Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 11474232)
Received Date:02 June 2021
Accepted Date:14 July 2021
Available Online:16 August 2021
Published Online:05 October 2021
Abstract:Metal halide perovskite light-emitting diodes have attracted much attention due to their excellent characteristics such as low-cost solution-processing, high luminous efficiency and excellent color purity. However, low luminous efficiency and spectrum stability of blue perovskite light-emitting device restrict the further development of perovskite materials in the field of displays and lighting. Here in this work, we study the effects of ammonium thiocyanate (NH4SCN) addition on the morphology, crystal structure, photo-physics, charge transport and electroluminescence properties of quasi-two-dimensional mixed-halide perovskite films by measuring scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Vis spectrum, steady-state photoluminescence (PL), and transient PL and analyzing the current density–voltage characteristics of hole-dominated device and current density-voltage-luminance plots of light-emitting device. The results indicate that ammonium thiocyanate (NH4SCN) can effectively passivate the defects, improve the crystallinity, and modulate the phase distribution of quasi-two-dimensional mixed-halide perovskite film, thereby increasing charge transport and luminescent efficiency. Notably, PL intensity of the 20%-NH4SCN sample is 1.7 times higher than that of the control sample, which is attributed to the defect passivation effect of NH4SCN probably due to the Lewis acid-base interaction with Pb2+. Meanwhile, the hole mobility of the 20%-NH4SCN sample is measured to be 1.31 × 10–5 cm2/(V·s), which is much higher than that of the control sample (3.58 × 10–6 cm2/(V·s)). As a result, sky-blue quasi-two-dimensional mixed-halide perovskite light-emitting diode with 20%-NH4SCN possesses an EL maximum at 486 nm and a maximum external quantum efficiency (EQE) of 5.83% and a luminance of 1258 cd/m2, which are 6.7 and 3.6 times higher than those of the control device without NH4SCN, respectively. At the same time, the EL spectra of the 20%-NH4SCN device are barely changed under different operating voltages, whereas the EL spectra of the control device show a 7–10 nm red-shift under the same condition, indicating that the NH4SCN addition inhibits halide phase separation and improves the EL spectrum stability. In addition, the T50 operational life-time of the 20%-NH4SCN device is measured to be about 110 s, which is superior to that of the control device (39 s) due to improved film quality of NH4SCN-modified sample. This research provides a simple and effective method to improve the performances of quasi-two-dimensional mixed-halide perovskite blue-emitting diodes. Keywords:quasi-two-dimensional mixed-halide perovskites/ blue-emitting diodes/ ammonium thiocyanate/ defect passivation
表1不同NH4SCN浓度钙钛矿薄膜的时间分辨光致发光的拟合参数总结 Table1.Summarization of the fitting parameters for TRPL decay traces of the perovskite films with different NH4SCN concentrations.
图 5 (a) 不同NH4SCN浓度器件的归一化电致发光光谱; (b) 在不同电压下0% NH4SCN和 (c) 20% NH4SCN器件电致发光光谱, 插图给出20% NH4SCN器件的照片; (d) 在起始亮度为100 cd/m2下器件工作寿命特性 Figure5. (a) Normalized electroluminescence spectra of the devices with different NH4SCN concentrations; (b) normalized electroluminescence spectra of the 0% NH4SCN and (c) 20% NH4SCN devices under different operating voltages, the inset shows a photograph of a working 20% NH4SCN device; (d) operational life-time properties of the devices measured with an initial luminance of 100 cd/m2.