The light-induced localized trap state density of states in organic bulk heterojunction solar cells is reported, based on capacitance-frequency and photocurrent spectroscopy measurements. Several different cell materials show qualitatively the same behavior. A deep trap is induced by prolonged white light illumination with state density of 1016-1017 cm-3 and is observed by both experimental techniques. The trap depth is 0.5-0.7 eV. The light soaking has no measurable effect on the localized band tail density of states. The observation of the effect in many materials is consistent with the model that traps are created by light-induced dissociation of C-H bonds. The data suggests that disorder enhances the trap creation. The data also allow an estimate of the trap capture cross section, which is discussed in terms of local transport anisotropy.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films