Thick superconducting films ofYBa2Cu3O7−&dgr;grown by photoassisted metalorganic chemical vapor deposition that have shown a decrease ofJcwith increasing thickness (>1 &mgr;m) have been exposed to ion irradiation in an attempt to enhanceJc.A 4.5 &mgr;m thick film irradiated with 1 MeV protons at a dose of3×1014/cm2has shown an increase ofJcby a factor of nearly20–1.7×106 A/cm2corroborating the proposal that a lack of pinning centers in the grown thick films, due to their high crystalline quality, contributed to the observed decrease ofJcwith increasing film thickness. ©1997 American Institute of Physics.