DOI: 10.5176/2251-189X_SEES18.41
Authors: Wei-Li Hong, Yu-Chiang Chao
Abstract: In this study, we propose high-performance lead-free perovskite infrared LEDs based on low-temperature solution-processed CsSnI3 perovskite. Two methods, one-pot solution synthesis method and toluene dripping method were employed to prepare the CsSnI3 films. The CsSnI3 films synthesized via the one-pot solution synthesis method exhibit a sponge-like morphology. The infrared LEDs fabricated using such spongelike CsSnI3 films exhibit poor performance. Contrarily, the CsSnI3 films prepared via the toluene dripping method exhibit compact micrometer-sized CsSnI3 grains with very few pinholes and cracks at the grain boundaries. Based on time-resolved photoluminescence measurement, the PL lifetime of the CsSnI3 film is in femtosecond region. Infrared LEDs fabricated with such high-quality CsSnI3 films exhibit high device performance. Electroluminescence at 950 nm was obtained with maximum radiance of 40 W sr−1 m−2 at a current density of 364.3 mA/cm2 and maximum EQE of 3.8{6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} at 4.5 V, respectively. Distributions of the peak EQEs of devices indicate the reproducibility of our devices. Based on impedance spectroscopy analysis, the recombination resistance of the device fabricated by one-pot solution synthesis method is lower than the one of the device fabricated by the toluene dripping method for about one order of magnitude, which implies an increase of the recombination rate in the device fabricated by one-pot solution synthesis method. Since the radiance of the device fabricated by one-pot solution synthesis method is inferior to the one of the device fabricated by the toluene dripping method, it can be concluded that the superior performance of the device fabricated by the toluene dripping method is attributed to its lower non-radiative recombination. Furthermore, the trap density of state (tDOS) in CsSnI3 films prepared by both methods can be derived from the angular frequency dependent capacitance. The tDOS in the device fabricated by one-pot solution synthesis method is higher than the one of the device fabricated by the toluene dripping method, which explains the inferior performance of the device fabricated by one-pot solution synthesis method. These high-performance and lead-free infrared LEDs are suitable for infrared lighting, optical communications, and noninvasive biomedical imaging.
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