Strain-Enhanced Formation of Delocalized Exciton States in Phthalocyanine Crystalline Thin Films

The formation of delocalized excitonic states in organic semiconductors is highly desirable because it leads to efficient energy transport in devices. We investigate the potential of uniaxial strain as a tuning dial for delocalized excitons (i.e., exciton-polarons) in crystalline thin films of soluble octabutoxy phthalocyanine. Absorption and photoluminescence spectra confirm the formation of delocalized excitonic states in the presence of tensile strain, accompanied by a red shift of low-frequency vibration modes (<100 cm(-1)) in Raman spectroscopy, which are likely responsible for the delocalized exciton formation. Remarkably, an 80% enhancement in photoluminescence intensity and a 30 nm red shift in peak wavelength are observed for a tensile strain of 4.9%, which is equivalent to a temperature reduction approximately by 100 K below room temperature. These results show promise that strain engineering can efficiently modify the exciton-phonon coupling in octabutoxy phthalocyanine crystalline thin films toward enabling delocalization at room temperature.

Automated summary

This research investigates the potential of strain engineering in promoting the formation of delocalized excitonic states in organic semiconductors. The results demonstrate that tensile strain leads to the formation of delocalized excitons, accompanied by enhanced photoluminescence intensity and red shift in peak wavelength. These findings offer promising prospects for achieving delocalization at room temperature through strain engineering.