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We report that adding a thin (∼10nm) semiconducting polymer interlayer between apoly(styrenesulphonate)-doped poly(3,4-ethylenedioxythiophene) (PEDT:PSS) hole transporter and an emissive semiconductor significantly improves the device efficiency of polymer light-emitting diodes (LEDs). With the interlayer, the external quantum efficiency (EQE) increases from 0.7%(0.4cd∕A at 3.7V) to 1.9% (1.0cd∕A at 3.3V) at 100cd∕m2 for red LEDs and from 1.9%(6.2cd∕A at 3.4V) to 3.0% (10.1cd∕A at 3.0V) at 1000cd∕m2 for green LEDs. An EQE of 4.0% is also observed in blue LEDs (35% increase). The interlayer is spin-coated directly on top of the PEDT:PSS layer from a poly(2,7-(9,9-di-n-octylfluorene)-alt-(1,4-phenylene-((4-sec-butylphenyl)imino)-1,4-phenylene)) (TFB) solution. This interlayer prevents significant quenching of radiative excitons at the PEDT:PSS interface by acting as an efficient exciton blocking layer.