1 research outputs found
Polyethylenimine Insulativity-Dominant Charge-Injection Balance for Highly Efficient Inverted Quantum Dot Light-Emitting Diodes
Quantum
dot (QD) light-emitting diodes (QLEDs) with an inverted
architecture suffer from charge-injection imbalance and severe QD
charging, which degrade device performance. Blocking excess electron
injection into QDs is crucial for efficient inverted QLEDs. It is
observed that polyethylenimine (PEI) has two opposite effects on electron
injection: one is blocking electron injection by its intrinsic insulativity
and the other one is promoting electron injection by reducing the
work function of ZnO/PEI. In this work, the insulating nature of PEI
has been dominantly utilized to reduce electron injection and the
charge-injection balance is realized when PEI becomes thicker and
blocks more excess electrons. Furthermore, PEI contributes to QD charging
suppression and results in a smoother surface morphology than that
of ZnO nanoparticles, which is beneficial for leakage current reduction
and QD deposition. As a result, the optimized QLED with 15 nm PEI
shows a 2.5 times improved efficiency compared to that of the QLED
without PEI. Also, the QLED possesses the maximum external quantum
efficiency and current efficiency of 16.5% and 18.8 cd/A, respectively,
accompanied with a low efficiency roll-off of 15% at 1000 cd/m<sup>2</sup>, which is comparable to that of the reported inverted red
QLED with the highest efficiency