Improved Performance of Polymer: Polymer Solar Cells by Doping Electron-Accepting
Polymers with an Organosulfonic Acid
Sungho Nam1, Minjung Shin1,4, Hwajeong Kim1,*, Chang-Sik Ha2, Moonhor Ree3,
*,Youngkyoo Kim1
Article first published online: 22 SEP 2011
Abstract
The performance of polymer:polymer solar cells that are made using blend films of poly(3hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co- benzothiadiazole (F8BT) is
improved by doping the F8BT polymer with an organosulfonic acid [4-ethylbezenesulfonic
acid (EBSA)]. The EBSA doping of F8BT, to form F8BT-EBSA, is performed by means of a twostage reaction at room temperature and 60°C with various EBSA weight ratios. The X-ray
photoelectron spectroscopy measurement reveals that both sulfur and nitrogen atoms in
the F8BT polymer are affected by the EBSA doping. The F8BT-EBSA films exhibit huge
photoluminescence quenching, ionization potential shift toward lower energy, and greatly
enhanced electron mobility. The short-circuit current density of solar cells is improved by ca.
twofold (10 wt.% EBSA doping), while the open-circuit voltage increases by ca. 0.4 V.
Consequently, the power conversion efficiency was improved by ca. threefold, even though
the optical density of the P3HT:F8BT-EBSA blend film is reduced by 10 wt.% EBSA doping due
.to the nanostructure and surface morphology change