Strain-Induced Optical and Molecular Transformations in PET Films for Organic Electronic Applications

TL;DR

This paper investigates how mechanical strain affects the optical and molecular properties of PET films, revealing significant changes in transparency and molecular structure that impact their use in flexible electronic devices.

Contribution

It provides new insights into the strain-induced optical and structural transformations in PET, crucial for enhancing performance in flexible electronics.

Findings

Strain increases UV-Vis absorption in PET by up to 100%.

Vibrational modes shift irreversibly beyond 5% strain, indicating molecular reorganization.

The C-O stretching mode is highly responsive to applied stress.

Abstract

Poly(ethylene terephthalate) (PET) films are widely used in flexible electronics and optoelectronics, where their mechanical durability and optical performance under strain are essential for device reliability. This study investigates the impact of applied mechanical strain on the optical and molecular properties of PET at room temperature,using UV-Vis absorption and Raman spectroscopy. The work explores how varying strain levels, from 0% (unstretched) to 30%, affect the transparency, vibrational modes, and molecular reorganization within PET films. UV-Vis absorbance measurements reveal that strain induces significant changes in the light transmission properties of PET, particularly in the visible range, and increases absorption in the UVA and visible region by up to 100%. Raman spectra indicate that strain levels higher than 5% lead to irreversible shifts of vibrational lines, accompanied by an increase of their full width at half maximum (FWHM), suggesting molecular reorientation and crystallinity changes. The phonon mode coupled with C-O stretching [O-CH2] shows the strongest response to applied mechanical stress. This study provides a comprehensive understanding of strain-induced optical and structural alterations in PET, with implications for improving the mechanical and optical performance of PET-based devices in strainsensitive applications, such as organic solar cells (OSCs), organic light-emitting diodes (OLEDs), and flexible sensors.