Effect of crystallinity on UV degradability of poly[methyl(phenyl)silane] by energy-resolved electrochemical impedance spectroscopy

Low stability and degradability of polymers by ambient air, UV irradiation or charge transport are major problems of molecular electronics devices. Recent research tentatively suggests that the presence of a crystalline phase may increase polymer stability due to an intensive energy trapping in the ordered phase. Using the UV degradability, we demonstrate this effect on an archetypal model σ bonded polymer - poly[methyl(phenyl)silane] (PMPSi) - with partially crystalline and amorphous-like layers. UV degradation with 345 nm, derived from the branching state generation rate, was inversely proportional to the crystalline phase content, changing from 4.8x1011 s-1 (partially crystalline phase) to 1.8x1013 s-1 (amorphous-like phase). A model is proposed where crystallites formed by molecular packing act as effective excitation energy traps with a suppressed nonradiative recombination improving thus PMPSi film stability. The molecular packing and higher crystalline phase proportion may be a general approach for stability and degradability improvement of polymers in molecular electronics.