Accelerated response speed of quantum-dot light-emitting diodes by hole-trap-induced excitation memory

Abstract

Fast-response electroluminescent devices are crucial for optoelectronic applications that involve high-speed operations. Quantum-dot light-emitting diodes are solution-processed electroluminescent devices with high efficiencies and stabilities, and they are of potential use in such applications. However, their response speed is typically limited by slow charge injection and transport across the organic hole-transport layers. We show that the transient electroluminescent responses of quantum-dot light-emitting diodes are influenced by their excitation history in pulsed operations. As the pulse interval decreases, this results in an increased response speed and the emergence of another fast-response electroluminescent channel, indicating the presence of excitation-memory effects. We show that these dynamics are due to deep-level hole traps in the organic hole-transport layers with fast charge-trapping and slow charge-detrapping characteristics. We develop a low-capacitance micro-quantum-dot light-emitting diode that exploits the excitation-memory-induced fast-response channel. The device, which has a −3 dB bandwidth of up to 19 MHz, exhibits an electroluminescent modulation frequency of 100 MHz and data-transmission rates of up to 120 Mbps with sub-picojoule energy consumption.