An Alkane-Soluble Dendrimer as Electron-Transport Layer in Polymer

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An alkane soluble dendrimer as electron transport layer in polymer light-emitting diodes Zhiming Zhong, Sen Zhao, Jian Pei, Jian Wang, Lei Ying, Junbiao Peng, and Yong Cao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05172 • Publication Date (Web): 20 Jul 2016 Downloaded from http://pubs.acs.org on July 22, 2016

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ACS Applied Materials & Interfaces

An Alkane Soluble Dendrimer as Electron Transport Layer in Polymer Light-Emitting Diodes Zhiming Zhong †, Sen Zhao †, Jian Pei ‡, Jian Wang †*, Lei Ying †*, Junbiao Peng †, and Yong Cao † †Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, P. R. China ‡Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China KEYWORDS: polymer light emitting diodes, solution process, multilayer device, alkane soluble, electron transport

ABSTRACT

Polymer light-emitting diodes (PLEDs) have attracted broad interest due to their solutionprocessable properties. It is well known that to achieve better performance, organic lightemitting diodes require multilayer device structures. However, it is difficult to realize multilayer device structures by solution processing for PLEDs. Because most semiconducting polymers

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have similar solubility in common organic solvents, such as toluene, xylene, chloroform and chlorobenzene, the deposition of multilayers can cause layers to mix together and damage each layer. Herein, a novel semi-orthogonal solubility relationship has been developed and demonstrated. For the first time, an alkane-soluble dendrimer is utilized as the electron transport layer (ETL) in PLEDs via a solution-based process. With the dendrimer ETL, the external quantum efficiency increases more than three-fold. This improvement in the device performance is attributed to better exciton confinement, improved exciton energy transfer, and better charge carrier balance. The semi-orthogonal solubility provided by alkane offers another process dimension in PLEDs. By combining them with water/alcohol-soluble polyelectrolytes, more exquisite multilayer devices can be fabricated to achieve high device performance, and new device structures can be designed and realized.

INTRODUCTION The solution-processable polymer semiconductors have advantages over traditional inorganic semiconductors and non-solution-processable organic semiconductors in fabricating low-cost, large-area, and flexible devices.1-4 One of the major applications of the polymer semiconductors is in polymer light-emitting diodes (PLEDs) used in displays and solid-state lightings.4-5 It is well known that to achieve better performance, organic light-emitting diodes (OLED) require multilayer device structures.6-7 For small-molecule OLEDs, it is easy to realize multilayer device structures through high vacuum thermal evaporation. However, it is extremely difficult to fabricate PLEDs with multilayer device structures by solution processing methods.8-10 Because most semiconducting polymers have similar solubility in common organic solvents, such as


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toluene, xylene, chloroform and chlorobenzene, the deposition of multilayers can cause layers to mix together and damage each layer.11-12 Many approaches have been developed to overcome this problem. For example, crosslinkable semiconducting molecules have been synthesized, and they can form robust films with excellent solvent resistance after the thermo-, proton- or photo-crosslinking process.8, 11, 13-16 Another approach is to develop water/alcohol-soluble molecules. Due to their total orthogonal solubility with the common semiconducting polymers, the water/alcohol-soluble molecules are widely used as electron transporting layers (ETLs) in PLEDs and organic photovoltaic devices (OPVs).910, 17

In reality, the solubility of the organic semiconductor materials cannot be simply classified as “polar” or “nonpolar”. There is a semi-orthogonal solubility between the orthogonal and parallel relationships. For example, the high molecular weight (Mw) poly (9-vinylcarbazole) (PVK, from Sigma-Aldrich, with an average Mw of ~1,100,000) has good solubility in chlorobenzene but poor solubility in p-xylene, which makes it one of the most popular solution-processable hole transport layers (HTLs) and electron blocking layers (EBLs) in PLEDs because most light emitting polymers are processed from p-xylene solution.6, 18-23 In OPVs, by taking advantage of the solubility difference between the donor polymer and [6,6]-phenyl C61/71 butyric acid methyl ester (PCBM), sequential processing of the donor polymer layer and the PCBM layer is possible, which results in a gradient bulk heterojunction morphology after annealing.24-25 In our contribution, a novel semi-orthogonal solubility relationship in PLEDs is proposed and demonstrated for the first time by using an alkane-soluble dendrimer as the ETL. Generally, the conjugated polymer has poor solubility in the alkane solvent mainly because the inert alkane


