Emerging solution-processable light-emitting diodes for next-generation data communications

Abstract

Light-emitting diodes (LEDs) have emerged as a prospective contender that has gained substantial attention for data communications in recent years. This can be attributed to their advantageous characteristics, such as low cost, low power consumption and eye-safe properties. Additionally, high-speed LEDs are particularly attractive for Internet of Things (IoT) devices and also find important applications in photonic interconnects and biomedical sensors. Organic semiconductors, colloidal quantum dots (CQDs) and metal halide perovskites offer excellent optoelectronic properties, mechanical flexibility and solution processability, thus rendering them appealing materials for fast LEDs. Although the concept of improving modulation performance has been well understood in conventional III-V nitride light sources for years, research on LEDs made from these solution-processable materials is rarely undertaken. Hence, this dissertation explores the possibilities of deploying these solution-processable LEDs for data communications. We commence our investigation by employing two distinct fabrication methods, namely inkjet printing and spin-coating, to develop fast organic LEDs (OLEDs) based on a widely investigated conjugated polymer blend. Through the analysis of device performance, we rigorously evaluate the practicality of using these techniques to produce high-speed devices while also identifying and tackling the existing technological obstacles ahead. Regarding our exploration of QD-based LEDs (QLEDs), we demonstrate tactics to enhance the charge transport process of QDs and thereby inspect the impact of carrier mobility on determining device modulation bandwidth. As a result of an efficient ligand modification treatment, we see an approximate fivefold improvement in device bandwidth. Lastly, we shift the topic to perovskite LEDs (PeLEDs). Through rational compositional optimisation, we show perovskite emitters that exhibit superior luminescence properties and optimal photophysical dynamics. This progress, in conjunction with a meticulously engineered device architecture featuring a Fabry-Pérot microcavity, allows us to achieve modulation bandwidths of up to 42.6 MHz and data rates above 50 Mbps. By analysing the recombination behaviour of charged species across a spectrum of carrier density regimes, we elucidate the mechanism underlying the correlation between these photophysical characteristics and device modulation performance. Further analysis suggests that the intrinsic bandwidth may feasibly extend to gigahertz levels. This represents the first successful demonstration of high-speed perovskite light sources, potentially matching the performance of the existing mainstream devices. We believe this is a milestone for PeLEDs entering a new phase of their applications.