An apparatus is provided for vapor deposition of a sublimated source material as a thin film on discrete photovoltaic (PV) module substrates conveyed in a continuous non-stop manner through said apparatus. The apparatus includes a vapor deposition head configured for receipt and sublimation of a source material, and for distributing the sublimated source material onto an upper surface of substrates conveyed through a deposition area. A roll seal configuration is provided at each of an entry slot and an exit slot for the substrates conveyed through the apparatus. The roll seal configuration further includes a cylinder rotatably supported at a defined gap height above a conveyance plane of the substrates such that the cylinder is not in continuous rolling contact with the substrates within the window of finished active semiconductor material. The cylinder is floatable in a vertical direction relative to the conveyance plane of the substrates such that the cylinder rolls up and over surface variations in the substrates that exceed the gap height as the substrates are conveyed under the cylinder.