Conjugated Zwitterionic Polyelectrolytes and Their Neutral Precursor as Electron Injection Layer for High‐Performance Polymer Light‐Emitting Diodes

Abstract

Conjugated polyelectrolytes (CPEs) have attracted considerable attention in recent years due to their signifi cant application potential in organic optoelectronic devices [1][2][3][4] and chemo-/ bio-sensors. [ 5 , 6 ] Their pendant ionic groups offer them unique solubility in high polarity solvents, which is orthogonal to most of the commonly used conjugated polymer active materials, and allow the fabrication of solution-processed multilayer devices to maximize the performance. Moreover, it was proved that the CPE's pendant polar groups also can effectively improve electron injection from high work-function metals (such as Al, Ag, Au), which open a way to achieve all printable roll-to-roll polymer based organic electronic devices and the fi rst fully solution processed polymer light-emitting diodes (PLEDs) have been realized based on them. [ 7 ] Despite their application potential in devices, most of CPE contain mobile counter-ions, which can migrate into the emission layer (EML) and may affect the longterm stability of devices. [ 8 ] In addition, the response time of the devices and the mobility of the CPE are also greatly infl uenced by the nature of their counter-ions. [ 9 , 10 ] To overcome these, one alternative way is to develop water/alcohol soluble conjugated polymers with neutral high polarity pendant groups. [ 11 ] However, it is very challenging to get highly water/alcohol soluble neutral conjugated polymers due to that conjugated polymers always contain a very rigid, highly hydrophobic main chain and the polarity of nonionic pendant groups is usually not high enough to ensure them good solubility in water/alcohol. Zwitterionic polyelectrolytes contain both anionic and cationic groups, which usually exhibit good water/alcohol solubility and there is no mobile counter-ions among them. [ 12 ] Moreover, recent research has shown that zwitterionic groups can also enhance the electron injection from high work-function metal cathodes as those traditional ionic groups (such as ammonium) or other high polarity groups (such as amino, diethanol amino etc.) [ 13 ] Thus, conjugated zwitterionic polyelectrolytes (CZPEs) could be the promising candidate as electron transporting/injecting layer (ETL) for PLEDs, combining the advantages of good charge transporting ability, mobile ions free nature and good water/alcohol solubility, etc. Although there are rarely researches reported on the using of CZPEs for organic electronic devices.Herein, we report the development of a new CZPE, poly[9,9-bis((N-(3-sulfonate-1-propyl)-N,N-diethylammonium)-hexyl)-2,7-fl uorene] (PF 6 NSO), with different quaternized degrees and their precursor poly[9,9-bis(6-(N,N-diethylamino)-hexyl)fl uorene] (PF 6 N) as highly effi cient electron injecting/ transporting materials for PLEDs. Our results show that the zwitterionic groups among PF 6 NSO not only enhance the alcohol solubility of the polymers, but also signifi cantly enhance their electron injection ability, which are promising candidates of new interface modifi cation layer for orga...

Structures and Synthesis of Zwitterionic Polymers

“…On the other hand, a large number of novel building blocks as well as polymer structures have evolved recently, too. This concerns to a lesser degree the nature of the zwitterionic moieties incorporated into the polymer, but mostly the nature of the polymer skeleton, including electronically conjugated ones [96][97][98][99][100][101][102][103][104][105], as well as the overall polymer architecture.…”

Conjugated zwitterionic polyelectrolyte-based interface modification materials for high performance polymer optoelectronic devices

“…Moreover, solution-processed multilayer devices, which are critical for a better device performance, can be easily realized by depositing different layers with orthogonal solvents. For examples, many types of highly polar pendant groups (such as cationic, 8,14,42,43 anionic, 44,45 zwitterionic 34,46,47 and neutral highly polar pendant groups 14,18,32,[48][49][50][51][52] ) and conjugated main chain building blocks (such as uorene, 8,14,18,34,[42][43][44][45][46][47][48][49][50][51] carbazole, 30,52 triphenylamine, 32,53,54 thiophene 23,27,33 etc.) 3,5,[14][15][16] In polymer light-emitting diodes (PLEDs), WSCPs can greatly enhance the electron injection from high work-function metal cathodes, which in turn leads to the realization of high-efficiency all-printable PLEDs.…”

Hyperbranched red light-emitting phosphorescent polymers based on iridium complex as the core

“…The measurements were carried out in an inert atmosphere by using the ITO-coated glass as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode as the reference electrode. The ferrocene/ferrocenium (Fc/Fc + ) redox couple was used as the standard, which has a potential of -4.8 eV relative to vacuum [26]. that the E HOMO of copolymers is essentially not sensitive to the molar ratio of iridium complex.…”