Efficient, blue light-emitting diodes using cross-linked layers of polymeric arylamine and fluorene

Single-, double- and triple-layer polymer light-emitting diodes (PLEDs) with indium-tin oxide (ITO) anodes and Ca cathodes were fabricated, based on solution processable and thermally cross-linkable hole transporting polyarylamine and blue luminescent polyfluorene; and an electron transporting oxadiazole trimer. Triple-layer PLEDs show the highest efficiency, brightness and saturation of blue emission. These results are interpreted in terms of charge injection balance and electron-hole recombination efficiency. The maximum external quantum efficiencies achieved (>1%) are comparable to the best polymer blue PLEDs.