Improving the performance of phosphorescent polymer light-emitting diodes using morphology-stable carbazole-based iridium complexes

Abstract

A series of morphology-stable carbazole-based iridium(III) complexes with green to red emission have been prepared and characterized by elemental analysis, nuclear magnetic resonance, and mass spectroscopy. Their thermal, electrochemical, electronic absorption, and photoluminescent properties have been studied. Highly efficient polymer light-emitting devices by using these complexes as dopant emitters, both non-conjugated polymer (PVK) and conjugated polymer, polyhedral oligomeric silsesquioxane-terminated poly(9,9-dioctylfluorene) [PFO(poss)], as the host materials, have been achieved. With the device structure of ITO/PEDOT/(PFO(poss) + 30% PBD)–2 wt.% 1/Ba/Al, a maximum external quantum efficiency of 6.4% and a maximum luminous efficiency of 6.00 cd A⁻¹ with red emission at 608 nm were obtained. With the device configuration of ITO/PEDOT/(PFO(poss) + 30% PBD)–4 wt.% 4/Ba/Al, a maximum external quantum efficiency of 9.9% and a maximum luminous efficiency of 22.4 cd A⁻¹ with yellow–green emission at 544 nm were realized. The increased morphology stability of 1 and 2 imparted by the N-decyl long chains at the N atom of carbazole results in significantly better device performance than their short chain analogues 1a and 2a under identical device configurations.