Influence of Co-Solvents on the Performance of Polymer/Polymer Solar Cells

We report the influence of co-solvent compositions on the performance of polymer/polymer solar cells. Regioregular poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) were employed as an electron-donor and an electron-acceptor, respectively, for the fabrication of polymer/polymer solar cells. As a co-solvent system, we introduced p-xylene (XL) and tetrahydrofuran (THF) because the boiling point difference of these two solvents is approximately 40 °C. To understand the device performance change according to the co-solvent compositions, the P3HT:F8BT blend films were examined by optical absorption spectra, photoelectron yield spectra, and surface morphology measurements. The results showed that the co-solvent with 30 vol.% THF exhibited the highest power conversion efficiency due to the improved light-harvesting and charge transport.