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molecules have a weaker interaction with the conjugated backbones than the π-π interaction of the conjugated backbones themselves. Therefore, the resultant solids are usually purified by Soxhlet extraction using n-hexane as the eluent to remove the small molecular weight fractions after polymerization.26-29 In other words, the alkane-soluble molecules have the potential to be processed on top of the conjugated polymer films without damaging the polymer layer. For example, the molecule G0 (Figure 1) is a π-conjugated stilbenoid-based dendrimer with a molecule weight of 4368 Da.30 The branched molecular structure and the 24 n-hexyls make G0 highly soluble in alkane (> 200 mg/mL in n-hexane and n-octane, > 100 mg/mL in n-C12H26 and n-C16H34). In addition to the unique solubility, G0 shows the optoelectronic properties required for efficient ETLs, such as the appropriate energy levels, a large energy gap, and good electron transport ability (after annealing).18, 31 The combination of the alkane solubility and the compatible optoelectronic properties makes it possible to sequentially solution process G0 as the ETL in PLEDs. With G0 as the ETL in a dithienyl-benzothiadiazole (DBT, variously abbreviated as DTBT and TBT)-based PLED, the maximum luminous efficiency (LEmax) increase by more than 300%.


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Figure 1. The molecular structures of G0 and PPF-SO15-DBT1. EXPERIMENTAL SECTION Materials. The conjugated polymer poly((alkoxyphenyl-substituted)fluorene-co-( dibenzothiophene-S,S-dioxide)-co-(4,7-dithienyl-benzothiadiazole)) (PPF-SO15-DBT1, consisting of PF:SO:DBT with a molar feed ratio of 84:15:1) was synthesized in our laboratory and purified by Soxhlet extraction using methanol and n-hexane as the eluents. The alkyl side chain of the DBT (variously abbreviated as DTBT and TBT) unit was a little different from the PPF-SO-DHTBT used in Ref. 20. The G0 dendrimer was also synthesized in our laboratory by following the process detailed in Ref. 30. Figure S1 shows the cyclic voltammogram measurements of both PPF-SO15-DBT1 and G0. PEDOT:PSS (CLEVIOS™ P VP AI 4083) was


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purchased from Heraeus Electronic Materials Division. All solvents were purchased from SigmaAldrich and used as received unless otherwise noted. Device Fabrication. Indium tin oxide (ITO)-coated glass (from China Southern Glass Holding Corp.) with a sheet resistance of 15-20 Ω per square was used as the substrate. Prior to device fabrication, the substrates were thoroughly cleaned in sequence in an ultrasonic bath of acetone, isopropanol, detergent, de-ionized water and isopropanol, and dried in a vacuum baking oven. After a 20 minute oxygen plasma treatment, a 40 nm-thick PEDOT:PSS layer was first spincoated on the ITO substrate, baked at 180 °C in nitrogen for 10 minutes and then cooled down to room temperature. A 35 or 70 nm PPF-SO15-DBT1 layer was spin-coated on top of the PEDOT:PSS layer using 8 or 12 mg mL-1 p-xylene solution. Subsequently, the n-C12H26 or a 35 nm G0 layer was spin-coated on top of PPF-SO15-DBT1 from 30 mg mL-1 n-C12H26 solution after filtered by a 0.22 µm PTFE filter, and then the flims were annealed at 100 °C for 20 minutes in nitrogen. Finally, 4 nm of barium followed by 150 nm of aluminum were thermally evaporated with a shadow mask to form the top electrode at a pressure of 10-4 Pa. The device area is 15 ± 0.1 mm2, defined by the overlap between the patterned ITO and the cathode. To fabricate the electron-dominant devices, 50 nm of Al was thermally deposited on ITO with the same pattern at a pressure of 10-4 Pa. The subsequent layers were deposited with the same process described for the regular devices. Device Characterization. The thickness of the organic films was determined by a Dektak 150 surface profiler. The J-V-L characteristics were measured by a Keithley 236 source meter and a silicon photodiode calibrated by a Konica Minolta Chroma Meter CS-200. The electroluminescence spectra and CIE coordinates were taken using a Photo Research PR-705


