Towards a full-color display of perovskite LEDs

Metal halide perovskite (MHP) materials have many advantages such as wide color gamut, high luminous efficiency and low synthesis cost. Since the first room-temperature emission perovskite light-emitting diode (PeLED) was reported in 2014, the performance parameters of PeLED have improved rapidly in a few years. The external quantum efficiency (EQE) of green, red and near-infrared emission PeLEDs has exceeded 20%, and the EQE of blue PeLEDs has exceeded 17%. Recently, multiple scientific research teams have achieved PeLED with more than 10,000 hours of operational stability, eliminating concerns about the intrinsic instability of perovskite materials. The performance indicators of PeLED continue to approach the most advanced organic and quantum dot LEDs, and show unique advantages in color purity, material cost and other aspects. PeLED thus stands out in the field of wide color gamut display, attracting widespread attention from academia and industry.

Despite the amazing progress, PeLEDs still have some challenges in enabling commercial display applications. On the one hand, high-performance PeLEDs only operate in a small area of active area. When the active area is expanded, the high inhomogeneity of the large-area film becomes a major obstacle. On the other hand, most research on PeLEDs has focused on prototype devices with a single emitting pixel. The high-resolution, full-color MHP array patterning strategy and device integration technology are relatively lagging, which strongly hinders the commercialization of PeLED displays. In addition, high-performance PeLEDs are mainly based on rigid substrates, thus limiting their potential application scenarios. MHP materials have solution-processable properties and intrinsic mechanical flexibility, which provides prospects for the preparation of MHP-based flexible optoelectronic devices.

In view of this, the research team of Yuan Mingjian of Nankai University published a review article entitled “Perovskite light-emitting diodes toward commercial full-colour displays: progress and key technical obstacles” in Light: Advanced Manufacturing.

In this review, the authors discuss the key technical bottlenecks of PeLEDs in commercial display applications. Including the preparation of large-area PeLEDs, the patterning strategy of PeLEDs, and flexible PeLED devices. The authors review the technical roadmap to achieve these goals, highlight current challenges, and look ahead to these MHP materials and PeLED devices to accelerate PeLED devices into the consumer electronics market.

Large area PeLED

Large-scale manufacturing of PeLEDs is of great significance for display panels. However, high-performance PeLED devices demonstrated in lab-scale production typically have only a few square millimeters of emission area. When the emission area is expanded, the crystallinity and uniformity of the MHP film decrease, resulting in low device performance. These shortcomings make it challenging for PeLEDs to extend their excellent electroluminescent (EL) properties to large-scale production lines. In order to achieve large-area and high-quality production of devices, it is necessary to develop a feasible large-area MHP thin film deposition technology. It includes the improvement of existing spin coating methods and the use of deposition techniques compatible with large-scale coating, such as novel scraping or vapor deposition methods.

Figure 1. Large-area perovskite thin film deposition strategy based on spin coating (a), scraping (b) and vapor deposition (c); Large area PeLED devices based on spin coating (d), scraping (e), and vapor deposition (f). Source: Light: Advanced Manufacturing 4, 15 (2023)

Patterning strategy for PeLEDs

Micro- or nanopixel arrays and their fabrication methods are critical to the development of advanced integrated optoelectronic platforms. Accurate and highly integrated arrays are prerequisites for incorporating these emerging MHP materials into full-color high-resolution displays. Researchers have made great efforts to develop structured MHPs and have demonstrated MHP optical films with unique optoelectronic properties in lasers, metasurfaces, and nonlinear optical devices. However, the integration of patterned MHP films into full-color, high-resolution electroluminescent devices remains a serious challenge. Developing high-performance patterned PeLEDs requires compatibility with existing device manufacturing processes and unification of high optical performance and low electrical losses. In this section, the authors focus on MHP array patterning attempts applied to high-resolution LED devices. These strategies include mask-assisted lithography, maskless inkjet printing methods, nanoimprinting, and transfer techniques.

Figure 2. top-down (a) and bottom-up (b) lithography steps for patterned perovskite arrays; Nanoimprint (C) and imprint-transfer (D) steps for patterned perovskite arrays. Source: Light: Advanced Manufacturing 4, 15 (2023)

Flexible PeLED

Flexible LED devices show great application potential in areas such as portable, wearable displays, and biomedical imaging. In this section, the author briefly introduces the research progress of flexible PeLED. The authors review the mechanical property adjustment strategies of MHP emitting layers in flexible and stretchable equipment, and illustrate the relationship between structural optimization and photoelectric properties of materials. The authors introduce electrode materials compatible with flexible PeLEDs, such as structured metals, conductive polymers, low-dimensional carbon materials, and their composites. They also propose comprehensive strategies to improve the performance parameters of these candidate materials, such as flexibility, conductivity, and light transmittance. The authors also discuss interface and energy level engineering to improve the compatibility of these electrodes with MHP-active layers. (Source: Advanced Manufacturing WeChat public account)

Figure 3. Typical application scenarios of flexible stretchable LED devices (a); Young’s modulus of perovskite materials in different crystal plane directions (b); Several typical flexible electrodes. Source: Light: Advanced Manufacturing 4, 15 (2023)

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