Highly stable full-color display device with VLC application potential using semipolar μLEDs and all-inorganic encapsulated perovskite nanocrystal

The techniques of high-speed communication and high-resolution display kit are both essential to modern life, as they constitute the foundations of those attractive concepts: Internet of Things, virtual/augmented reality, and metverse. If they are expected to be integrated, being realized simultaneously in one single device in the form of visible light communication (VLC) and micro-LED (μLED) array, it will be thrilling that this new technique would combine the advantages of both, such as avoiding occupying the limited electromagnetic sources, confidentiality, energy saving, and large color gamut, etc.

 

So far, to combine communication and display remains in a concept, without any primitive prototype yet been invented. There are some drawbacks that hinder the realizations. First, the wavelength shift of μLED chips upon driving current. Second, the μLED display can only produce one color. If extended to the three primary colors that needed for display, it requires either massive transferring or incorporating with color conversion layers.

 

In current stage, by using fluorescent color conversion layers is a reliable way to realize full-colorization, due to the quick development of quantum dots (QDs). QDs are naturally adapted to the color conversion layer of display technique. The narrow width of emission spectra and low fluorescent lifetime indicate the potentials of large color gamut and high refresh rate, respectively.

 

Perovskite nanocrystal (PNCs), compared to the II-IV QDs, are superior in defect tolerance, color purity and cost reduction and can be an update to traditional QDs. However, The PNC is prone to the erosion in the ambient environment, in which the oxygen and water steam turn it into non-emissive phases. As consequence, the PNC requires robust shells as protection.

 

In this article, the Prof. Zhong Chen's group in Xiamen University and Prof Hao-Chung Kuo's group in National Yang Ming Chiao Tung University reports a promising approach for the development of effective full-color displays are to combine blue μLEDs with color conversion layers, as shown in Fig. 1. The stability of PNCs in ambient conditions and under exposure to blue light can be improved using a SiO2 coating, as shown in Fig. 2. Related results were published in Photonics Research Vol. 9, Issue 11, 2021 (Tingzhu Wu, Yue Lin, Yu-Ming Huang, et al. Highly stable full-color display device with VLC application potential using semipolar μLEDs and all-inorganic encapsulated perovskite nanocrystal[J]. Photonics Research, 2021, 9(11): 11002132).

 

Fig. 1 Highly stable full-color display device with VLC application potential using semipolar μLED and inorganic encapsulated perovskite nanocrystals

 

Fig. 2 SiO2 coating improves the stability of PNC under environmental conditions and light radiation conditions

 

This study proposes a device that could be used for both display and VLC applications. The semipolar blue μLED array fabricated in this study shows a negligible wavelength shift, indicating a significant reduction in the quantum confined Stark effect. Owing to its shorter carrier lifetime, the semipolar μLED array exhibits an impressive peak 3 dB bandwidth of 655 MHz and a data transmission rate of 1.2 Gb/s corresponding to an injection current of 200 mA, as shown in Fig. 3.

 

Fig. 3 Frequency response of PNC-μLED

 

The PNC–μLED device assembled from a semipolar μLED array with PNCs demonstrates high color stability and wide color-gamut features, achieving 127.23% and 95.00% of the National Television Standards Committee standard and Rec. 2020 on the CIE 1931 color diagram, respectively. These results suggest that the proposed PNC–μLED device is suitable for both display-related and VLC applications, as shown in Fig. 4.

 

Fig. 4 Color gamut and color shift of the PNC-μLED under different current densities.

 

"This work set a milestone for the application of μLED display with VLC", Prof. Chen comments, "In the future, electric devices tend to be highly integrated, as we have already witnessed so far. μLEDs should also follow this trend of being multi-functional, and this work revealed such possibility. Also, it has proven the competence of PNCs in the application end, as long one substantially enhances its reliability."

 

Currently, Zhong Chen's group and Hao-Chung Kuo's group are working on aspects for further improvement. Investigation on the full duplex VLC system with μLEDs; Exploration of the multiple communication channels on the red and green pixels.