Enhancing the Overall Performances of Blue Light-Emitting Electrochemical Cells by Using an Electron-Injecting/Transporting Ionic Additive.

Light-emitting electrochemical cells (LECs) have emerged as a promising emissive thin-film technology for next-generation solid-state lighting. However, blue LECs show low performances, which has remained a bottleneck for the fabrication of white LECs for lighting applications. Here, we demonstrate a remarkable enhancement of overall device performance for blue LECs by using an electron-injecting/transporting ionic additive, that is, [Zn(bpy)3 ](PF6 )2 (bpy is 2.2'-bipyridine, PF6 - is hexafluorophosphate). It is revealed that adding [Zn(bpy)3 ](PF6 )2 into the active layers of blue LECs accelerates the device response, simultaneously enhances the brightness and efficiency, reduces the efficiency roll-offs, significantly improves the blue color stability upon the continuous electrical operation, and enhances the device operational stability at optimized conditions. The remarkable enhancement of the overall device performance upon adding [Zn(bpy)3 ](PF6 )2 results from facilitated electron injection/transport and thus more balanced electron-hole recombination and more centered recombination zone, as well as the reduction of phosphorescence concentration quenching in the LECs. The work demonstrates for the first time that the use of electron-injecting/transporting ionic additives such as [Zn(bpy)3 ](PF6 )2 is a facile yet effective strategy to remarkably boost the overall performances of blue LECs.