High-Efficiency Polymer Solar Cells with Water-Soluble and Self-Doped Conducting Polyaniline Graft Copolymer as Hole Transport Layer

A graft copolymer, poly(styrene sulfonic acid) grafted with polyaniline (PSSA-g-PANI), is synthesized and used as the hole transport layer in polymer solar cells based on poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester. Electrochemical stability of PSSA-g-PANI is superior to poly(3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS), which has widely been used as the hole transport material in polymer solar cells. The unique high transparency in 450-650 nm wavelength and high electrical conductivity of PSSA-g-PANI result in higher short circuit current and higher open circuit voltage of polymer solar cells than those of the device made of PEDOT:PSS. A series of PSSA-g-PANI with different electrical conductivities are synthesized to investigate the effect of conductivity on the performance of polymer solar cells. The device with the most conductive PSSA-g-PANI exhibits the highest power conversion efficiency (similar to 4%), which is 20% higher than that of the device with PEDOT:PSS.