Comprehensive study of the influence of different environments on degradation processes in F8BT: Correlating optoelectronic properties with Raman measurements

Abstract

There is a growing interest in conjugated polymers from both industrial and academic points of views. The reasons are their tunable optoelectronic properties, ease of production, and excellent mechanical properties. However, the ease with which their optoelectronic properties are tunable make devices based on them prone to fast degradation and therefore, short life time. The issue of degradation of organic based optoelectronic devices is the topic of many ongoing researches. However, much less attention is given to degradation processes of the individual components of the devices and their dependence on the environmental conditions. In this work, we report on the degradation of a film of a polyfluorene block copolymer F8BT that is used in a variety of optoelectronic devices under different environments: Sun exposure, heating, and UV exposure in inert and ambient conditions. Degradation was observed in most of the optoelectronic properties of the film. Topographic measurements did not show observable changes of the film morphology following degradation. However, Raman spectroscopy measurements show changes that indicate degradation in one of the building blocks of the copolymer that is associated with electron's conduction. The absolute value of the correlation coefficient between the decrease in the Raman signal and the decrease in the optoelectronic properties is larger than 0.95 under sun exposure it is larger than 0.8 under all other ambient exposures and smaller than 0.65 under inert conditions. These results support the assumption that Oxygen, not necessarily through photo-oxidation, and also water play an important role in the degradation process and indicate the part of the polymer that is most susceptible to degradation.

Complex Photobleaching Behavior of Semiconducting Polymer Dots

“…Poly(fluorene) polymers degrade in the presence of oxygen to form keto (9-fluorenone) defect sites, with a possible carboxyl defect as an intermediate. 66,67 Photodegradation of CPs is also known to occur in the absence of oxygen, including for F8BT, 68,69 other poly-(fluorenes), 70 PH3T, 71 other thiophenes, 72 and PPV-type polymers. 73 In general, the degradation has been attributed to cross-linking and other reactions involving radicals (e.g., chain scissions, Norrish, photo-Fries).…”

“…Indeed, other studies have suggested that poly(fluorenes), and particularly F8BT, have better resistance to photooxidation than many other types of CPs. 68,84,85 In practice, the PB of Pdots will need to be addressed by multiple strategies. When compatible with optical requirements, judicious selection of the CP will be important.…”

Microscopic Investigation of Degradation Processes in a Polyfluorene Blend by Near-Field Scanning Optical Microscopy

“…This rapid degradation is mostly due to the lower resistance of these organic polymers to environmental conditions such as air and moisture . Much work has been done in order to optimize optoelectronic devices by understanding degradation mechanisms and their role determining device stability and lifetime. − Two main mechanisms of degradation in polyfluorenes are reported in the literature. The first is the formation of fluorenone defect sites (known as keto defects) that act as low-energy (green-band) trapping sites for singlet excitons, which quench the fluorescence.…”

Electrically Injected Hybrid Organic/Inorganic III-Nitride White Light-Emitting Diodes with Nonradiative Förster Resonance Energy Transfer

“…The top-down fabrication process is thus completed with the deposition of F8BT to fill into the arrayed microholes. Organic materials are highly susceptible to degradation in the presence of atmospheric moisture and oxygen, resulting in permanent emission quenching . To mitigate this organic material processing is completed within an anaerobic (O 2 < 0.5 ppm) glovebox environment with hydrogen gas (H 2 ) < 5% in nitrogen (N 2 ).…”