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spectrometer. The absorption spectra of films were measured by a Shimadzu UV3600. The AFM height images were scanned by a Bruker Multimode 8 in ScanAsyst mode. RESULTS AND DISCUSSION Solvent rinsing test. In principle, ETLs are necessary in devices with a low electron mobility light-emitting layer (EML) and/or in devices with a recombination zone close to the cathode. The performance of DBT-based PLEDs is usually sensitive to the electron transport capability of the device which will be discussed in Section 3. To fully realize G0’s electron transporting potential, the red emitting polymer PPF-SO15-DBT1 (Figure 1), with an electron mobility of ~ 1.1 × 10-13 cm2 V-1 s-1 (Figure S4) is chosen as the model conjugated polymer. By comparison, the electron mobility of G0 is approximately 5.1 × 10-7 cm2 V-1 s-1 (Fig. S4), which is five orders of magnitude larger than that of the EML. The alkane solvent for G0 is n-C12H26. To verify the semi-orthogonal solubility relationship, a solvent rinsing test has to be carried out. In PLEDs, the organic function layers are typically less than 100 nm thick; they are easily damaged by solvent. Re-dissolution happens if the solvents are not orthogonal. Even though the orthogonal solvent is used, it can be washed away during spin-coating if the molecules do not have enough adhesion.32-33 To test the solvent resistance of the light emission layer, 60 µL of n-C12H26 was spin-coated (for 60 seconds at 2000 rotations per minute) onto the 35 nm PPF-SO15-DBT1 thin film. The thickness variation was observed by UV-visible absorption measurements.11-12 As shown in Figure 2, the PPF-SO15-DBT1 film retains ~ 97% of its original thickness after the n-C12H26 rinse.


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Figure 2. The UV-visible absorption spectra of the PPF-SO15-DBT1 film before and after the nC12H26 rinse. The main absorption peak of the PPF-SO15-DBT1 is contributed by the 15 mol% SO units and 84 mol% PPF units. The surface morphology of the films was further investigated by atomic force microscopy (AFM). Figure 3 shows the height images of the PPF-SO15-DBT1 film before and after the nC12H26 rinse. The root-mean-square roughness (Rrms) of the pristine film is 0.535 nm, while the Rrms of the rinsed film is 0.549 nm. Rinsing the PPF-SO15-DBT1 with the n-C12H26 solvent does not have an obvious impact on both the film thickness and the interface morphology. As a result, G0 can be deposited on top of PPF-SO15-DBT1 using the n-C12H26 solvent.


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Figure 3. The AFM height images of the PPF-SO15-DBT1 a) before and b) after the n-C12H26 rinse. PLEDs with G0 ETL. The PLED device was fabricated with the configuration of ITO/PEDOT:PSS (40 nm)/PPF-SO15-DBT1 (35 nm)/G0 (35 nm)/Ba/Al. For the control device without the G0 ETL, a 70 nm PPF-SO15-DBT1 layer is used to maintain the same total device thickness. In addition, a control device that has undergone a solvent treatment, i.e., spin-coating the n-C12H26 on top of the PPF-SO15-DBT1 to account for the potential solvent effect, was also fabricated.34-36 The schematic of the device structure is illustrated in Figure 4a. The luminous efficiency (LE) - current density (J) characteristics and the current density (J) - bias (V) luminance (L) characteristics are shown in Figure 4b and c. The control device, without the solvent treatment, exhibits a performance comparable to other DBT-based devices with the same device structure.22, 37-38 Spin-coating of n-C12H26 only slightly improves the injected current density, which could be attributed to the slight decrease in the thickness (Figure 4c). As a result,


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the LEmax of the solvent-treated control device is slightly lower than that of the control device without the solvent treatment as shown in Table 1.

Figure 4. a) Schematic diagram of the device structure with the energy level of each layer. The red dashed line in PPF-SO15-DBT1 represents the energy level of the DBT units. The energy


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levels of PPF-SO15-DBT1 and G0 were derived from the cyclic voltammogram (Fig. S1) b) LEJ, c) J-V-L and d) EL spectra characteristics of the respective devices.

