Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/MoO₃ composite layer for efficient and stable hole injection in organic semiconductors

We report a composite hole injection layer (HIL) composed of an ultrathin film of MoO₃on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) for efficient and stable hole injection in organic semiconductors. The optimized thickness of MoO₃ layer was determined to be about 0.5 nm, which was enough to increase the work function of the underlying films substantially. The composite HIL can inject holes efficiently into a variety of hole transport layers (HTLs), even that with very deep highest occupied molecular orbital (HOMO) levels. Moreover, the utilization of PEDOT:PSS/MoO₃ composite HIL greatly improved the stability of hole injection in organic devices, as compared to those based on pure PEDOT:PSS or MoO₃ HILs, beneficial to practical applications.