Closely spaced, high aspect-ratio gridline structures are formed on the surface of a substrate using two or more co-extrusion heads that co-extrude gridline material and sacrificial material such that the deposited gridline material is compressed between opposing portions of the sacrificial material. The co-extrusion heads include three-channel cavity structures that converge to a relatively small outlet orifice that dispenses the gridline material with relatively fine features and a relatively high aspect ratio. The outlet orifices of the co-extrusion heads are disposed in a staggered arrangement such that gridlines extruded from the first co-extrusion head are disposed between two gridlines extruded from the second co-extrusion head. Photovoltaic cells are produced with metal gridlines formed in this manner.