Table 1. The performance of the devices. Vona

LEmax

EQEmax Lmax

[V]

[cd/A]

[%]

[cd/m2] [x, y]

PPF-SO15-DBT1

5.4

1.02

1.11

2628

(0.632,0.350)

PPF-SO15-DBT1 rinsed by n-C12H26

5.0

0.88

0.94

2514

(0.635,0.349)

PPF-SO15-DBT1/G0

3.6

3.76

4.03

6187

(0.629,0.350)

Device

a

Von is defined as the voltage at which a luminance of 1 cd/m2 is reached.

b

CIE color coordinates are measured at J = 20 mA/cm2.

CIEb

In comparison to the control device, the device performance is significantly improved with the G0 ETL. As summarized in Table 1, the turn-on voltage (Von, voltage at 1 cd/m2) is reduced to 3.6 V from 5.4 V. The luminous efficiency increases to 3.76 cd/A from 1.02 cd/A. The peak luminance reaches 6187 cd/m2, more than double that of the control device. The shift in the emission spectrum can give rise to a higher luminance and a higher luminous efficiency. As shown in Figure 4d, the electroluminescence (EL) spectra of devices with and without the G0 ETL are identical, suggesting that the LE increase is due to the enhancement of the external quantum efficiency (EQE). As shown in Table 1, the EQE increases to 4.03% from 1.11% with the addition of the G0 ETL. The EQE improvement could be the result of better exciton confinement, improved exciton energy transfer and better charge carrier balance.


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It is clear from the device structure (Figure 4a) that not only does the G0 ETL layer physically separate the light emission layer from the metal cathode but also its relatively large Eg can prevent the excitons of PPF-SO15-DBT1 from being quenched by the metal cathode.39 As shown in Figure S2, as the thickness of G0 increases, the efficiency increases, verifying that the G0 ETL moves the recombination zone away from the cathode. Moreover, no EL emission from G0 is observed (Figure 4d), implying that the recombination zone is completely in the PPF-SO15DBT1 layer and the excitons of G0 migrate to the lower Eg conjugated polymer via either Förster or Dexter energy transfer at the heterojunction of PPF-SO15-DBT1/G0. As illustrated in Figure S3, there is large overlap between the G0 emission and the PPF-SO15-DBT1 absorption. In addition, the current density of the device with the G0 ETL is significantly higher than that of the device without the G0 ETL (Figure 4c). Because the anodes of the devices are exactly the same, the difference in the current density is attributed to the electron current Je. It is proposed that the G0 ETL facilitates the electron transport toward the emission layer, which leads to more balanced charge carriers, thereby improving the quantum efficiency. To verify the enhancement of the electron current, electron dominant devices were examined. Electron dominant devices. Electron dominant devices were fabricated with the configuration of ITO/Al/PPF-SO15-DBT1 (35 or 70 nm)/G0 (35 or 0 nm)/Ba/Al. The Je-V characteristics are shown in Figure 5. Without the solvent treatment or the G0 ETL, the device shows a rather low electron current. After the solvent treatment, the electron current only increases negligibly due to the slightly decrease in the thickness, consistent with the light emitting devices’ performance. For the devices with the G0 ETL, the electron current increases substantially. The increase in the electron current can be attributed to better electron injection and/or better electron transport by using the G0 ETL to replace part of the EML.


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Figure 5. The Je-V characteristics of the electron dominant devices. The device structure is ITO/Al/Organic layer/Ba/Al. As illustrated in Figure 4a, PPF-SO15-DBT1 has a deeper LUMO than that of G0, which means that if the cathode’s work function matches G0’s LUMO, it would also match the LUMO of PPF-SO15-DBT1. The work function of the Ba/Al cathode matches the LUMO of both G0 and PPF-SO15-DBT1, which induces energy level pinning.18, 40-41 As a result, the main mechanism for the increase in the electron current is the improved electron transport obtained by replacing part of the EML with the G0 ETL. As detailed in the S.I., the electron mobility of G0 is approximately 5.1 × 10-7 cm2 V-1 s-1, which is six orders of magnitude larger than the electron mobility of approximately 1.1 × 10-13 cm2 V-1 s-1 for PPF-SO15-DBT1. In other studies, red OLEDs based on the DBT derivative molecules usually suffer from the same problem of poor


