NOVELTY - Fabricating an organic semiconductor device, comprises processing a single component conjugated polymer, in a presence of a processing additive and onto a substrate. The single component conjugated polymer: processed onto the substrate is fabricated into an active region of an organic device on the substrate; and comprises a donor and an acceptor, or donor and acceptor repeating units.    USE - The method is useful for fabricating an organic semiconductor device that is a solution processed field effect transistor (FET) (all claimed), organic photovoltaic device, organic LED, transistor and organic solar cell.    ADVANTAGE - The method increases a carrier mobility in the active region of the organic semiconductor device compared to a control device where: the conjugated polymer is processed without the additive; the hole mobility in a saturation regime (saturation hole mobility) is increased by a factor of least 6, as compared to the control FET's saturation hole mobility of no less than 1.3x 10-4 cm2/Vs, or by a factor of at least 1.7, as compared to the control FET's hole mobility of no less than 2.3x 10-1 cm2/Vs; an output current in a saturation regime of the FET is increased by a factor of at least 1 .6, compared to a control FET having an output current in a saturation regime of no less than 22 mu A; an on/off (Ion/Ioff) ratio of the FET is increased by a factor of at least 10, compared to a control FET's on/off ratio of no less than 104; and a threshold voltage magnitude of the FET is reduced, compared to a control FET's threshold voltage magnitude of no more than 30 Volts. The lifetime of the device is increased compared to a control device.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a composition comprising the processing additive and the single component conjugated polymer; and    (2) an organic semiconductor device comprising an active region including the single component conjugated polymer processed using the processing additive.    DESCRIPTION OF DRAWING(S) - The figure shows a flowchart illustrating a method of fabricating an organic device.    Adding additive to polymer (100)    Obtaining composition (102)    Obtaining substrate (104)    Depositing composition on substrate (106)    Annealing (108)