Processable Thermally Activated Delayed Fluorescence Emitters and Their Applications in Organic Light-Emitting Diodes. Adv. Opt. Mater. 2018, 6, 1800568. (11) Wong, M. Y.; Zysman-Colman, E. Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes. Adv. Mater. 2017, 29, 1605444. (12) Yu, T.; Xu, J.; Liu, L.; Ren, Z.; Yang, W.; Yan, S.; Ma, Y. Electrochemically Deposited Interlayer Between PEDOT:PSS and Phosphorescent Emitting Layer for Multilayer SolutionProcessed Phosphorescent OLEDs. J. Mater. Chem. C 2016, 4, 9509-9515. (13) Kim, Y.-H.; Wolf, C.; Cho, H.; Jeong, S.-H.; Lee, T.-W. Highly Efficient, Simplified, Solution-Processed Thermally Activated Delayed-Fluorescence Organic Light-Emitting Diodes. Adv. Mater. 2016, 28, 734-741. (14) Zhou, T.; Xie, G.; Gong, S.; Huang, M.; Luo, J.; Yang, C. Simple InCl3 Doped PEDOT:PSS and UV-Ozone Treatment Strategy: External Quantum Efficiency up to 21% for Solution-Processed Organic Light-Emitting Devices with a Thermally Activated Delayed Fluorescence Emitter. ACS Appl. Mater. Interfaces 2017, 9, 34139-34145. (15) Sun, D.; Zhou, X.; Liu, J.; Sun, X.; Li, H.; Ren, Z.; Ma, D.; Bryce, M. R.; Yan, S. Solution-Processed Blue/Deep Blue and White Phosphorescent Organic Light-Emitting Diodes (PhOLEDs)

Hosted

by

a

Polysiloxane

Derivative

with

Pendant

mCP

(1,3-bis(9-

carbazolyl)benzene). ACS Appl. Mater. Interfaces 2015, 7, 27989-27998.


21


Page 22 of 28

(16) Ye, S.; Liu, Y.; Chen, J.; Lu, K.; Wu, W.; Du, C.; Liu, Y.; Wu, T.; Shuai, Z.; Yu, G. Solution-Processed Solid Solution of a Novel Carbazole Derivative for High-Performance Blue Phosphorescent Organic Light-Emitting Diodes. Adv. Mater. 2010, 22, 4167-4171. (17) Chen, J.; Shi, C.; Fu, Q.; Zhao, F.; Hu, Y.; Feng, Y.; Ma, D. Solution-Processable Small Molecules as Efficient Universal Bipolar Host for Blue, Green and Red Phosphorescent Inverted OLEDs. J. Mater. Chem. 2012, 22, 5164-5170. (18) Jiang, W.; Duan, L.; Qiao, J.; Zhang, D.; Dong, G.; Wang, L.; Qiu, Y. Novel Star-Shaped Host Materials for Highly Efficient Solution-Processed Phosphorescent Organic Light-Emitting Diodes. J. Mater. Chem. 2010, 20, 6131-6137. (19) Aizawa, N.; Pu, Y.-J.; Watanabe, M.; Chiba, T.; Ideta, K.; Toyota, N.; Igarashi, M.; Suzuri, Y.; Sasabe, H.; Kido, J. Solution-Processed Multilayer Small-Molecule Light-Emitting Devices with High-Efficiency White-Light Emission. Nat. Commun. 2014, 5, 5756-5766. (20) Feng, Y.; Lu, T.; Liu, D.; Jiang, W.; Sun, Y. High-Performance Blue Phosphorescent and Thermally Activated Delayed Fluorescent Solution-Processed OLEDs Based on Exciplex Host by Modifying TCTA. Org. Electron. 2019, 67, 136-140. (21) Han, T.-H.; Choi, M.-R.; Jeon, C.-W.; Kim, Y.-H.; Kwon, S.-K.; Lee, T.-W. UltrahighEfficiency Solution-Processed Simplified Small-Molecule Organic Light-Emitting Diodes Using Universal Host Materials. Sci. Adv. 2016, 2, e1601428. (22) Zhang, Y.-X.; Wang, B.; Yuan, Y.; Hu, Y.; Jiang, Z.-Q.; Liao, L.-S. Solution-Processed Thermally Activated Delayed Fluorescence Exciplex Hosts for Highly Efficient Blue Organic Light-Emitting Diodes. Adv. Opt. Mater. 2017, 5, 1700012.


