Photoconduction in Polydiacetylene Multilayer Structures and Single Crystals. Evidence for Band‐to‐Band Excitation

Abstract

Abstract Steady state photoconduction action spectra for polydiacetylene multilayer structures and single crystals (TCDU) are reported. Interpretation is given in terms of a valence‐to‐conduction band transition which is buried under the vibronic sidebands of the dominant exciton transition. The associated absorption coefficient follows a (α b ħω) ˜ (ħω − E g ) 2 law which indicates either an indirect transition or a direct transition between non‐parabolic bands. The general validity of this relationship is supported by literature data for PTS, DCHD, and polyethylene. Gap energies are (2.5 ± 0.1) eV and (2.6 ± 0.1) eV for two different multilayer forms, (2.6 ± 0.1) eV for TCDU, (2.1 ± 0.1) eV for PTS, and (2.30 ± 0.05) eV for DCHD. The transition is three‐dimensional indicating finite valence and conduction band dispersion perpendicular to the polymer chain direction.