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Reported herein are solution-processed polymer anode electrodes for blue phosphorescent organic light-emitting diodes (PhOLEDs). The highly conductive anodes were made from 10-wt%-methylred-(MR)-doped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (PH1000) films. The red-colored and uniform polymer films demonstrated electrical conductivity values that significantly increased from 0.25 to 50 S•cm −1 after doping. The more than 200-fold enhancement in conductivity indicates that the doped films have a lower sheet resistance and better hole injection and transport properties than the pristine films. The resultant PhOLEDs based on the doped polymer anodes exhibited stable, broad, and intense blue emission at 468 nm with a 2616 cd•m −2 maximum luminance and a 4 V turn-on voltage. The obtained study results confirmed the effectiveness of the MR dye as a dopant for the significant enhancement of the conductivity and effective hole injection of PEDOT:PSS. Efficient future flexible optoelectronic applications can be built using this highly conductive polymer electrode obtained via a simple, solution-processed, and cost-effective doping approach.

The stability of doped organic semiconductors is one of the essential features to achieve stable and high-performance organic optoelectronic devices with low power consumption. In this study, the thermal degradation of an organic homojunction, consisting of an intrinsic organic layer and a molybdenum oxide (MoO3)-doped organic layer, is investigated by impedance spectroscopy (IS) under thermal heating. The IS analysis indicates that the thermal deformation of the intrinsic organic layer is more significant than that of the underlying doped organic layer. A charge-transfer complex absorption peak analysis by ultraviolet-visible spectroscopy confirms that the thermal degradation is related to the deformation of organic host molecules rather than to diffusion of dopants. These results show that the organic homojunction is degraded owing to the crystallization of intrinsic organic molecules at high temperatures, above the glass transition temperature (Tg), rather than because of disruption of the interface at the homojunction by dopant diffusion. This study shows that hole-transport molecules having high Tg should be selected to provide stable electronic devices with organic homojunctions, thus paving the way for the development of novel devices with higher performance.