A method of producing a structure comprising a substrate (11) having at least one integral first face at a first angle relative to a normal from the substrate, at least one second integral second face at a second angle relative to a normal from the substrate; with a cavity in the structure between the first and second faces; the method comprising the steps of: coating a portion (15) of the first face with a first conducting layer; coating a portion (18) of the second face with a second conducting layer; and depositing in the cavity an active material (31) to provide ohmic and rectifying contacts for insertion or extraction of charge from the active material by way of the first and second conducting layers. The active material may be photovoltaic, light emitting or ion conducting.