22

Page 23 of 28 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


(23) Cho, Y. J.; Yook, K. S.; Lee, J. Y. High Efficiency in a Solution-Processed Thermally Activated Delayed-Fluorescence Device Using a Delayed-Fluorescence Emitting Material with Improved Solubility. Adv. Mater. 2014, 26, 6642-6646. (24) Komatsu, R.; Sasabe, H.; Inomata, S.; Pu, Y.-J.; Kido, J. High Efficiency Solution Processed OLEDs Using a Thermally Activated Delayed Fluorescence Emitter. Synth. Met. 2015, 202, 165-168. (25) Xie, G.; Chen, D.; Li, X.; Cai, X.; Li, Y.; Chen, D.; Liu, K.; Zhang, Q.; Cao, Y.; Su, S.-J. Polarity-Tunable Host Materials and Their Applications in Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes. ACS Appl. Mater. Interfaces 2016, 8, 2792027930. (26) Liu, X.; Yao, B.; Zhang, Z.; Zhao, X.; Zhang, B.; Wong, W.-Y.; Cheng, Y.; Xie, Z. Power-Efficient Solution-Processed Red Organic Light-Emitting Diodes Based on an Exciplex Host and a Novel Phosphorescent Iridium Complex. J. Mater. Chem. C 2016, 4, 5787-5794. (27) Luo, J.; Gong, S.; Gu, Y.; Chen, T.; Li, Y.; Zhong, C.; Xie, G.; Yang, C. Multi-Carbazole Encapsulation as a Simple Strategy for the Construction of Solution-Processed, Non-Doped Thermally Activated Delayed Fluorescence Emitters. J. Mater. Chem. C 2016, 4, 2442-2446. (28) Yao, B.; Lin, X.; Zhang, B.; Wang, H.; Liu, X.; Xie, Z. Power-Efficient and SolutionProcessed Red Phosphorescent Organic Light-Emitting Diodes by Choosing Combinations of Small Molecular Materials to Form a Well-Dispersed Exciplex Co-Host. J. Mater. Chem. C 2018, 6, 4409-4417.


23


Page 24 of 28

(29) Wu, K.; Wang, Z.; Zhan, L.; Zhong, C.; Gong, S.; Xie, G.; Yang, C. Realizing Highly Efficient Solution-Processed Homojunction-Like Sky-Blue OLEDs by Using Thermally Activated Delayed Fluorescent Emitters Featuring an Aggregation-Induced Emission Property. J. Phys. Chem. Lett. 2018, 9 (7), 1547-1553. (30) Lee, T.-W.; Chung, Y. Control of the Surface Composition of a Conducting-Polymer Complex Film to Tune the Work Function. Adv. Funct. Mater. 2008, 18, 2246-2252. (31) Stöcker, T.; Köhler, A.; Moos, R. Why Does the Electrical Conductivity in PEDOT:PSS Decrease with PSS Content? a Study Combining Thermoelectric Measurements with Impedance Spectroscopy. J. Polym. Sci. Pol. Phys. 2012, 50, 976-983. (32) Modarresi, M.; Franco-Gonzalez, J. F.; Zozoulenko, I. Computational Microscopy Study of the Granular Structure and pH Dependence of PEDOT:PSS. Phys. Chem. Chem. Phys. 2019, 21, 6699-6711. (33) Hu, L.; Fu, J.; Yang, K.; Xiong, Z.; Wang, M.; Yang, B.; Wang, X.; Tang, X.; Zang, Z.; Li, M.; Li, J.; Sun, K. Inhibition of In-Plane Charge Transport in Hole Transfer Layer to Achieve High Fill Factor for Inverted Planar Perovskite Solar Cells. Solar RRL. 2019, DOI: 10.1002/solr.201900104. (34) Shi, H.; Liu, C.; Jiang, Q.; Xu, J. Effective Approaches to Improve the Electrical Conductivity of PEDOT:PSS: A Review. Adv. Electron. Mater. 2015, 1, 1500017. (35) Wang, H.; Ail, U.; Gabrielsson, R.; Berggren, M.; Crispin, X. Ionic Seebeck Effect in Conducting Polymers. Adv. Energy. Mater. 2015, 5, 1500044.


