Although useful advances are being made in energy saving devices such as, for example, organic-based organic light emitting diodes (OLEDs), polymer light emitting diodes (PLEDs), phosphorescent organic light emitting diodes (PHOLEDs), and organic photovoltaic devices (OPVs), further improvements are still needed in providing better materials processing and/or device performance for commercialization. For example, one promising type of material used in organic electronics is the conducting polymers including, for example, polythiophenes. However, problems can arise with polymers' purity, processability, and instability in their neutral and/or conductive states. Also, it is important to have very good control over the solubility of polymers utilized in alternating layers of various devices' architectures (e.g., orthogonal or alternating solubility properties among adjacent layers in particular device architecture). These layers, for example, also known as hole injection layers (HILs) and hole transport layers (HTLs), can present difficult problems in view of competing demands and the need for very thin, but high quality, films.
In a typical OLED device stack, the refractive index for most p-doped polymeric HILs is around 1.5, such as HILs comprising PEDOT:PSS, while the emissive materials generally have a refractive index that is substantially higher (1.7 or higher). As a result, additional total internal reflection occurs at EML/HIL (or HTL/HIL) and HIL/ITO interfaces, leading to reduced light extraction efficiency.
There is an ongoing unresolved need for a good platform system to control properties of hole injection and transport layers, such as solubility, thermal/chemical stability, and electronic energy levels, such as HOMO and LUMO, so that the compounds can be adapted for different applications and to function with different compounds, such as light emitting layers, photoactive layers, and electrodes. Good solubility, intractability, and thermal stability properties are important. Also of importance is the ability to tune HIL resistivity and HIL layer thickness while retaining high transparency, low operating voltage, and/or high refractive index. The ability to formulate the system for a particular application and provide the required balance of such properties is also important.