Polyfluorene devices, performance improvement

Fig. 3.5. (a) The general structure of polyfluorenes, and (b) the variant F8T2. Polyfluorenes and many of their derivatives are liquid crystals which can be crystallized after deposition to improve the pi-pi overlap and device performance. The alkyl chains tethered to the fluorene group solubilize the material. 

These compounds provided the source material for the first blue OLEDs.72 However, these devices were short-lived. Yet devices fabricated with improved blue-emitting amino oxadiazole fluorene did exhibit greater efficiency and stability,9 although their performance was still inferior to that of polyfluorene-based PLEDs (see below). 

Abstract Poly(dibenzosilole)s are an emerging class of polymers with similar optoelectronic properties to polyfluorenes. With increased stability towards oxidation, several poly(dibenzosilole)-based devices, such as light emitting diodes, have shown improved performance over their polyfluorene counterparts. As a consequence of reduced conjugation in the polymer chain, some poly(dibenzosilole)s have high triplet excited state energies, which make them suitable hosts for blue triplet emitters in electrophosphores-cent devices. 

Poly(dibenzosilole)s are a relatively new class of compounds for the area of organic electronic materials. Poly(dibenzosilole)s are not easily oxidised and have advantages of solubility and processibility over other polyfluorene analogues, such as carbazoles, dibenzophosphole oxides and dibenzothiophene dioxides. Several groups have already incorporated poly(dibenzosilole)s in the latest organic electronic devices such as OLEDs, OFETs and OSCs and have found improved performance over similar polyfluorene-based devices. With continual advancement in their synthesis, dibenzosilole-based polymers are set to match the popularity of polyfluorenes in organic electronic materials. 

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