We report the thermo-assisted dissolution of aggregated regioregular poly(3-hexylthiophene) (P3HT) in ortho-dichlorobenzene (o-DCB) at a concentration level that is typical for photovoltaic applications (20 mg/mL). Detailed investigation on electronic absorption and fluorescence spectroscopy revealed, for the dissolution of P3HT aggregates, a critical temperature regime (27-33 degrees C) with a middle-point temperature (T-m similar to 29 degrees C) and an aggregation-degree dependent endothermic dissolution enthalpy. In this temperature regime, pre-resonant Raman spectroscopy results showed a drastic variation of solvent-solute interaction in the solvation sphere of P3HT. In addition, an annealing treatment to the concentrated solution is proven to be rather effective in minimizing P3HT agglomeration. (C) 2015 Elsevier B.V. All rights reserved.