This article reports the main origin of the low luminescent efficiency in hole-dominant polymer light-emitting diodes by controlling the hole injection and by chemically modifying the cathode by molecular monolayers. Since molecular modification of the top electrode is impossible when one deposits the electrode using a vacuum deposition method, this study was performed using a soft contact lamination technique to form electrical contacts on top of the emissive layer. The top electrode was chemically modified with an alkane thiol self-assembled monolayer (SAM) to act as an interfacial spacer layer between the emitting layer and the cathode. Herein, it is reported that, contrary to common belief, a high device quantum efficiency can be achieved from the dominantly hole-transporting device with a high work-function cathode (like An) by facilitating more hole injection from the anode in the device with low population of exciton quenching channels near the cathode.