24

Page 25 of 28 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


(36) Jönsson, S. K. M.; Birgerson, J.; Crispin, X.; Greczynski, G.; Osikowicz, W.; Denier van der Gon, A. W.; Salaneck, W. R.; Fahlman, M. The Effects of Solvents on the Morphology and Sheet Resistance in Poly(3,4-ethylenedioxythiophene)-Polystyrenesulfonic Acid (PEDOT-PSS) Films. Synth. Met. 2003, 139, 1-10. (37) De Kok, M. M.; Buechel, M.; Vulto, S. I. E.; Van de Weijer, P.; Meulenkamp, E. A.; de Winter, S. H. P. M.; Mank, A. J. G.; Vorstenbosch, H. J. M.; Weijtens, C. H. L.; van Elsbergen, V. Modification of PEDOT:PSS as Hole Injection Layer in Polymer LEDs. Phys. Stat. Sol. (a) 2004, 201, 1342-1359. (38) Nardes, A. M.; Kemerink, M.; Janssen, R. A. J.; Bastiaansen, J. A. M.; Kiggen, N. M. M.; Langeveld, B. M. W.; van Breemen, A. J. J. M.; de Kok, M. M. Microscopic Understanding of the Anisotropic Conductivity of PEDOT:PSS Thin Films. Adv. Mater. 2007, 19, 1196-1200. (39) Thomas, J. P.; Zhao, L.; McGillivray, D.; Leung, K. T. High-Efficiency Hybrid Solar Cells by Nanostructural Modification in PEDOT:PSS with Co-Solvent Addition. J. Mater. Chem. A 2014, 2, 2383-2389. (40) Lee, T.-W.; Chung, Y.; Kwon, O.; Park, J.-J. Self-Organized Gradient Hole Injection to Improve the Performance of Polymer Electroluminescent Devices. Adv. Funct. Mater. 2007, 17, 390-396. (41) Yeon, C.; Yun, S. J.; Kim, J.; Lim, J. W. PEDOT:PSS Films with Greatly Enhanced Conductivity via Nitric Acid Treatment at Room Temperature and Their Application as Pt/TCOFree Counter Electrodes in Dye-Sensitized Solar Cells. Adv. Electron. Mater. 2015, 1, 1500121.


25


Page 26 of 28

(42) Hamze, R.; Peltier, J. L.; Sylvinson, D.; Jung, M.; Cardenas, J.; Haiges, R.; Soleilhavoup, M.; Jazzar, R.; Djurovich, P. I.; Bertrand, G.; Thompson, M. E. Eliminating Nonradiative Decay in Cu(I) Emitters: >99% Quantum Efficiency and Microsecond Lifetime. Science 2019, 363, 601-606. (43) Zhang, Q.; Kuwabara, H.; Potscavage, W. J.; Huang, S.; Hatae, Y.; Shibata, T.; Adachi, C. Anthraquinone-Based Intramolecular Charge-Transfer Compounds: Computational Molecular Design,

Thermally

Activated

Delayed

Fluorescence,

and

Highly

Efficient

Red

Electroluminescence. J. Am Chem. Soc. 2014, 136, 18070-18081. (44) Duan, J. P.; Sun, P. P.; Cheng, C. H. New Iridium Complexes as Highly Efficient OrangeRed Emitters in Organic Light-Emitting Diodes. Adv. Mater. 2003, 15, 224-228. (45) Adachi, C.; Kwong, R. C.; Djurovich, P.; Adamovich, V.; Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Endothermic Energy Transfer: A Mechanism for Generating Very Efficient High-Energy Phosphorescent Emission in Organic Materials. Appl. Phys. Lett. 2001, 79, 20822084. (46) Zhou, G.; Wong, W.-Y.; Yao, B.; Xie, Z.; Wang, L. Triphenylamine-Dendronized Pure Red Iridium Phosphors with Superior OLED Efficiency/Color Purity Trade-Offs. Angew. Chem. Int. Ed. 2007, 46, 1149-1151. (47) Tao, Y.; Wang, Q.; Yang, C.; Wang, Q.; Zhang, Z.; Zou, T.; Qin, J.; Ma, D. A Simple Carbazole/Oxadiazole Hybrid Molecule: an Excellent Bipolar Host for Green and Red Phosphorescent OLEDs. Angew. Chem. Int. Ed. 2008, 47, 8104-8107.


26

Page 27 of 28 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


(48) Tsai, W.-L.; Huang, M.-H.; Lee, W.-K.; Hsu, Y.-J.; Pan, K.-C.; Huang, Y.-H.; Ting, H.C.; Sarma, M.; Ho, Y.-Y.; Hu, H.-C.; Chen, C.-C.; Lee, M.-T.; Wong, K.-T.; Wu, C.-C. A Versatile Thermally Activated Delayed Fluorescence Emitter for Both Highly Efficient Doped and Non-Doped Organic Light Emitting Devices. Chem. Commun. 2015, 51, 13662-13665. (49) Ahn, S.; Park, M.-H.; Jeong, S.-H.; Kim, Y.-H.; Park, J.; Kim, S.; Kim, H.; Cho, H.; Wolf, C.; Pei, M.; Yang, H.; Lee, T.-W. Fine Control of Perovskite Crystallization and Reducing Luminescence Quenching Using Self-Doped Polyaniline Hole Injection Layer for Efficient Perovskite Light-Emitting Diodes. Adv. Funct. Mater. 2019, 29, 1807535.


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Table of contents


28

Feasible Modification of PEDOT:PSS by Poly(4-styrenesulfonic acid

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