To evaluate the impact of film modification on the electronic performance, bottom-gate bottom-contact (BGBC) organic field effect (OFET) devices were fabricated. Using field-effect measurements, the saturated hole mobilities were extracted from transfer curves using the gradient of Ids 1/2 against Vg (Supplementary Figure ). The pristine pDPP3T film exhibited an average hole mobility (μh) of 10.4 × 10 - 2 cm 2 V -1 s -1 ; shown as the upper limit when comparing the effect of UVO treatment on OFET mobility in Figure . Upon short exposure of the films to ozone treatment (5 s and 30 s), the hole mobility is remarkably well maintained compared with the pristine film. However, with prolonged exposure times of 60 and 180 s, the mobility deteriorates by multiple orders of magnitude (1.67 × 10 -4 and 4.92 × 10 -5 cm 2 V -1 s -1 ). Additionally, devices exposed to UVO for t > 30 s did not exhibit transistor-like characteristics (inset, Figure ), as seen by the inability to charge devices upon application of Vg. In agreement with the observed changes in chemical composition via XPS and reduction in the relative absorption of the ICT band in the UV-vis, this provides further evidence for a significant decrease in the effective conjugation of the pDPP3T due to oxidation of the polymer backbone. Yet, these results highlight the ability to retain desirable charge transport properties whilst simultaneously optimizing the surface properties through UVO treatment.