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electron transport. The device performance was drastically improved only after thermally evaporating an ETL, such as 1,3,5-tris(N-phenylbenzimidizol-2-yl)-benzene (TPBi), tris(8hydroxyquinoline) aluminum (Alq3) or 2,9-dimethyl-4,7-diphenyl-1,10-phenan-throline (BCP), in vacuum.20, 22, 37, 42-43 CONCLUSIONS In summary, a novel semi-orthogonal solubility relationship in PLEDs has been developed and demonstrated. The alkane solvent is shown to be mild enough to be processed on top of the conjugated polymer film. For the first time, the alkane-soluble dendrimer G0 is applied as the ETL in PLEDs to enhance the device performance. With the G0 ETL, the maximum luminous efficiency and the external quantum efficiency of the PPF-SO15-DBT1 device more than triple. The turn-on voltage decreases from 5.4 V to 3.6 V. The enhancement of the device performance is attributed to better exciton confinement, improved exciton energy transfer and better charge carrier balance. The G0 ETL prevents the exciton from going close to the cathode, which reduces the exciton quenching by the cathode. Moreover, the exciton (if any) created in the ETL layer is completely transferred to the light emission layer. In addition, the G0 ETL facilitates electron transport, making the charge carriers more balanced, thereby improving the device performance. It should be noted that the alkane solution-processed ETLs are not in competition with the more popular water/alcohol solution-processed ETLs. In fact, they are also orthogonal to each other. As a result, more exquisite multilayer devices can be fabricated by combining the alkane with water/alcohol solution-processed ETLs. ASSOCIATED CONTENT


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Supporting Information. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org. The cyclic voltammogram measurements of PPF-SO15-DBT1 and G0. The overlap of G0’s EL and PPF-SO15-DBT1’s absorption, and performance of devices with different thicknesses of G0 ETL. The electron mobility calculation of PPF-SO15-DBT1 and G0.

AUTHOR INFORMATION Corresponding Author *Corresponding author’s E-mail address: [email protected] *Tel.: +86 20 87114346. Fax: +86 20 87110606. E-mail: [email protected]. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We are deeply grateful to the Ministry of Science and Technology (973 Program 2015CB655000), National Nature Science Foundation of China (51573056, 51373057), and Integration of Production and Research Projects of Guangdong Province (2014B090916001, 2015B090915001) for their financial supports.


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REFERENCES (1) Diao, Y.; Shaw, L.; Bao, Z.; Mannsfeld, S. C. B. Morphology Control Strategies for Solution-Processed Organic Semiconductor Thin Films. Energy Environ. Sci. 2014, 7, 21452159. (2) Etxebarria, I.; Ajuria, J.; Pacios, R. Solution-Processable Polymeric Solar Cells: A Review on Materials, Strategies and Cell Architectures to Overcome 10%. Org. Electron. 2015, 19, 34-60. (3) Liao, C.; Zhang, M.; Yao, M. Y.; Hua, T.; Li, L.; Yan, F. Flexible Organic Electronics in Biology: Materials and Devices. Adv. Mater. 2015, 27, 7493-7527. (4) Ying, L.; Ho, C. L.; Wu, H.; Cao, Y.; Wong, W. Y. White Polymer Light-Emitting Devices for Solid-State Lighting: Materials, Devices, and Recent Progress. Adv. Mater. 2014, 26, 24592473. (5) Zheng, H.; Zheng, Y.; Liu, N.; Ai, N.; Wang, Q.; Wu, S.; Zhou, J.; Hu, D.; Yu, S.; Han, S.; Xu, W.; Luo, C.; Meng, Y.; Jiang, Z.; Chen, Y.; Li, D.; Huang, F.; Wang, J.; Peng, J.; Cao, Y. All-Solution Processed Polymer Light-Emitting Diode Displays. Nat. Commun. 2013, 4, 1971-11971-7. (6) Jiang, Z.; Zhong, Z.; Xue, S.; Zhou, Y.; Meng, Y.; Hu, Z.; Ai, N.; Wang, J.; Wang, L.; Peng, J.; Ma, Y.; Pei, J.; Wang, J.; Cao, Y. Highly Efficient, Solution Processed Electrofluorescent Small Molecule White Organic Light-Emitting Diodes With a Hybrid Electron Injection Layer. ACS Appl. Mater. Interfaces 2014, 6, 8345-8352. (7) Jiang, C.; Liu, H.; Liu, B.; Zhong, Z.; Zou, J.; Wang, J.; Wang, L.; Peng, J.; Cao, Y. Improved Performance of Inverted Quantum Dots Light Emitting Devices by Introducing Double Hole Transport Layers. Org. Electron. 2016, 31, 82-89.


