Electron‐Rich Alcohol‐Soluble Neutral Conjugated Polymers as Highly Efficient Electron‐Injecting Materials for Polymer Light‐Emitting Diodes

Abstract

We report the design and synthesis of three alcohol‐soluble neutral conjugated polymers, poly[9,9‐bis(2‐(2‐(2‐diethanolaminoethoxy) ethoxy)ethyl)fluorene] (PF‐OH), poly[9,9‐bis(2‐(2‐(2‐diethanol‐aminoethoxy)ethoxy)ethyl)fluorene‐alt‐4,4′‐phenylether] (PFPE‐OH) and poly[9,9‐bis(2‐(2‐(2‐diethanolaminoethoxy) ethoxy)ethyl)fluorene‐alt‐benzothiadizole] (PFBT‐OH) with different conjugation length and electron affinity as highly efficient electron injecting and transporting materials for polymer light‐emitting diodes (PLEDs). The unique solubility of these polymers in polar solvents renders them as good candidates for multilayer solution processed PLEDs. Both the fluorescent and phosphorescent PLEDs based on these polymers as electron injecting/transporting layer (ETL) were fabricated. It is interesting to find that electron‐deficient polymer (PFBT‐OH) shows very poor electron‐injecting ability compared to polymers with electron‐rich main chain (PF‐OH and PFPE‐OH). This phenomenon is quite different from that obtained from conventional electron‐injecting materials. Moreover, when these polymers were used in the phosphorescent PLEDs, the performance of the devices is highly dependent on the processing conditions of these polymers. The devices with ETL processed from water/methanol mixed solvent showed much better device performance than the devices processed with methanol as solvent. It was found that the erosion of the phosphorescent emission layer could be greatly suppressed by using water/methanol mixed solvent for processing the polymer ETL. The electronic properties of the ETL could also be influenced by the processing conditions. This offers a new avenue to improve the performance of phosphorescent PLEDs through manipulating the processing conditions of these conjugated polymer ETLs.

Nonconjugated Anionic Polyelectrolyte as an Interfacial Layer for the Organic Optoelectronic Devices

“…0.1 eV). This is a different result from the cases of the reported IFLs based on PEO, CPEs, − P-OH, and PVs, , for which the large increase of V oc was attributed to the enhancement of the PCE of the devices. Recently, Wang et al reported a similar observation in the device with poly­(vinyl­pyrroli­done) (PVP) as an IFL, which is a nonconjugated neutral polymer with a strong dipole moment.…”

“…Most of the increase in the device efficiency resulted from the 12% enhancement in the short-circuit current ( J sc ), while the fill factor (FF) was very close to that of the device without an IFL. This result is not usually observed in the previously reported results of the buffer layer based on PEO, CPEs, − P-OH, and PVs, , for which either the J sc and the FF increase simultaneously or only the FF increases along with the increase of the V oc .…”

High Efficiency Inverted Organic Solar Cells with a Neutral Fulleropyrrolidine Electron-Collecting Interlayer

“…The bare ITO was largely hydrophilic with a water contact angle of ∼28°. Different from most diethanolamino-functionalized conjugated macromolecules with amphiphilic properties reported in previous literature, , the resulting diethanolamino-functionalized fullerene derivative FPNOH presented a hydrophobic surface with a water contact angle of ∼95°, which could be attributed to the strong hydrophobic fullerene components.…”

Water/alcohol soluble conjugated polymers as highly efficient electron transporting/injection layer in optoelectronic devices

“…9). 93 Similar results were also observed among the phosphorescent devices, where the devices with P36 and P37 exhibited excellent performances and P38 did not work as an ETL. Photovoltaic studies showed that both P36/Al and P37/Al cathode device exhibited a larger V oc of 2.1 V and 2.2 V, respectively, than those of the Al (1.1 V) and Ba/Al (1.8 V) cathode devices, while the P38/Al cathode device showed a much smaller V oc (1.3 V), indicating no reduction of the electron injection barrier from Al cathode by inserting P38 layer.…”