Thermal-induced changes on the properties of spin-coated P3HT:C60 thin films for solar cell applications

The thermal transition behaviour, optical and structural properties of spin-coated P3HT:C60 blended films with different C60 ratios were investigated using differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), ultraviolet–visible (UV–vis) spectroscopy, photoluminescence (PL), Fourier transform infrared absorption (FT-IR) spectroscopy and Raman spectroscopy. DSC analysis showed that the P3HT:C60 blends have quite different thermal characteristics. The absorption spectra of the annealed P3HT:C60 (1:1 wt%) films becomes enhanced and red shifted. This feature is evident in the photoluminescence measurements where the formation of polymer crystallites upon annealing is observed. Raman spectroscopy showed a substantial ordering in the polymer film during annealing. It was found that the performance of a P3HT:C60 (1:1 wt%) device was dramatically improved by annealing.