16

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(8) Huang, F.; Cheng, Y.-J.; Zhang, Y.; Liu, M. S.; Jen, A. K. Y. Crosslinkable HoleTransporting Materials For Solution Processed Polymer Light-Emitting Diodes. J. Mater. Chem. 2008, 18, 4495-4509. (9) Huang, F.; Wu, H.; Cao, Y. Water/Alcohol Soluble Conjugated Polymers as Highly Efficient Electron Transporting/Injection Layer in Optoelectronic Devices. Chem. Soc. Rev. 2010, 39, 2500-2521. (10) Duan, C.; Zhang, K.; Zhong, C.; Huang, F.; Cao, Y. Recent Advances in Water/AlcoholSoluble Pi-Conjugated Materials: New Materials and Growing Applications in Solar Cells. Chem. Soc. Rev. 2013, 42, 9071-9104. (11) Zhong, C.; Liu, S.; Huang, F.; Wu, H.; Cao, Y. Highly Efficient Electron Injection from Indium Tin Oxide/Cross-Linkable Amino-Functionalized Polyfluorene Interface in Inverted Organic Light Emitting Devices. Chem. Mater. 2011, 23, 4870-4876. (12) Liu, S.; Zhang, K.; Lu, J.; Zhang, J.; Yip, H. L.; Huang, F.; Cao, Y. High-Efficiency Polymer Solar Cells via The Incorporation of an Amino-Functionalized Conjugated Metallopolymer as a Cathode Interlayer. J. Am. Chem. Soc. 2013, 135, 15326-15329. (13) Gu, C.; Fei, T.; Yao, L.; Lv, Y.; Lu, D.; Ma, Y. Multilayer Polymer Stacking by In Situ Electrochemical Polymerization for Color-Stable White Electroluminescence. Adv. Mater. 2011, 23, 527-530. (14) Aizawa, N.; Pu, Y.-J.; Chiba, T.; Kawata, S.; Sasabe, H.; Kido, J. Instant Low-Temperature Cross-Linking

of

Poly(N-vinylcarbazole)

for

Solution-Processed

Multilayer

Blue

Phosphorescent Organic Light-Emitting Devices. Adv. Mater. 2014, 26, 7543-7546.


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(15) Gather, M. C.; Köhnen, A.; Falcou, A.; Becker, H.; Meerholz, K. Solution-Processed FullColor Polymer Organic Light-Emitting Diode Displays Fabricated by Direct Photolithography. Adv. Funct. Mater. 2007, 17, 191-200. (16) Köhnen, A.; Riegel, N.; Kremer, J. H. W. M.; Lademann, H.; Müller, D. C.; Meerholz, K. The Simple Way to Solution-Processed Multilayer OLEDs - Layered Block-Copolymer Networks by Living Cationic Polymerization. Adv. Mater. 2009, 21, 879-884. (17) He, Z.; Wu, H.; Cao, Y. Recent Advances in Polymer Solar Cells: Realization of High Device Performance by Incorporating Water/Alcohol-Soluble Conjugated Polymers as Electrode Buffer Layer. Adv. Mater. 2014, 26, 1006-1024. (18) Wang, L.; Jiang, Y.; Luo, J.; Zhou, Y.; Zhou, J.; Wang, J.; Pei, J.; Cao, Y. Highly Efficient and Color-Stable Deep-Blue Organic Light-Emitting Diodes Based on a Solution-Processible Dendrimer. Adv. Mater. 2009, 21, 4854-4858. (19) Li, Y.; Wu, H.; Lam, C.-S.; Chen, Z.; Wu, H.; Wong, W.-Y.; Cao, Y. Highly Efficient Blue and All-Phosphorescent White Polymer Light-Emitting Devices Based on Polyfluorene Host. Org. Electron. 2013, 14, 1909-1915. (20) Yu, L.; Liu, J.; Hu, S.; He, R.; Yang, W.; Wu, H.; Peng, J.; Xia, R.; Bradley, D. D. C. Red, Green, and Blue Light-Emitting Polyfluorenes Containing a Dibenzothiophene-S,S-Dioxide Unit and Efficient High-Color-Rendering-Index White-Light-Emitting Diodes Made Therefrom. Adv. Funct. Mater. 2013, 23, 4366-4376. (21) Zhong, Z.; Hu, Z.; Jiang, Z.; Wang, J.; Chen, Y.; Song, C.; Han, S.; Huang, F.; Peng, J.; Wang, J.; Cao, Y. Hole-Trapping Effect of the Aliphatic-Amine Based Electron Injection Materials in the Operation of OLEDs to Facilitate the Electron Injection. Adv. Electron. Mater. 2015, 1, 1400014-1-1400014-6.


