Self-Assembled Hybrid Polymer−TiO2 Nanotube Array Heterojunction Solar Cells

• Published in: Langmuir 2007-11, Vol.23 (24), p.12445-12449
• Main Authors: Shankar, Karthik, Mor, Gopal K, Prakasam, Haripriya E, Varghese, Oomman K, Grimes, Craig A
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Cross-disciplinary physics: materials science; rheology; Electrochemistry; Electrolytes - chemistry; Ethylene Glycol - chemistry; Exact sciences and technology; Fullerenes - chemistry; Fullerenes and related materials; diamonds, graphite; General and physical chemistry; Materials science; Microscopy, Atomic Force; Nanotechnology - methods; Nanotubes - chemistry; Nanotubes - radiation effects; Photochemistry; Physics; Solar Energy; Solutions - chemistry; Specific materials; Spectrum Analysis; Surface physical chemistry; Surface Properties; Thiophenes - chemistry; Time Factors; Titanium - chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la7020403

Films comprised of 4 μm long titanium dioxide nanotube arrays were fabricated by anodizing Ti foils in an ethylene glycol based electrolyte. A carboxylated polythiophene derivative was self-assembled onto the TiO2 nanotube arrays by immersing them in a solution of the polymer. The binding sites of the carboxylate moiety along the polymer chain provide multiple anchoring sites to the substrate, making for a stable rugged film. Backside illuminated liquid junction solar cells based on TiO2 nanotube films sensitized by the self-assembled polymeric layer showed a short-circuit current density of 5.5 mA cm-2, a 0.7 V open circuit potential, and a 0.55 fill factor yielding power conversion efficiencies of 2.1% under AM 1.5 sun. A backside illuminated single heterojunction solid state solar cell using the same self-assembled polymer was demonstrated and yielded a photocurrent density as high as 2.0 mA cm-2. When a double heterojunction was formed by infiltrating a blend of poly(3-hexylthiophene) (P3HT) and C60-methanofullerene into the self-assembled polymer coated nanotube arrays, a photocurrent as high as 6.5 mA cm-2 was obtained under AM 1.5 sun with a corresponding efficiency of 1%. The photocurrent action spectra showed a maximum incident photon-to-electron conversion efficiency (IPCE) of 53% for the liquid junction cells and 25% for the single heterojunction solid state solar cells.