采用硫氰酸铵添加剂的高效天蓝色钙钛矿发光二极管

High-efficiency sky blue perovskite light-emitting diodes with ammonium thiocyanate additive

金属卤化物钙钛矿发光器件具有可溶液加工、高发光效率和良好色纯度等诸多优良特性,受到了广泛的关注,但蓝色钙钛矿发光器件发光效率和光谱稳定性等方面的问题限制了钙钛矿材料在照明和显示领域的进一步发展.本工作研究硫氰酸铵添加剂对准二维混合卤化物钙钛矿薄膜形貌、结晶度、光物理和电致发光特性的影响.结果表明硫氰酸铵能有效钝化准二维混合卤化物钙钛矿薄膜的缺陷,提高结晶度,调节相分布,从而改善其电荷传输特性和发光效率.硫氰酸铵浓度为20%的准二维钙钛矿发光二极管的发光峰值波长位于486 nm处,器件的最大外量子效率为5.83%,最大亮度为1258 cd/m^(2),分别比未添加硫氰酸铵的器件提升了6.7倍和3.6倍,同时器件发光光谱稳定性和驱动稳定性也得到了明显的提升.本研究为提高蓝色准二维混合卤化物钙钛矿发光二极管的特性提供了一种简单有效的方法.

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(NH_(4)SCN)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(NH_(4)SCN)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%-NH_(4)SCN sample is 1.7 times higher than that of the control sample,which is attributed to the defect passivation effect of NH_(4)SCN probably due to the Lewis acid-base interaction with Pb2+.Meanwhile,the hole mobility of the 20%-NH_(4)SCN sample is measured to be 1.31×10^(–5) cm^(2)/(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%-NH_(4)SCN possesses an EL maximum at 486 nm and a maximum external quantum efficiency(EQE)of 5.83%and a luminance of 1258 cd/m^(2),which are 6.7 and 3.6 times higher than those of the control device without NH_(4)SCN,respectively.At the same time,the EL spectra of the 20%-NH_(4)SCN 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 NH_(4)SCN addition inhibits halide phase separation and improves the EL spectrum stability.In addition,the T50 operational life-time of the 20%-NH_(4)SCN 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 NH_(4)SCN-modified sample.This research provides a simple and effective method to improve the performances of quasi-two-dimensional mixed-halide perovskite blue-emitting diodes.