Efficient white polymer light-emitting diodes from single polymer exciplex electroluminescence

Abstract

Efficient white polymer light-emitting diodes were developed based on exciplex electroluminescence from a single polymer PFTS that consists of an electron-donating side chain and an electron-withdrawing backbone. It is noted that the device performances can be dramatically improved by incorporating a certain amount of high triplet energy level poly(9-vinylcarbazole) (PVK) into the emissive layer, which can lead to a more balanced charge carrier and decrease the exciton back transfer from the formed exciplex to the backbone of poly(fluorene-co-dibenzothiophene-5,5-dioxide). The luminous efficiency can be further improved by utilizing PVK as the hole transport layer, which can achieve greenish white emission with a luminous efficiency of 9.12 cd A⁻¹ and CIE coordinates of (0.25, 0.37). Of particular interest is that the emission of PFTS can be modified by varying the thickness of the emissive layer by virtue of micro-cavity effects, where the optimized device exhibits a remarkable luminous efficiency of 7.37 cd A⁻¹ with CIE coordinates of (0.30, 0.43). These observations demonstrated the great promise of utilizing the single polymer with the exciplex emission for the construction of efficient white polymer light-emitting devices.