Using an environmentally stable metal as the cathode in a polymer light-emitting diode (PLED) is an essential requirement for its practical application. We present the preparation of a water/alcohol soluble copoly(p-phenylene) (P1) containing pendant azacrown ether and ethylene glycol ether groups as a highly efficient electron injection layer (EIL) for PLEDs, allowing the use of environmentally stable aluminum as the cathode. Multilayer PLEDs [ITO/PEDOT:PSS/PF-Green-B/EIL/Al] using P1 as EIL exhibit significantly enhanced device performance, particularly in the presence of K2CO3 or Cs2CO3. The maximum luminous power efficiency and maximum luminance of the device with Cs2CO3-doped P1 as EIL were enhanced to 9.16 lm W(-1) and 17,050 cd m(-2), respectively, compared with those without EIL (0.16 lm W(-1), 890 cd m(-2)). The turn-on voltage was also significantly reduced from 5.7 V to 3.7 V simultaneously. The performance enhancement has been attributed to improved electron injection which has been confirmed by the rise in open-circuit voltage (Voc) obtained from photovoltaic measurements. The incorporation of such an electron injection layer significantly enhances device performance for PLEDs with an environmentally stable metal as the cathode.
To enhance electroluminescence of polymer light-emitting diodes (PLEDs) using an environmentally stable aluminum cathode, we designed a novel water/alcohol-soluble electron injection material, FTC, composed of a fluorene core and triple azacrown ether terminals. FTC significantly enhances the emission performance of PLEDs [ITO/PEDOT:PSS/EML/EIL/Al] when used as the electron injection layer (EIL), especially in the presence of metal carbonates and metal acetates. The metal carbonate-doped devices showed the best performance due to their higher dissociation rate than metal acetates. In particular, the device using K 2 CO 3 doped-FTC as the electron injection layer (EIL) exhibited significantly enhanced performance compared to the device without an EIL. For the device based on PF-Green-B as the emitting layer, the performance was significantly enhanced to 17 460 cd m À2 , 21.58 cd A À1 , and 12.42 lm W À1 , respectively, from 1220 cd m À2 , 0.72 cd A À1 , and 0.27 lm W À1 for the non-FTC device. Using HY-PPV as the emitting layer, the device performance was also significantly enhanced to 10 990 cd m À2 , 6.93 cd A À1 , and 5.27 lm W À1 , respectively, from 680 cd m À2 , 0.07 cd A À1 , and 0.03 lm W À1 for the non-EIL device. The results indicate that FTC with metal cations is an excellent electron injection candidate for the performance enhancement of PLEDs with a high work function Al cathode. † Electronic supplementary information (ESI) available: Synthesis and characterization of monomers, the 1 H NMR spectra, and thermal, optical, electrochemical and optoelectronic properties of FTC, and the proposed chemical structure of doped-FTC. See
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