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.