Highly　efficient　flexible　organic　light-emitting　diodes　(OLEDs)　fabricated　by　utilizing　inkjet　printing　technique　are　demonstrated　in　this　work.　A　strategy　of　hybrid　hole　injection　layer　is　employed　to　improve　the　device　efficiency,　where　the　polyethylene　glycol　(PEG)　is　used　to　modify　the　energy　level　and　conductivity　of　the　conventional　hole　injection　layer　poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)　(PEDOT:PSS),　which　regulates　the　amount　of　holes　entering　the　organic　light-emitting　layer,　realizes　the　injection　balance　of　carriers,　and　nearly　doubles　the　green　device　efficiency　with　the　record　high　maximum　external　quantum　efficiency　(EQE)　of　9.45%　and　the　current　efficiency　of　28　cd/A.　Moreover,　the　introduction　of　PEG　improves　the　mechanical　properties　of　PEDOT:　PSS　and　improves　the　bending　resistance　of　the　device.　A　highly　efficient　flexible　white　OLED　device　is　realized　by　using　inkjet　printing　based　on　the　PEG-modified　PEDOT:PSS　hole　injection　layer,　achieving　the　maximum　EQE　of　4.8%.　In　addition,　a　1-inch　white　OLED　array　device　is　realized　on　the　flexible　substrate,　which　further　confirm　the　feasibility　of　large-scale　production　for　inkjet　printed　flexible　devices.　©　2020　Elsevier　B.V.