Work-function engineering of graphene anode by bis(trifluoromethanesulfonyl)amide doping for efficient polymer light-emitting diodes

Graphene has been considered to be a potential alternative transparent and flexible electrode for replacing commercially available indium tin oxide (ITO) anode. However, the relatively high sheet resistance and low work function of graphene compared with ITO limit the application of graphene as an anode for organic or polymer light-emitting diodes (OLEDs or PLEDs). Here, flexible PLEDs made by using bis(trifluoromethanesulfonyl)amide (TFSA, [CF₃SO ₂]₂NH) doped graphene anodes are demonstrated to have low sheet resistance and high work function. The graphene is easily doped with TFSA by means of a simple spin-coating process. After TFSA doping, the sheet resistance of the TFSA-doped five-layer graphene, with optical transmittance of ≈88%, is as low as ≈90 Ω sq^-1. The maximum current efficiency and power efficiency of the PLED fabricated on the TFSA-doped graphene anode are 9.6 cd A^-1 and 10.5 lm W^-1, respectively; these values are markedly higher than those of the PLED fabricated on pristine graphene anode and comparable to those of an ITO anode. A flexible polymer light-emitting diode (PLED) is demonstrated by using a bis(trifluoromethanesulfonyl)amide (TFSA, ([CF₃SO₂] ₂NH)) doped graphene anode. Due to a reduced hole-injection barrier from the graphene anode to the hole-transport layer, the maximum current efficiency and power efficiency of the PLED are markedly higher than those of PLEDs fabricated on pristine graphene anode and comparable to those of an ITO anode.