Influence of UV radiation and ozone exposure on the electro-optical properties and nanoscale structure of P3OT films

The modification of the nanoscale morphology and electronic behavior as well as the mesoscopic optical properties of thin films of poly-3-octyl-thiophene (P3OT) has been studied as these films are irradiated by ultraviolet light (UV). Films of about 100 nm thickness were prepared by spin-casting a P3OT solution in toluene on glass substrates. The samples were characterized by non-contact scanning force microscopy (NC-SFM), and by optical transmission measurements for every cycle of UV irradiation. Our experimental technique allows us to perform a nanoscale study of precisely the same area of the sample in order to correlate the effect of UV irradiation to specific morphological variations rather than to variations of the statistical properties of the sample. In addition, the decrease of film thickness is measured and correlated to the observed variation of optical absorption.

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► The UV/O3 modification of the nanoscale morphology, electronic and optical properties of P3OT thin films has been studied.
► Our setup allows us to correlate UV/O3 effect to true sample changes rather than to variations of the statistical properties of the sample.
► We conclude that nanoscale degradation of P3OT thin films when irradiated by UV light occurs in two steps.
► In a first initial process a chemical reaction with O3 generated by the UV irradiation varies the optical absorption and the contact potential.
► In a second step, the films are etched away by further chemical reaction with O3.