Transient strain induced electronic structure modulation in a semiconducting polymer imaged by scanning ultrafast electron microscopy

TL;DR

This study uses scanning ultrafast electron microscopy to visualize how transient, photo-induced strain dynamically modulates the electronic structure of a semiconducting polymer, revealing potential for opto-electronic property tuning.

Contribution

It demonstrates the capability of SUEM to image and analyze local transient strain effects on electronic structures in polymers at high spatio-temporal resolution.

Findings

Photo-induced strain causes a ring-shaped contrast in SUEM images.

Contrast rise time is approximately 300 ps.

Electronic structure modulation is supported by finite-element analysis.

Abstract

Understanding the opto-electronic properties of semiconducting polymers under external strain is essential for their applications in flexible opto-electronic, light-emitting and photovoltaic devices. While prior studies have highlighted the impact of static strains applied on a macroscopic length scale, assessing the effect of a local transient deformation before structural relaxation occurs is challenging due to the required high spatio-temporal resolution. Here, we employ scanning ultrafast electron microscopy (SUEM) to image the dynamical effect of a photo-induced transient strain in the archetypal semiconducting polymer poly(3-hexylthiophene) (P3HT). We observe that the photo-induced SUEM contrast, corresponding to the local change of secondary electron emission, exhibits a ring-shaped spatial profile with a rise time of $\sim 300$ ps, beyond which the profile persists in the absence of a spatial diffusion. We attribute the observation to the electronic structure modulation of P3HT caused by a photo-induced strain field owing to its relatively low modulus and strong electron-lattice coupling, as supported by a finite-element analysis. Our work provides insights into tailoring opto-electronic properties using transient mechanical deformation in semiconducting polymers, and demonstrates the versatility of SUEM to study photo-physical processes in diverse materials.