Nb ₂ CT _x ‐MXene Nanosheets for Organic Light‐Emitting Diodes Achieving Extremely Outstanding Electroluminescence Performance and Stability

Abstract Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is widely used hole injection material in solution‐processed organic light‐emitting diodes (OLEDs), but its inherent strong acidity and hygroscopicity accelerate the deterioration of device performance. Herein, novel 2D MXene is proposed as a promising hole injection material. Specifically, Nb 2 CT x ‐MXene nanosheets with a main size distribution at 400–800 nm are synthesized by etching aluminum from Nb 2 AlC, followed by ultrasonic exfoliation. After further carrying out UV‐Ozone treatment, the work function of Nb 2 CT x nanosheets is adjusted to 5.05 eV, forming an ideal cascade hole injection when they are incorporated between the ITO anode and hole transport layer. Consequently, employing Nb 2 CT x ‐MXene nanosheet film as hole injection layer (HIL), a typical Ir(ppy) 3 ‐based green phosphorescent OLED exhibits a low turn‐on voltage of 2.9 V, and achieves an exceptional external quantum efficiency of 28.62%, which is among the highest values for corresponding devices with solution‐processed HIL reported in the literatures. A 25 × 20 mm 2 large size OLED with nanosheets HIL is also confirmed, realizing uniform light emission. Moreover, the proposed Nb 2 CT x ‐MXene nanosheets‐based device simultaneously displays extremely high stability, having a luminance decay of only 49.7% (50 h later), significantly superior to 91.2% of PEDOT:PSS‐based reference device, indicating a huge potential application.