Efficient inverted organic light-emitting devices using a charge-generation unit as electron-injection layers

Abstract Efficient electron injection from cathode to electron transport layer is generally required to realize high-performance inverted organic light-emitting devices (IOLEDs). In this work, highly efficient IOLEDs are developed by employing a non-doped charge-generation unit of 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN)/Al/LiF as electron-injection layers (EILs). The ultraviolet photoelectron spectroscopy (UPS) shows that the insertion of HAT-CN layer reduces the work function of EILs by 0.21 eV. Combined with the current-voltage characteristics of electron-only devices, the role of the HAT-CN layer in promoting electron injection is confirmed. What's more, the double EILs device with Rubrene as a probe verifies the strong hole blocking ability of HAT-CN/Al/LiF. Based on the EILs, the inverted blue phosphorescent OLEDs with a maximum current efficiency of 29.4 cd/A are realized. The excellent performance proves the superiority of HAT-CN/Al/LiF as EILs.