Hole injection improvement in organic light emitting diodes: PEDOT:PSS VS CuPc

In present paper, we investigate the effect hole injection layer in the improvement of the performance of organic light-emitting diodes (OLEDs). In particular, the capability of a spin-coated polymer containing polythiophene is compared with the functionality of the Copper(II) phthalocyanine small molecule which is deposited by thermal evaporation. In first step, a reduction from 11.4v to 8.5v is obtained in turn-on voltage of the device by incorporation of calcium as cathode electrode. Next, The effect of adding different hole injection layer diode structure to improve the performance of the device was examined. The functionality of the injection layers are examined by measuring different characteristics, namely current density-voltage, electroluminescence spectra, emission intensity, device lifetime, and current efficiency. Device with Copper(II) phthalocyanine presents superior characteristic comparing to the device which employs polythiophene based conducting polymer; i.e. reduction in turn-on voltage from 8.5v to 6.5v, increase in emission intensity from 1160 cd/m2 to 1600 cd/m2, increase in device lifetime from 72 to 94 hours, and finally enhancement in current efficiency from 0.2 cd/A to 0.6 cd/A.