We studied the improvement of a polymer light-emitting diode (PLED) by inserting an interlayer between a poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) and an emissive layer. An octadecyltrichlorosilane (OTS) was treated on the PEDOT:PSS as the interlayer. It improved the device efficiency of the PLED from 4.4 to 5.3 cd/A, and increased the maximum luminance from 10,000 to 17,000 cd/m(2). It increased the forward current by 20% and reduced the reverse current by 80%. Inserting the OTS layer between PEDOT:PSS and the emissive polymer reduced the injection barrier between the PEDOT:PSS and emissive layer. Therefore, the increases of the effective work function of the anode led to better hole injection and thus, higher current density.