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Magnetic and optical studies of poly(3-hexylthienylene) (P3HT), doped in solution with NO+PF6ĩ n both chloroform and in the more polar solvent methylene chloride (CH2C12), indicate a relatively small difference in the energy of polarons versus that of bipolarons and imply that the weak effective electron-electron Coulomb repulsion can be controlled by varying the solvent and/or the polymer concentration. As a result, we have observed unambiguous magnetic and optical signatures characteristic of polarons in P3HT in CH2C12 at the lowest doping levels. The relative fraction of polarons and bipolarons has been analyzed in the context of various proposed statistical models. A theoretical model is developed to include the effect (in such solutions) of ionic screening on the effective Coulomb interaction. This model is tested by adding salt to a dilute solution of doped polymer.