Solution-Processed Light-Emitting Diodes based on Non-Toxic Materials

YU-CHIANG CHAO^1*

¹Department of Physics, National Taiwan Normal University, Taipei, Taiwan

* Presenter:YU-CHIANG CHAO, email:ycchao@ntnu.edu.tw

Solution-Processed Light-Emitting Diodes based on Non-Toxic Materials
Yu-Chiang Chao*
Department of Physics, National Taiwan Normal University, Taipei, Taiwan
E-mail: ycchao@ntnu.edu.tw; yuchiangchao@gmail.com
Solution-processed optoelectronic devices are attractive because of the potential low-cost fabrication and the compatibility with flexible substrate. However, the utilization of toxic elements such as lead and cadmium in current optoelectronic devices raises environmental concerns. Here we demonstrate that non-toxic gold (Au) nanoclusters and lead-free cesium tin iodide (CsSnI3) can be used as the emissive material in the light-emitting diodes (LEDs).
For the application of Au nanoclusters, we demonstrate that white-light-emitting diodes can be achieved by utilizing non-toxic and environment-friendly Au nanoclusters. Yellow-light-emitting gold nanoclusters were blended with the blue-light-emitting organic host materials to form the emissive layer. A current efficiency of 0.13 cd/A was achieved. The Commission Internationale de l’Eclairage chromaticity coordinates of (0.27, 0.33) were obtained from our experimental analysis, which is quite close to the ideal pure white emission coordinates (0.33, 0.33).
As for the lead-free halide perovskite, including CsSnI3 and Cs2SnI6, LEDs based on both materials were realized. Cs2SnI6 can be easily obtained by oxidizing CsSnI3. Take CsSnI3 for example, the morphologies perovskite films fabricated using room temperature one-pot solution synthesis and toluene dripping methods were investigated. Under optimized conditions, the film prepared using room temperature one-pot solution synthesis method exhibits a sponge-like morphology, whereas that prepared using toluene dripping method shows compact micrometer-sized grains with few pinholes and cracks at the grain boundaries. Using the high-quality CsSnI3 film prepared via the toluene dripping method, we fabricated an LED with electroluminescence (EL) at 950 nm. The device exhibits maximum radiance of 40 W sr−1 m−2 at a current density of 364.3 mA/cm2 and maximum external quantum efficiency (EQE) of 3.8% at 4.5 V. This study proposes infrared LEDs without any toxic elements for infrared lighting, optical communications, and noninvasive biomedical imaging. The Cs2Sn(IxBr1-x)6 is also used for LEDs and will be discussed in detail.
References
1. Y. C. Chao, K. P. Cheng, C. Y. Lin, Y. L. Chang, Y. Y. Ko, T. Y. Hou, C. Y. Huang, W. H. Chang and C. A. J. Lin, Scientific Reports, 2018, 8, 8860.
2. W. L. Hong, Y. C. Huang, C. Y. Chang, Z. C. Zhang, H. R. Tsai, N. Y. Chang and Y. C. Chao, Adv. Mater., 2016, 28, 8029.

Keywords: perovskite, LEDs