This invention generally relates to improved methods of fabricating molecular electronic devices, in particular organic electronic devices such as organic light emitting diodes (OLEDs) by droplet deposition techniques such as ink jet printing. The invention also relates to molecular device substrates fabricated by and/or use in such methods.We describe an optical or optoelectronic device comprising a substrate and a plurality of discrete bank structures disposed on the substrate, wherein: each bank structure defines the perimeter of at least one well; one or more of a charge transporting, charge injecting, light-filtering and light-emitting material is disposed in the well; and at least one bank structure defines the perimeter of at least one well and does not extend to the perimeter of any adjacent well. Thus in embodiments no part of said perimeter defines the bank of more than one well.