The belief that Mary never committed sin has been around a long time, much longer than the final formulation of the doctrine of her immaculate conception (which happened around the 13th century). Augustine (d. 430), despite his doctrine of original sin, apparently carved out an exception for her, as summarized in the Encyclopedia of Ancient Christianity's entry on Mary:
Augustine, drawn into the problem of Mary’s holiness by Pelagius, affirms against the opinion of his adversary that Mary, propter honorem Domini, is the only woman without sin (De nat. et gratia 36,42).
On the other hand, Augustine's contemporary John Chrysostom (d. 407) apparently didn't go quite so far:
Even John Chrysostom (d. 407), although attributing some imperfection to Mary, nonetheless holds her up as the example of the woman who overcomes human weaknesses (Co. Io. 20-21).
I'd like to know if any after Chrysostom believed that Mary committed sin. I'd guess that the influence of Augustine would reduce the likelihood of finding this view in the West, but perhaps one or more fathers in the East continued to hold that she was less than morally perfect.
This question follows typical definitions of what a "church father" is, but to spell it out, they are "ancient and generally influential Christian theologians" (as Wikipedia says), not those closely associated with heretical movements (such as the Pelagian Julian of Eclanum), and not the anonymous authors of popular apocryphal stories. And we'll say that the last of the church fathers is John of Damascus (d. 749).