PNAS Plus Significance Statements Unraveling the chromophoric disorder of poly(3-hexylthiophene)

Ideal photovoltaic cells would be black, absorbing all of the Sun’s radiation, whereas Nature’s machinery for solar energy harvesting— photosynthesis—looks green. Organic semiconductor devices, based on molecular building blocks, lie conceptionally between the extremes of inorganic and photosynthetic light harvesting. How can organic solar cells appear almost black if they are based on molecular units? Using single-molecule spectroscopy, we identify (pp. E3550–E3556) the fundamental electronic building blocks of organic solar cells and reveal that discrete molecule-like transitions scatter over the entire visible spectrum. The fundamental molecular unit is narrowband, but disorder induces a continuum reminiscent of that characterizing highly ordered inorganic crystals.