The importance of P3HT crystallite orientation for charge transport in solar cells

COLL 91

Michael D. McGehee, mmcgehee@stanford.edu1, Alex C. Mayer, acmayer@stanford.edu1, Brian E. Hardin, bhardin@stanford.edu1, and Michael F. Toney, mftoney@slac.stanford.edu2. (1) Department of Materials Science and Engineering, Stanford University, 476 Lomita Mall, Stanford, CA 94305, (2) Stanford Synchrotron Radiation Lab, Menlo Park, CA 94025
Bulk heterojunction solar cells based on poly(3-hexylthiophene) (P3HT) and phenyl-c61-butyric acid methyl ester (PCBM) have demonstrated a drastic increase in their power conversion efficiency as researchers gain control of the nanostructured morphology. Recently, it has been shown that decreasing the evaporation rate of the solvent in P3HT:PCBM leads to an increase in the hole mobility accompanied by an increase in solar cell efficiency. The mechanisms behind this mobility increase remain a puzzle. We have employed x-ray scattering and temperature-dependent diode mobility measurements of pure P3HT and P3HT:PCBM films spun from slow and fast drying solvents. We show that the orientation of the P3HT domains, in both the pure films and the blends, is highly dependent on the evaporation rate of the solvent, and that the orientation of the crystallites is the dominant effect controlling charge transport perpendicular to the substrate.
 

Interfacial Electron Transfer and Solar Energy Conversion: From Molecules to Nanomaterials
8:20 AM-12:00 PM, Monday, April 7, 2008 Morial Convention Center -- Rm. 226, Oral

Division of Colloid & Surface Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008