title: Influence of the ionic functionalities of polyfluorene derivatives as a cathode interfacial layer on inverted polymer solar cells.
abstract: In this work, we synthesized water-soluble polyfluorene derivatives (WPFs) with anionic and/or cationic side chains, which were used as an indium tin oxide (ITO) cathode interfacial layer in inverted polymer solar cells. Three WPFs (WPFN+, WPFZW, and WPFS-) were obtained via Suzuki coupling reactions. Their solubility in polar solvents allowed the WPFs to be used as interfacial layers in inverted polymer solar cells (I-PSCs). Among the WPF-modified ITO electrodes, WPFN+ (with ammonium side chains)-modified ITO can be used as a cathode for electron extraction, while WPFS- (with sulfonate side chains)-modified ITO cannot extract electrons in I-PSCs based on poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM). The electron extraction of WPF-modified ITO can mainly be attributed to the different dipole formations at the WPF/ITO interfaces, based on the types of ionic groups on the side chains of the polyfluorene. In addition, we observed that the extent of ITO work-function modification was not always exactly correlated with the device performance based on the results obtained using a WPFZW (with ammonium and sulfonate side chains)-modified ITO electrode.
authors.affiliation: Heeger Center for Advanced Materials (HCAM), School of Materials Science and Engineering and ‡Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology , 1 Oryong-Dong, Buk-Gu, Gwangju 500-712, Republic of Korea.
authors.forename: Rira
authors.initials: R
authors.lastname: Kang
authors.forename: Seung-Hwan
authors.initials: SH
authors.lastname: Oh
authors.forename: Dong-Yu
authors.initials: DY
authors.lastname: Kim