Polyethylenimine modified sol-gel ZnO electron-transporting layers for quantum-dot light-emitting diodes

With the rapid development of quantum-dot light-emitting diodes (QLEDs), the efficiency and operational stability have not been the bottleneck limiting their commercialization. Consequently, functional layers/materials appropriate for low-cost and time-saving technologies is the next challenge to address. Here a polyethylenimine (PEI) modified smooth sol-gel zinc oxide (s-ZnO) electron-transporting layer is fabricated to replace the conventional ZnO nanoparticles. The PEI can not only improve the wettability of the s-ZnO surface, but also promote charge injection balance. Capacitance and transient electroluminescence spectrum measurements confirm that the charge accumulation within the PEI-containing device is reduced, hence suppressing non-radiative recombination. As a result, the maximum current efficiency and external quantum efficiency of QLED with PEI layer is 14.3 cd/A and 10.34%, respectively, 25% higher than that of n-ZnO ETL based device.