Ultrathin (∼10 nm) insulating polymer films are
commonly
employed as an interfacial modification layer (IML) to improve charge
balance and suppress interfacial exciton quenching in quantum dot
light-emitting diodes (QLEDs). However, because the thickness is smaller
than the energy transfer distance, interfacial exciton quenching is
only partially suppressed, leading to the degrading of device performance.
In this work, a thick (35 nm) inorganic CdS film is developed to serve
as the IML of CdSe quantum-dot-based QLED. Benefiting from relatively
low electron mobility and well-matched energy level, the CdS IML can
effectively improve charge balance. In addition, because the thickness
is larger than the energy transfer distance, interfacial exciton
quenching can be completely blocked. As a result, the QLEDs with CdS
IML exhibit a maximum EQE of 21.2% and a peak current efficiency of
24.2 cd A–1, which are about 1.32- and 1.4-fold
higher than 16.1% and 17.3 cd A–1 of the devices
without CdS IML, respectively. Our work offers an efficient method
to completely block interfacial exciton quenching, which may open
a new avenue for developing higher-performance QLEDs.