title: Enhanced air stability of polymer solar cells with a nanofibril-based photoactive layer.
abstract: In spite of the rapid increase in the power conversion efficiency (PCE) of polymer solar cells (PSCs), the poor stability of the photoactive layer in air under sunlight is a critical problem blocking commercialization of PSCs. This study investigates the photo-oxidation behavior of a bulk-heterojunction (BHJ) photoactive film made of single-crystalline poly(3-hexlythiophene) (P3HT) nanofibrils and fullerene derivatives [phenyl-C61-butyric methyl ester (PCBM), indene-C 60 bisadduct (ICBA)]. Because the single-crystalline P3HT nanofibrils had tightly packed π-π stacking, the permeation of oxygen and water into the nanofibrils was significantly reduced. Chemical changes in P3HT were not apparent in the nanofibrils, and hence the air stability of the nanofibril-based BHJ film was considerably enhanced as compared with conventional BHJ films. The chemical changes were monitored by Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and UV-vis absorbance. Inverted PSCs made of the nanofibril-based BHJ layer also showed significantly enhanced air stability under sunlight. The nanofibril-based solar cell maintained more than 80% of its initial PCE after 30 days of continuous exposure to sunlight (AM 1.5G, 100 mW/cm(2)), whereas the PCE of the conventional BHJ solar cell decreased to 20% of its initial PCE under the same experimental conditions.
authors.affiliation: Department of Materials Science and Engineering, Yonsei University , 134 Shinchong-dong, Seoul 120-750, Republic of Korea.
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Oh
authors.forename: Minkwan
authors.initials: M
authors.lastname: Shin
authors.forename: Hyun Woo
authors.initials: HW
authors.lastname: Lee
authors.forename: Yu-Jeong
authors.initials: YJ
authors.lastname: Lee
authors.forename: Hong Koo
authors.initials: HK
authors.lastname: Baik
authors.forename: Unyong
authors.initials: U
authors.lastname: Jeong