Mechanical strain, thermal and pressure effects on the absorption edge of an organic charge-transfer polymer for flexible photovoltaics and sensors

Abstract

Mechanical and thermal strains in organic photovoltaic layers deposited on poly(ethylene terephthalate) (PET) and glass substrates and the resulting effect on the bandgap energy have been determined for the organic charge-transfer polymer PTB7. Its strong bathochromic shift of the absorption spectra under pressure also depends on the layer preparation method. The effects of different solvents and PTB7 concentrations on agglomerate formation were also studied. A perfect linear dependence of the concentration vs. absorbance was observed up to 1.81 × 10⁻⁷ M for chlorobenzene or o-dichlorobenzene solution. The thermal image monitoring of the current response at an increasing potential showed a linear current-to-voltage tendency, indicating that the conductive behaviour of the polymer depends on the substrate used in PET/ITO/PTB7/Ag/ITO/PET and glass/ITO/PTB7/Ag/ITO/glass devices. The PTB7 layer on the PET/ITO substrate displays superior mechanical properties suitable for flexible photovoltaic panels exposed to strain and deformations.