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.

Enhanced efficiency in polymer solar cells by incorporation of phenothiazine-based conjugated polymer electrolytes

“…The LUMO energy levels of CPEs estimated from the HOMO energy level and the optical band gap were 2.12 and 2.22 eV, respectively, which were quite different from the LUMO energy level of PCBM (3.88 eV). Even though there is a mismatch of the LUMO energy levels between the CPEs and PCBM, the electron collection/transporting ability from the photoactive layer to the cathode will be improved because of the formation of interface dipoles by the thin layer of CPEs at the cathode interface, which reduces the work function of the Al cathode [12][13][14]26,27]. Details will be presented following section.…”

“…A thin layer of LiF (ca. 1 nm) is well known as interfacial material [9,10], solution processible interlayer materials such as polyethylene oxide [11], neutral conjugated polymers with polar side chains [12], non-conjugated polyelectrolytes [13][14][15][16], and conjugated polyelectrolytes (CPEs) [17][18][19][20][21][22] have been also applied for interfacial layer in PSCs. These materials enable the fabrication of the devices without damaging the under-layer.…”

Enhancing the performance of polymer light-emitting diode via methanol treatment

“…Because most of the conjugated polymers show similar solubility, leading to damage to the underling layers during new layer casting. One of the effective options is to use non-mixing solvent between the functional and emissive layers [6][7][8][9][10][11]. Since most emissive polymers are soluble only in nonpolar-solvent, functional layers are usually fabricated from polar-solvent solution, such as alcohols.…”

“…To achieve highly efficient light-emitting, multilayered structures were commonly used with the addition of electron injection/transport or hole injection/transport layers [6][7][8][9][10][11][12][13]. However, unlike small molecular devices, where multi-layer structures with well-defined individual layers can be fabricated using vacuum deposition methods, it is a big challenge to fabricate multilayered PLEDs.…”

Ring Walking/Oxidative Addition Reactions for the Controlled Synthesis of Conjugated Polymers

“…35 Signals due to the methylene protons from the pendant oligo(ethylene glycol) chains appear between 3.6 and 2.6 ppm 36 and the singlet attributed to the trimethylsilyl-protected ethynyl group appears at 0.28 ppm. 37 These data are consistent with the structure of the product 12 in Scheme 4.…”