Spatial Fourier‐Transform Analysis of the Morphology of Bulk Heterojunction Materials Used in “Plastic” Solar Cells

Spatial Fourier transforms and power spectral density were used to analyze digital TEM images of bulk heterojunction material based on poly(3-hexylthiophene) as donor and a soluble fullerene (PCBM) as acceptor. Optimized high-temperature annealing leads to well-defined nanoscale (< 20 nm) interpenetrating networks (see figure). The power spectral density provides a detailed and quantitative description of the bulk heterojunction material and the kinetics of the phase separation.