Inverted polymer/quantum-dots hybrid white light emitting diodes

Highlights: • Efficient blue polymer doped with quantum dots is used as the emitting layer. • Polyetherimide is introduced to reduce the electron injection barrier. • White spectra of electroluminescence is stable. • This device shows a peak luminous efficiency of 5.3 cd/A. -- Abstract: Inverted polymer/quantum-dots (QDs) hybrid white light emitting diodes with high efficiency and color stability were fabricated. The white devices show high luminous efficiency of 5.3 cd/A, external quantum efficiency of 3.0%, by using polyetherimide (PEI) to modify zinc oxide layer as the electron injection layer and blue emitting polymer of poly (dibenzothiophene-S,S-dioxide-co-9,9-dioctyl-2,7-fluorene) (PFSO) doped with green and red quantum-dots (G-QDs, R-QDs) as the emitting layer. Pure white emission at Commission Internationale de L'Eclairage coordinates of (0.31, 0.32) was achieved by adjusting weight ratio of PFSO: G-QDs: R-QDs to be 10.0: 3.6: 2.2. In addition, the electroluminescence (EL) spectra of the white device are quite stable in the wide brightness range between 1.0 × 10² cd/m² and 1.0 × 10⁴ cd/m². The possible reason was that the PEI could reduce the energy barrier height between the cathode and emitting layer, and facilitate electron injection into the emitting layer. It's confirmed that both Forest energy transfer and charge trapping mechanisms work in the EL process and the latter is dominant.