NOVELTY - Electronic and opto-electronic circuits are printed by forming uniform and continuous film of film-forming precursor species onto a surface of a substrate; and altering portions of the film with conductivity-altering specie(s) to form regions having a second electrical conductivity that is different than first electrical conductivity of the film.    USE - The method is for printing electronic and opto-electronic circuits for printed circuit applications (claimed), e.g. polymer light emitting diodes for large displays or continuous-roll process for solar cells; electronic memories (write once or rewriteable; electronically addressable displays; or any circuit for which organic electronics or opto-electronics are acceptable.    ADVANTAGE - The method employs very simple and continuous processes, which make the time to produce a batch of circuits very short and leads to very inexpensive products. It avoids those traditional lithography-deposition-etching methods; minimizes environmental toxic chemicals usage; simplifies the manufacturing processes; and allows organic materials with appropriate electronic or opto-electronic properties to be printed to the flexible substrate to produce complex two- and three-dimensional structures that will enable circuits of essentially arbitrary complexity to be built.    DETAILED DESCRIPTION - Printing of electronic and opto-electronic circuits involves:    (1) providing a substrate onto which a circuit will be formed; providing a film-forming precursor species;    (2) forming uniform and continuous film (10) of the film-forming precursor species onto a surface of the substrate, the film having a first electrical conductivity; and    (3) altering portions of the film with conductivity-altering specie(s) (22) to form regions having a second electrical conductivity that is different than the first electrical conductivity, thus providing circuit elements for the electronic and opto-electronic circuits.    DESCRIPTION OF DRAWING(S) - The figure is a side elevational view showing the formation of dopants on the surface of a molecular layer.    Uniform and continuous film (10)    conductivity altering species (22)    De-dopant (24)