18

Page 19 of 22

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


(22) Hou, Q.; Xu, Y.; Yang, W.; Yuan, M.; Peng, J.; Cao, Y. Novel Red-Emitting FluoreneBased Copolymers. J. Mater. Chem. 2002, 12, 2887-2892. (23) Liu, J.; Zou, J.; Yang, W.; Wu, H.; Li, C.; Zhang, B.; Peng, J.; Cao, Y. Highly Efficient and Spectrally Stable Blue-Light-Emitting Polyfluorenes Containing a Dibenzothiophene-S,Sdioxide Unit. Chem. Mater. 2008, 20, 4499-4506. (24) Aguirre, J. C.; Hawks, S. A.; Ferreira, A. S.; Yee, P.; Subramaniyan, S.; Jenekhe, S. A.; Tolbert, S. H.; Schwartz, B. J. Sequential Processing for Organic Photovoltaics: Design Rules for Morphology Control by Tailored Semi-Orthogonal Solvent Blends. Adv. Energy Mater. 2015, 5, DOI: 10.1002/aenm.201402020. (25) Xie, L.; Yoon, S.; Cho, Y. J.; Kim, K. Effective Protection of Sequential Solution-Processed Polymer/Fullerene Bilayer Solar Cell Against Charge Recombination and Degradation. Org. Electron. 2015, 25, 212-218. (26) Ying, L.; Hsu, B. B.; Zhan, H.; Welch, G. C.; Zalar, P.; Perez, L. A.; Kramer, E. J.; Nguyen, T. Q.; Heeger, A. J.; Wong, W. Y.; Bazan, G. C. Regioregular Pyridal[2,1,3]thiadiazole PiConjugated Copolymers. J. Am. Chem. Soc. 2011, 133, 18538-18541. (27) Lei, T.; Dou, J. H.; Cao, X. Y.; Wang, J. Y.; Pei, J. A BDOPV-Based Donor-Acceptor Polymer for High-Performance N-Type and Oxygen-Doped Ambipolar Field-Effect Transistors. Adv. Mater. 2013, 25, 6589-6593. (28) Wang, X.-Y.; Zhuang, F.-D.; Wang, J.-Y.; Pei, J. Incorporation of Polycyclic Azaborine Compounds into Polythiophene-Type Conjugated Polymers for Organic Field-Effect Transistors. Chem. Commun. 2015, 51, 17532-17535.


