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, 248 nm) in a commercial, excimer-laser micromachining workstation. By limiting the fluence in the pulse to ∼50 mJ/cm2 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 π-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.