Abstract:
Organic light emitting diodes (OLEDs) have been a great interest of research
recently. A number of modifications are carried out for the development of OLEDs.
Charge accumulation at organic heterointerfaces studies using displacement
current measurements (DCM) have been already demonstrated. Extending these
studies to evaluate the effect of the UV-Ozone treatment on a hole-injection layer
(HIL) of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is
demonstrated. A simple green emitting OLED structure was used with tris (8-
quinolinolato) aluminum (Alq3) as emitter. Two devices were fabricated to
differentiate the effect of the exposure on the PEDOT:PSS. DCM measurements were
followed by current-voltage-luminance measurements. PEDOT:PSS was spin casted
on to two slides of SiO2 and then controlled UV – O3 exposure to measure the
morphology changes. The study shows improved luminance levels up to ~25 cd/m2
from the treated device. Interface charge was calculated under the 100 V/s sweep
rate as -0.86 mA/m2, where ~ 1.1 mA/m2 of interface charge for the non-treated.
Above results corresponds to the quasi static state of the device. Transient state of
the device was analysed using sweep rate dependence in order to acquire data
about contact resistance, which was not visible. AFM results suggested a reduction
in the PEDOT:PSS layer, etched which must be resulted upon the exposure. The
exposure is reported for work function tuning of the PEDOT:PSS and here it is
revealed that exposure will reduce the interface charge at the interface, which leads
to the improvement of efficiency.
