Dual hole transport layers for blue-light-emitting PLED: Suppress the formation of exciplex towards high device performance and color purity

Abstract

The realization of high-performance blue polymer light-emitting diodes typically requires a hole transport layer to facilitate hole injection, primarily due to the deep highest occupied molecular orbital (HOMO) energy levels of the blue light-emitting polymers. However, the widely-used hole transport layers (HTLs) are prone to induce exciplex with longer wavelength emission when cooperating with those n-type blue-light-emitting layers, due to the HOMO and lowest unoccupied molecular orbital (LUMO) energy levels offsets. To avoid formation of exciplex and improve device performance of blue light-emitting, we employed two hole-transport layers consisting of a cross-linkable poly(indenofluorene-co-triphenylamine) copolymer and an additional poly(9-vinylcarbazole) (PVK) layer. The devices with dual HTLs have an enhanced luminous efficiency of 7.67 cd A−1 while keep the electroluminescent spectrum identical to the device based on PVK devices. The resulting blue light-emitting device based on such two-layer HTL exhibited remarkable stability, with luminous efficiency remained about 6.6 cd A−1 at a luminance of 10000 cd m−2. Our results shown that the dual HTLs device structure is a promising strategy for constructing high performance solution-processed blue polymer light-emitting diodes.