Excitons in crystalline thin films of 3,4,9,10-perylenetetracarboxylic dianhydride studied by photocurrent response

We study excitons in crystalline thin films of the archetype molecular compound: 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) by measuring the photocurrent response under small electric fields (< 104 V/cm). A previously uncharacterized exciton at a wavelength of λ = 590 nm, or at 2.10 eV above the PTCDA highest occupied molecular orbital, is identified. Lower in energy than either of the previously observed charge transfer excitons at λ = 475 and 555 nm in PTCDA, the λ = 590 nm exciton is speculated to be Frenkel-like. The diffusion length of this exciton is 225 ± 15 nm, compared to 88 ± 6 nm for excitons generated between 475 and 555 nm.