19


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 20 of 22

(29) Zhou, X.; Ai, N.; Guo, Z.-H.; Zhuang, F.-D.; Jiang, Y.-S.; Wang, J.-Y.; Pei, J. Balanced Ambipolar Organic Thin-Film Transistors Operated under Ambient Conditions: Role of the Donor Moiety in BDOPV-Based Conjugated Copolymers. Chem. Mater. 2015, 27, 1815-1820. (30) Jiang, Y.; Wang, J.-Y.; Ma, Y.; Cui, Y.-X.; Zhou, Q.-F.; Pei, J. Large Rigid Blue-Emitting π-Conjugated Stilbenoid-Based Dendrimers: Synthesis and Properties. Org. Lett. 2006, 8, 42874290. (31) Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Electron Transport Materials for Organic Light-Emitting Diodes. Chem. Mater. 2004, 16, 4556-4573. (32) Zhang, Y.; Huang, F.; Chi, Y.; Jen, A. K. Y. Highly Efficient White Polymer LightEmitting Diodes Based on Nanometer-Scale Control of the Electron Injection Layer Morphology through Solvent Processing. Adv. Mater. 2008, 20, 1565-1570. (33) An, D.; Zou, J.; Wu, H.; Peng, J.; Yang, W.; Cao, Y. White Emission Polymer LightEmitting Devices with Efficient Electron Injection From Alcohol/Water-Soluble Polymer/Al Bilayer Cathode. Org. Electron. 2009, 10, 299-304. (34) Wang, Q.; Zhou, Y.; Zheng, H.; Shi, J.; Li, C.; Su, C. Q.; Wang, L.; Luo, C.; Hu, D.; Pei, J.; Wang, J.; Peng, J.; Cao, Y. Modifying Organic/Metal Interface via Solvent Treatment to Improve Electron Injection in Organic Light Emitting Diodes. Org. Electron. 2011, 12, 18581863. (35) Song, Q.; Song, C.; Zhong, Z.; Hu, Z.; Wang, L.; Wang, J.; Cao, Y. Ether Solvent Treatment to Improve the Device Performance of the Organic Light Emitting Diodes with Aluminum Cathode. Org. Electron. 2015, 24, 241-245.


20

Page 21 of 22

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) Song, C.; Zhong, Z.; Hu, Z.; Wang, J.; Wang, L.; Ying, L.; Wang, J.; Cao, Y. Methanol Treatment on Low-Conductive PEDOT:PSS to Enhance the PLED's Performance. Org. Electron. 2016, 28, 252-256. (37) Hou, Q.; Zhou, Q.; Zhang, Y.; Yang, W.; Yang, R.; Cao, Y. Synthesis and Electroluminescent Properties of High-Efficiency Saturated Red Emitter Based on Copolymers from Fluorene and 4,7-Di(4-hexylthien-2-yl)-2,1,3-benzothiadiazole. Macromolecules 2004, 37, 6299-6305. (38) Huang, J.; Liu, Q.; Zou, J.-H.; Zhu, X.-H.; Li, A.-Y.; Li, J.-W.; Wu, S.; Peng, J.; Cao, Y.; Xia, R.; Bradley, D. D. C.; Roncali, J. Electroluminescence and Laser Emission of Soluble Pure Red Fluorescent Molecular Glasses Based on Dithienylbenzothiadiazole. Adv. Funct. Mater. 2009, 19, 2978-2986. (39) Cao, Y.; Parker, I. D.; Yu, G.; Zhang, C.; Heeger, A. J. Improved Quantum Efficiency for Electroluminescence in Semiconducting Polymers. Nature 1999, 397, 414-417. (40) Braun, S.; Salaneck, W. R.; Fahlman, M. Energy-Level Alignment at Organic/Metal and Organic/Organic Interfaces. Adv. Mater. 2009, 21, 1450-1472. (41) Hu, Z.; Zhong, Z.; Chen, Y.; Sun, C.; Huang, F.; Peng, J.; Wang, J.; Cao, Y. Energy-Level Alignment at the Organic/Electrode Interface in Organic Optoelectronic Devices. Adv. Funct. Mater. 2016, 26, 129-136. (42) Huang, J.; Qiao, X.; Xia, Y.; Zhu, X.; Ma, D.; Cao, Y.; Roncali, J. A Dithienylbenzothiadiazole Pure Red Molecular Emitter with Electron Transport and Exciton Self-Confinement for Nondoped Organic Red-Light-Emitting Diodes. Adv. Mater. 2008, 41724175.


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Page 22 of 22

(43) Thangthong, A.; Prachumrak, N.; Sudyoadsuk, T.; Namuangruk, S.; Keawin, T.; Jungsuttiwong, S.; Kungwan, N.; Promarak, V. Multi-Triphenylamine–Functionalized Dithienylbenzothiadiazoles as Hole-transporting Non-Doped Red Emitters for Efficient Simple Solution Processed Pure Red Organic Light-Emitting Diodes. Org. Electron. 2015, 21, 117-125.

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An Alkane-Soluble Dendrimer as Electron-Transport Layer in Polymer

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