Deciphering the Causes of the Rapid Electroluminescence Loss in Blue Quantum Dot Light‐Emitting Devices

Abstract Electroluminescence (EL) loss mechanisms in quantum dot light‐emitting devices (QLEDs), especially blue (B) emitting ones, remain unclear. Here, it is identified that – aside from some partially reversible deterioration in the photoluminescence quantum yield (PLQY) of the quantum dots‐emissive layer (QDs‐EML) – the rapid EL loss in B‐QLEDs is caused mainly by an increase in electron leakage‐across the hole transport layer (HTL) and a subsequent damage to the hole injection layer (HIL), resulting in a deterioration in hole supply to the QDs EML. EL and PL measurements on devices with marking layers (MLs) placed in different locations uncover that electron supply to the QDs‐EML is easier than hole supply in B‐QLEDs in general, causing the electron (e)/hole (h) to be >1 and significant electron leakage to the HIL, even in fresh devices. Under electrical stress, this electron leakage increases further, causing the charge imbalance in the QDs‐EML to deteriorate further and more electrons to reach the HIL. The selective peel‐off‐and‐rebuilt experiment verifies the HIL changes and the role of electrons in inducing them. Modified devices with reduced electron supply show 30X longer EL lifetime, proving the role of excess electrons in the rapid EL loss in B‐QLEDs.