Title: Progress in the Development of Colloidal Quantum Well Light-Emitting Diodes
Abstract: Abstract: In recent years, colloidal quantum wells (CQWs), also known as semiconductor nanoplatelets, have become the new kind of promising optoelectronic material because of their excellent optoelectronic properties, such as high color purity, high photoluminescence quantum efficiency, and adjustable color emissions. As a significant application of CQWs, light-emitting diodes based on CQWs (or CQW-LEDs) possess a number of advantages, such as an extremely narrow spectrum, excellent color purity, high efficiency, solution-processed fabrication, and good compatibility with flexible electronics. CQW-LEDs demonstrate an important application prospect in the fields of next-generation display and solid-state lighting, and therefore, attract significant attention from academic and industrial settings. In this review, some basic concepts of CQW-LEDs are first introduced (e.g., the design of CQW materials, employment of device structures, and understanding of emission mechanisms), which are expected to help with understanding this new type of LEDs. Thereafter, from the perspective of CQW emitting material types, the recent research progress in the development of CQW-LEDs based on core-only CQWs, core/crown CQWs, core/shell CQWs, complex-heterojunction-based CQWs, and impurity-doped CQWs is presented. The properties of various CQWs are also compared. In this section, by combining the recent work from our research group, the design strategies of high-performance CQW-LEDs are discussed in detail, including the analyses of material selection, device structure, working mechanism, and luminescence process. In the next section, the integrated applications of CQWLEDs are illustrated, such as their use in LiFi-type communication, furthermore, their preparation as flexible optoelectronic materials is also reported. Finally, the present challenges (e.g., low efficiencies, short lifetimes, sub-optimal device engineering, and a narrow emission color region) and future development opportunities (e.g., flexible displays, flexible lighting, and CQW-LEDs with low-cost printing fabrication processes) of CQW-LEDs are discussed. Although the performance of CQW-LEDs still lags behind other kinds of state-of-the-art soft-material-based LEDs (e.g., organic LEDs, colloidal quantum dot LEDs, and perovskite LEDs), it has been gradually enhanced in the last eight years. Upon overcoming the current challenges, the prospect for the mass production of CQW-LEDs will be undoubtedly feasible. Thus, this review is not only an important reference that discusses the evolution of CQW-LEDs, it also provides insightful ideas for the development of materials for other optoelectronic applications (e.g., solar cells, lasers, photodetectors, sensors, Xray imaging, and light communication).