Record high external quantum efficiency of 20% achieved in fully solution-processed quantum dot light-emitting diodes...

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely used as a hole injection material in quantum dot (QD) light-emitting diodes (QLEDs). However, it degrades the organic materials and electrodes in QLEDs due to its strong hydroscopicity and acidity. Although hole-conductive metal oxides have a great potential to solve this disadvantage, it is still a challenge to achieve efficient and stable QLEDs by using these solution-processed metal oxides. Herein, the state-of-the-art QLEDs fabricated by using hole-conductive MoO_x QDs are achieved. The α-phase MoO_x QDs exhibit a monodispersed size distribution with clear and regular crystal lattices, corresponding to high-quality nanocrystals. Meanwhile, the MoO_x film owns an excellent transmittance, suitable valence band, good morphology and impressive hole-conductivity, demonstrating that the MoO_x film could be used as a hole injection layer in QLEDs. Moreover, the rigid and flexible red QLEDs made by MoO_x exhibit peak external quantum efficiencies of over 20%, representing a new record for the hole-conductive metal oxide based QLEDs. Most importantly, the MoO_x QDs afford their QLEDs with a longer T₉₅ lifetime than these devices made by PEDOT:PSS. As a result, we believe that the MoO_x QDs could be used as efficient and stable hole injection materials used in QLEDs.