An Evaluation of Optical Absorbance Kinetics for the Detection of Micro-Porosity in Molecularly Doped Polymer Thin-Films

David Mitchell Goldie,Orlaith Skelton,Thomas James Bailey

doi:10.3390/solids2020010

Abstract

The use of optical absorbance kinetics to identify micro-porous regions in doped polymer films is evaluated. Data are presented for a series of hydrazone doped polymer films which are found to optically bleach upon exposure to an ultra violet (UV) radiation source. The UV absorbance kinetics are found to exhibit distinctive characteristics for the various polymers studied, with changes in film absorbance occurring either in a fast (<103 s) or slow (>104 s) timescale. An interpretation of these distinctive timescales based upon a cellular-automata model of the absorbance kinetics suggests that the underlying photo-oxidation of the hydrazone is highly sensitive to underlying micro-porosity in the films which controls the necessary supply of absorbed oxygen for photo-cyclic reaction.

Highlights

Thin-film organic materials have become increasingly important as the active electronic medium in a wide range of large-area imaging and display devices
The column entries for φf, τ f and τ s in Table 1 represent parameters that have been determined from analysis of the absorbance kinetics for these films and are defined in the results section
Relative to the ultra violet (UV) reference the spectral responses recorded for the molecularly doped polymers (MDPs) was films detected in the to recorded spectra to forlonger unexposed

Summary

Introduction

Thin-film organic materials have become increasingly important as the active electronic medium in a wide range of large-area imaging and display devices. An important class of such organic materials are molecularly doped polymers (MDPs) which comprise an electronically inert polymer binder into which an electrically active dopant molecule is dispersed. Careful chemical selection of the polymer-dopant combination, and optimisation of the dopant concentration, permits the benchmark mobility-lifetime (μτ) product to be sensitively controlled for the majority electronic carrier according to the target application. The long-term stability of such μτ magnitudes in MDPs may be seriously compromised, via unwanted internal chemical reactions. Such reactions are generally induced by internal photo-excitation processes and are significantly more damaging for the dopant molecules which are subsequently rendered to become electronically inactive

Methods

Results

Conclusion