The possibility of low-cost roll to roll fabrication procedures of organic solar cells using poly-3-hexyl-thiophene (P3OT) solutions has attracted intensive research in order to understand the process of self-organization of the polymers because the final morphology of the films at the nanoscale affects strongly the final macroscopic performance of the devices. With this SANS experiments we propose to characterize the process of aggregation of P3HT in different solvents at several temperatures. Initial measurements have demonstrated the onset of a coil-globular transition. A detailed study of P3HT and P3HS (the same polymer with Se instead of S) will shed light on this structural changes and contribute to the improvement of the fabrication of better organic solar cells.