Copolyphenylenes with pendant benzimidazolyl and diethanolaminohexyloxy groups: Synthesis and electron-transporting application in PLEDs

Two new electron-transporting copolyphenylenes P1NH and P2NH possessing balanced charges crucial to emission efficiency of polymer light-emitting diodes (PLEDs) have been synthesized and applied as an electron-transporting layer (ETL). The main chain structure is all para-linkage for P1NH and both para- and meta-linkage for P2NH, with the same pendant electron-withdrawing benzimidazolyl and polar diethanolaminohexyloxy groups. Both copolymers possess excellent thermal stability (T_d > 300 °C, T_g > 100 °C) due to their rigid backbones. In addition, the pendant groups effectively lower LUMO (∼ −2.70 eV) and HOMO (∼ −5.70 eV) levels, resulting in improved electron-transporting and hole-blocking capabilities. Multilayer yellow-emitting PLEDs with a configuration of ITO/PEDOT:PSS/SY/ETL/LiF/Al were successfully fabricated by the spin-coating process. The maximum luminance and maximum current efficiency of the P1NH-based device were 12,881 cd/m² and 10.94 cd/A, respectively, superior to the performance of P2NH-based device (4938 cd/m², 3.70 cd/A) and the device without ETL (8690 cd/m², 2.78 cd/A). Current results indicate that P1NH is highly effective in enhancing electron transport and device performance.