Electronic structure of UV degradation defects in polysilanes studied by Energy Resolved – Electrochemical Impedance Spectroscopy

Abstract

The white photo luminescence after UV degradation in long wavelength range 400–600 nm was examined on the prototypical polysilane, poly[methyl(phenyl)silane], using both photoluminescence spectroscopy and a new method of Energy Resolved - Electrochemical Impedance Spectroscopy (ER-EIS). Two groups of defect states, situated at approximately 440 nm (ΔE1 = 2.8 eV with respect to electron transport energy) and 520 nm (ΔE2 = 2.4 eV with respect to electron transport energy) were found by both spectroscopic methods. The white radiative recombination is ascribed to the recombination from trapping sites following the extreme energy migration. The forming of the crosslinking and bridging defects after photochemical scission of SiSi via the series of various kinds of intermediates is feasible (silyl R3Si −380 nm, silylene Si2H4 − 480 nm, silene and silylsilylene −550 nm emissions). On the grounds of the IR absorption spectroscopy results we suppose the presence of the bonding by methylene bridging and carbosilane unit SiCH2Si creation after SiSi Si σ sp3 bond scission. The ER-EIS method turned out to be extremely suitable for elucidation of the electronic structure and its changes in organic semiconductors due to its great resolving power and wide range both in the energy and the density of electronic states.