PEDOT layers with electronic functions

Poly(3,4-ethylenedioxythiophene) as a hole injection layer in OLEDs 

Since the pioneering work of Tang and VanSlyke [128], LEDs made with organic materials (OLEDs) have rapidly attracted interest in the scientific literature, industry and the media. The potential use of OLEDs in flat panel displays has encouraged numerous scientific and industrial efforts to realize this new technology. The introduction of conjugated polymers as emitting materials by Friend and co-workers [129], which led to polymeric OLEDs or PLEDs, was one of the milestones in the development of OLEDs. 

In 1992, Heeger and co-workers reported that an inherently conductive polymer such as polyaniline (PAni) could be used as a transparent anode material instead of ITO to make all-polymer, flexible OLEDs on plastic substrates [130, 131]. Later work suggested that PAni could also serve as an interlayer between the ITO anode and the emissive polymer to improve hole injection in OLEDs, leading to devices with higher brightness and better efficiency [132-136]. PEDOT was then introduced as a PAni alternative 

The advantage of incorporating PEDOT PSS buffer layers in OSCs is based on several properties closely related to its beneficial use in OLEDs [113, 150, 151], 

PEDOTiPSS planarizes the ITO surface by smoothing surface imperfections and reducing the root-mean-square roughness, e.g. from 10 nm for bare ITO to 3 nm for a 50 nm layer of PEDOT PSS on ITO [152]. Therefore, a PEDOT PSS buffer layer will typically increase the yield of functional devices as the probability of electrical shortages within the active layer is reduced [139, 153], 

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