Lead-free Perovskite for Ultraviolet micro- LEDs based White-Light Communication

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Lead-free Perovskite for Ultraviolet micro- LEDs based White-Light Communication

Item Type Conference Paper

Authors Lu, Hang;Alkhazragi, Omar;Hasanov, Bashir;Naphade,

Rounak;Ng, Tien Khee;Bakr, Osman;Mohammed, Omar F.;Ooi, Boon S.

Citation Lu, H., Alkhazragi, O., Hasanov, B., Naphade, R., Ng, T. K., Bakr, O. M., Mohammed, O. F., & Ooi, B. S. (2022). Lead-free Perovskite for Ultraviolet micro-LEDs based White-Light Communication.

2022 IEEE Photonics Conference (IPC). https://doi.org/10.1109/

ipc53466.2022.9975631 Eprint version Post-print

DOI 10.1109/ipc53466.2022.9975631

Publisher IEEE

Rights This is an accepted manuscript version of a paper before final publisher editing and formatting. Archived with thanks to IEEE.

Download date 2023-12-15 21:35:30

Link to Item http://hdl.handle.net/10754/686454

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Lead-free Perovskite for Ultraviolet micro-LEDs based White-Light Communication

Hang Lu Photonics Laboratory

King Abdullah University of Science and Technology Thuwal 23955-6900, Saudi Arabia

[email protected] Omar Alkhazragi Photonics Laboratory

[email protected]

Bashir Hasanov

Division of Physical Science and Engineering King Abdullah University of Science and Technology

Thuwal 23955-6900, Saudi Arabia [email protected]

Rounak Naphade

Thuwal 23955-6900, Saudi Arabia [email protected] Tien Khee Ng

Photonics Laboratory

[email protected] Osman M. Bakr

Omar F. Mohammed

Boon S. Ooi Photonics Laboratory

[email protected]

Abstract—Despite growing interest in lead-halide perovskites for visible-light communication (VLC), the health concerns associated with lead hinder their widespread application. Herein, we demonstrate for the first time a lead-free perovskite phosphor-based VLC link using an ultraviolet-micro-LED, achieving 84.9 CRI, 4115-K CCT, and 1.5-Mb/s data rate.

Keywords—perovskite, phosphors, white light, visible-light communication I. INTRODUCTION

Indoor visible-light communication (VLC) can alleviate the congestion in the radio frequency spectrum while providing high-quality illumination. The white light in VLC systems is typically obtained from blue/violet light-emitting diodes (LEDs) chips and phosphors partially converting blue light into longer-wavelength colors spanning the visible light band. However, conventional phosphors used for white-light LEDs suffer from some shortcomings. For example, the widely used yttrium aluminum garnet (YAG) shows poor color rendering index (CRI) and high correlated color temperature (CCT) [1]. To overcome this problem, organic materials have been presented as potential candidates, but substantially degrade over time due to their intrinsic properties, especially under high- temperature use-scenarios [2]. Recently, lead-halide perovskites become promising for optoelectronic devices owing to their tunable bandgap and high photoluminescence quantum yield (PLQY) [3]. However, their main drawbacks, which include the toxicity of lead and material instability, need to be resolved [4]. It is therefore critical to explore new safe and efficient alternative phosphors that are suitable for VLC and other color-converting applications. Herein, we demonstrate a VLC link based on an organic-inorganic perovskite phosphor with a high absolute PLQY of near unity, and a wide spectral emission ranging from 500 to 700 nm under 365- nm ultraviolet (UV) micro-LED excitation, which can provide a CRI of 84.9 and 4115-K CCT when combined with a blue LED.

Despite the long photoluminescence (PL) lifetime of the used perovskite material, which is in the order of μs, a net data rate of 1.5 Mb/s was achieved using orthogonal frequency-division multiplexing (OFDM) with adaptive bit and power loading to take advantage of the exceptionally high PLQY to improve the data throughput using higher modulation orders. Furthermore, through improvements to the nanostructure of the material and the use of excitation sources of a higher power, the data rate is expected to be even higher.

The lead-free nature of this material, along with its high conversion efficiency, makes it a promising alternative to conventional and toxic phosphors. As the first demonstration of VLC links using lead-free perovskite, this study paves the way for safer, more sustainable VLC systems.

