The shift of the open-circuit voltage (Voc) of flexible organic solar cells (OSCs) under bending conditions was investigated by fabricating bi-layer heterojunction and polymer-based OSCs on flexible polyethylene terephthalate (PET) substrates. To realize the performance variations of flexible solar cells characterized by important parameters, Vocwas measured when the substrate was bent under various curvatures. The Vocwas increased and decreased by using tensile and compressive stresses, respectively. The ratio of increase for Vocis larger than the ratio of reduction, thus indicating that the intermolecular distance of an organic semiconductor is difficult to change because of the strong electrostatic repulsive force. A quantitative analysis of energy levels by the photoluminescence spectrum, UV-visible absorption spectrum, and quantum chemical calculation at various bending states was used to explain the Vocas a function of bending curvature. The peak shifts of UV-visible absorption and photoluminescence spectra provide direct evidence of the variation in energy levels when devices are bent, which causes Vocshifts. For bent organic semiconductor films, the bending curvature-dependent intermolecular distance was studied by Raman spectroscopy by analyzing the intermolecular coupling energy. This study shows that the change of Voccannot be neglected in the application of flexible OSCs on a flexible loading circuit.
All Science Journal Classification (ASJC) codes
- Renewable Energy, Sustainability and the Environment
- Materials Science(all)