NOVELTY - In a sheet structure comprising a supporting element (SE) for a viscous coating material (VCM), the SE is formed from a grating material (GM) having a lattice spacing and interfacial tension relative to the VCM adapted so that after coating the lattice openings of the GM are covered by a skin of VCM, which dries to give a crack-free covering film of VCM.    USE - The sheet structure is specifically a component of a photovoltaic element (claimed), such as a solar cell, photocell or light-emitting diode, especially a dye sensitized solar cell (DSSC).    ADVANTAGE - Polymer-based sheet structures (especially flexible photovoltaic elements) are obtainable by a simple procedure. In particular highly mobile viscous media (such as semiconducting mixtures of fullerene and poly-(3-hexyl-thiophene)) as VCM can be applied and printed onto self-supporting gratings with high accuracy and in an efficient and inexpensive manner.    DESCRIPTION OF DRAWING(S) - The figures show a schematic plan view (not to scale) of a polymer-based photovoltaic element incorporating a sheet structure; and a greatly enlarged section (not to scale) through the same photovoltaic element.    Photovoltaic element (10)    First and second electrodes (12, 14)    Photovoltaically active laminate, of viscous material (16)    Self-supporting grating electrode (18)    Lattice openings (20)    Skin of viscous coating material (22)    Hole blocking surface coating, e.g. of titanium oxide (24)    Uncoated section of grating electrode (26)    First and second contacting elements (28, 42)    Non-coated contact regions of grating electrode (30)    Layer of semiconductor, e.g. mixture of fullerene (PCBM) and poly-(3-hexyl-thiophene) (P3HT) (32)    Layer of electron blocking material, e.g. poly-(3,4-ethylenedioxy-thiophene)-poly-(styrenesulfonate) (PEDOT-PSS) (34)    Uncovered region of semiconductor layer (36)    Uncovered regions of electron blocking layer (38, 40)    Lattice spacing of grid electrode (A)    Applied potential (U)