UV-ozone treated Ti3C2Tx-MXene nanosheets as hole injection layer for organic light-emitting diodes

In this work, we successfully synthesized Ti3C2Tx-MXene nanosheets with a lateral dimension of 1 similar to 2 mu m by using wet-chemical etchant and sonication-assisted liquid-phase exfoliation method. After UV-ozone treatment, the work function for Ti3C2Tx-MXene nanosheets was adjusted to 5.14 eV well matching to indium tin oxide (ITO) anode (4.80 eV). Using Ti3C2Tx-MXene nanosheets as hole injection layer (HIL), Ir(ppy)(3)-based green organic light-emitting diodes (OLEDs) were fabricated, and the resulting devices exhibit a low turn-on voltage of 3.0 V and the high current efficiency, power efficiency and external quantum efficiency of 72.79 cd/A, 54.44 lm/W and 20.34 %, which are obviously better than these of 67.38 cd/A, 50.38 lm/W and 18.65 % for PEDOT:PSS-based reference device. Further, FIrpic- and Ir(pq)(2)acac-based blue and red OLEDs with Ti3C2Tx-MXene nanosheets HIL were demonstrated, which also show the significantly improved device efficiency of 44.56 cd/A, 32.44 lm/W and 22.07 % for blue device and 39.17 cd/A, 38.54 lm/W and 21.90 % for red device than these for corresponding PEDOT:PSS-based devices, proving the universal applicability of Ti3C2Tx-MXene nanosheets as HIL in OLEDs. The higher performance for Ti3C2Tx-MXene nanosheets-based devices can be attributed to the appropriate work function, high transmittance, high carrier mobility and good film forming property for Ti3C2Tx-MXene nanosheets. This is the first report about the MXene using as HIL in OLEDs, which opens up a new way to develop high-performance holes injection materials for solution-processed OLEDs.