Ting Gong, Yang Yang, Tongtong Xuan, Wenhao Bai, Haorui Dong, Tianliang Zhou, Rong-Jun Xie
First published: 30 May 2024
Laser & Photonics Reviews
DOI:10.1002/lpor.202301097
Abstract
Quantum dot (QD) color conversion films (QD-CCFs) are used in ultrahigh definition (UHD) Mini-LED backlit displays due to their narrow band emission and high color purity. However, their poor light conversion efficiency (LCE) leads to greater film thickness and thus high cost. Herein, this study proposes a local light field control strategy to enhance the LCE of QD-CCFs using high-refractive BN nanosheets. The LCEs of the green and red QD-CCFs can increase from 29.9% and 34.8% to 67.4% and 91.0% after adding BN nanosheets, respectively. Combining the experimental data with the finite-difference time domain (FDTD) simulations, the enhanced LCEs can be attributed to observably increased blue light absorption and improved light extraction efficiency of the light emitted from QDs. The white Mini-LEDs, prepared by integrating the optimized QD-CCFs containing BN nanosheets with blue Mini-LED chips, show a high luminous efficiency of 70.2 lm W−1, a high external quantum efficiency of 36.2%, and a wide color gamut of 96.3% Rec. 2020 standards. This work provides an interesting idea for designing high-efficiency QD-CCFs toward low-cost UHD Mini-LED backlit displays.
ABOUT ARTICAL
In today’s world of information overload, ultra-high-definition display technology has become a crucial area for those seeking exceptional visual experiences. Mini-LED backlit displays, known for their outstanding performance and cost balance, have earned their place in the high-end electronics market. Despite the numerous advantages of Mini-LED backlighting, it still faces the challenge of relatively high costs, which significantly restricts its broader commercial adoption.
Quantum Dot Color Conversion Films (QD-CCFs), as one of the core materials for Mini-LED backlit displays, play a crucial role in the overall performance of these displays. They directly impact key parameters such as thickness, brightness, contrast, color gamut, and cost. Traditional QD-CCFs suffer from a significant limitation: their relatively low light conversion efficiency (LCE). This not only hinders the further enhancement of brightness but also results in high manufacturing costs, which acts as a bottleneck for the development of Mini-LED backlit displays.
Previously, researchers have made numerous efforts to improve the photoluminescence performance of quantum dots. However, an important factor was overlooked—the impact of the internal light field distribution within QD-CCFs on light conversion efficiency.
Breakthrough in QD-CCFs: Localized Light Field Regulation Using Boron Nitride (BN) Nanosheets
A team led by Professor Xie Rongjun from Xiamen University addressed this issue by proposing a localized light field regulation strategy. They introduced high-refractive-index boron nitride (BN) nanosheets into QD-CCFs to improve light conversion efficiency. This significant improvement has provided powerful support for the optimization of Mini-LED backlight display performance. The results were published in Laser Photonics Review (DOI: 10.1002/lpor.202301097).
Through a series of experiments, the research team found that by introducing BN nanosheets with an average size of 300 nm into the composite film, the internal fluorescence quantum yield (IQY), blue light absorption (ABS), and external fluorescence quantum yield (EQY) of the QD-CCFs were significantly improved. This means more blue light could be effectively captured and utilized, rather than being lost as it had in previous designs.
Using Finite-Difference Time-Domain (FDTD) simulation, the researchers further revealed the underlying mechanism: after the introduction of BN nanosheets, the blue light field distribution was significantly enhanced. More blue light photons were confined within the thin film, greatly improving blue light absorption efficiency. Meanwhile, the interaction between BN nanosheets and PMMA formed an optical microcavity, generating a waveguide effect. This served as an efficient pathway for light propagation, significantly enhancing the light extraction efficiency of quantum dot emission.
Promising Future for Mini-LED with Optimized QD-CCFs
The research team successfully fabricated white Mini-LEDs by combining the optimized QD-CCFs containing BN nanosheets with blue Mini-LED chips. These white Mini-LEDs exhibited exceptional performance, with a luminous efficiency of 70.2 lm/W, an external quantum efficiency (EQE) of 36.2%, and a color gamut that covered 96.3% of the Rec. 2020 standard. The color reproduction was vivid and lifelike. Notably, the thickness of the QD-CCFs containing BN nanosheets was only 48 μm, significantly thinner than the traditional reference film, which had a thickness of 180 μm. This reduction not only significantly improved display performance but also drastically lowered production costs, providing a new and efficient approach for low-cost ultra-high-definition Mini-LED backlight displays.
This groundbreaking work received funding from the National Key R&D Program (2022YFB3503800, 2022YFB3503801), the National Natural Science Foundation of China (U2005212, 12374385, 52172157), the Guangdong Provincial Foundation for Basic and Applied Research (2023A1515030004), and the Shenzhen Science and Technology Program (JCYJ20230807091404009).
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