Excimer-laser micropatterned photobleaching as a means of isolating polymer electronic devices

Results are reported of an investigation into the effects of UV irradiation on the electrical conductivity of poly(3-hexylthiophene) films and on the field-effect mobility in transistors formed from this semiconducting polymer. The UV Source used was a pulsed excimer-laser (KrF, 248nm) in a commercial, excimer-laser micromachining workstation. By limiting the fluence in the pulse to similar to 50 mJ/cm(2) controlled reductions of up to 2 orders of magnitude in both the bulk conductivity and field-effect mobility were achieved before significant ablation took place. Changes in the UV-vis spectrum of the P3HT show that reduced electrical transport is accompanied by an increase in the optical bandgap which is attributed to a reduction in pi-conjugation either by chain scission or photo-oxidation of the polymer. It is argued that photobleaching of selected regions of the semiconducting polymer film is a viable technique for isolating individual transistors in a polymer electronic circuit. (c) 2005 Elsevier B.V. All rights reserved.