II. MATERIAL AND UVMICRO-LEDCHARACTERIZATION

The PL and absorption spectra of the organic-inorganic perovskite are shown in Fig. 1(a). The phosphor can be excited by photons with wavelengths below 400 nm and produces yellow emission with peak intensity around 575 nm and a wide full width at half maximum (FWHM) of 101 nm. The broad yellow-emitting region exhibits its potential to mix with blue light to obtain high-quality

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white light for illumination. The wide nature of the spectrum is due to the exciton self-trapping, which also leads to the large Stokes shift (215 nm). In our experiments, an in-house 365-nm micro-UV-LED (100 μm×100 μm) is used as the excitation source in the VLC system [see Fig. 1(b)]. The LED was fabricated following a standard fabrication process. 5-nm Ni, 5-nm Au, and ~70-nm ITO layers were deposited on the p-GaN layer. The mesas are then formed using inductively coupled plasma reactive-ion etching (ICP- RIE) followed by sidewall isolation using a 200-nm SiO2 layer. Finally, n- and p-metal pads (Ti/Au) are deposited. The light-output–

current–voltage (L–I–V) plot is shown in Fig. 1(c).

III. ILLUMINATION AND COMMUNICATION PERFORMANCE

We perform an experiment to study the white light generated by utilizing the yellow-emitting phosphor as light converters excited by ultraviolet-micro-LEDs in addition to a blue LED (λ = 450 nm). Operating the UV LED at 153 mA (0.7-mW optical power), the system generates a high-quality white light (CCT = 4115 K) with a CRI of 84.9 which is suitable for indoor lighting. The VLC link was tested using the same LED injection current and an avalanche photodetector (APD) as the receiver. The light was focused on the active area of the APD using a 20× objective with no filters added. Figs. 2(b) and 2(c) show the bit- and power-loading details of the quadrature amplitude modulation (QAM) OFDM signal that was generated based on the estimated signal-to-noise ratio (SNR). A net data rate of 1.5 Mb/s is achieved with a bit error ratio (BER) of 1.1×10^-3, which is below the 7%-overhead forward error correction (FEC) BER limit (3.8×10^-3). The data rate can be significantly improved by using sources with higher optical power and by optimizing the nanostructure of the material to achieve the best balance between the white-light quality and the communication performance.

IV. CONCLUSION

In this work, we successfully demonstrated an illumination and communication system by using a new lead-free phosphor with a UV micro-LED. Because of the wide spectrum of the yellow light emitted from the phosphor (101-nm FWHM), a CRI of 84.9 was achieved at a CCT of 4115 K. Despite the characteristically long PL lifetime of the used tin-halide perovskite, a 1.5-Mb/s data rate was achieved through a spectrally efficient OFDM scheme, highlighting the potential of the lead-free perovskite as a safe alternative to conventional phosphors used in VLC systems.

REFERENCES

[1] Chen, Lung-Chien, et al. "Warm white light-emitting diodes using organic–inorganic halide perovskite materials coated YAG: Ce3+ phosphors." Ceramics International 44.4 (2018): 3868-3872.

[2] Park, Byung‐wook, and Sang Il Seok. "Intrinsic instability of inorganic–organic hybrid halide perovskite materials." Advanced Materials 31.20 (2019):

1805337.

[3] Akkerman, Quinten A., et al. "Tuning the optical properties of cesium lead halide perovskite nanocrystals by anion exchange reactions." Journal of the American Chemical Society 137.32 (2015): 10276-10281.

[4] Huang, Shouqiang, et al. "Postsynthesis Potassium‐Modification Method to Improve Stability of CsPbBr3 Perovskite Nanocrystals." Advanced Optical Materials 6.6 (2018): 1701106.

Fig. 2. (a) The spectrum of white light generated using a UV micro-LED, yellow-emitting lead-free perovskite phosphor and a commercial blue LED. Inset:

Generated white light in the CIE 1931 color space (chromaticity coordinates). (b) The maximum and used spectral efficiency for all subcarriers. Inset:

constellation diagrams. (c) SNR and power-loading factors.

(a) (b) (c)

Fig. 1. (a) Absorption (red), excitation (blue), and PL (black) spectra of the phosphor. (b) Representative micrograph of the used UV micro-LED and (c) L–I–

V plot of a 100 𝜇m × 100 𝜇m LED.

(a) (b) (c)