It has been shown that poly(3-hexylthiophene) ($\mathrm{P}3\mathrm{HT}$) dissolved in chloroform ($\mathrm{CHC}{\mathrm{l}}_3$) undergoes efficient aggregation with permanent polaron formation when submitted to phototreatment mediated by visible pulsed radiation. Although the need for pulsed radiation has been addressed, the role of $\mathrm{CHC}{\mathrm{l}}_3$ in the aggregation process and permanent polaron formation has been elusive. Here we show that $\mathrm{CHC}{\mathrm{l}}_3$ is a major player in photoaggregated products because it undergoes dissociation into hydrogen chloride ($\mathrm{HCl}$) when submitted to high-energy radiation. $\mathrm{HCl}$ is a strong acid and binds to the $\mathrm{P}3\mathrm{HT}$ thiophene ring, establishing a required $p$-doped structure rich in counter ions that stabilize the polarons. UV-Vis absorption, photoluminescence, and Raman modes provide spectroscopic fingerprints, indicating that the planarization of polymeric chains occurs and that such planarization is maintained by the permanent polarons formed throughout the structure when they are present. We also show that methanol $\left(\mathrm{MeOH}\right)$ in an acidic environment works as a facilitator that enhances the efficiency of the polymeric doping process, polaron formation, and controllability of the aggregates' character.

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• Aggregation
• Doping effects
• Optoelectronics
• Polarons
• Polymer behavior
• Self-assembly
• Structural order parameter