Unraveling the Turn-On Limitation of Quantum-Dot Electroluminescence via a Stepwise-Increasing Voltage Measurement

Whether the electroluminescence turn-on of quantum-dot light-emitting diodes (QLEDs) is determined by electrons or holes has long been controversial. Given that the charge-carrier trapping or/and capturing processes affect the current measured through an organic semiconductor film, then the long-lived trap information can be extracted by measuring the current through the film with a periodic stepwise-increasing voltage. We develop easy-to-operate technology to detect the long-lifetime traps in the organic small-molecule materials and demonstrate that the turn-on behavior of the QLEDs is determined by the hole injection. Moreover, it is verified that the long-lived hole traps are also responsible for the luminance overshoot behavior for the device driven by a constant current. We believe this characterization technology can provide a significant platform to deeply understand the properties of both materials and photoelectronic devices.