# Excitonic coupling dominates the homogeneous photoluminescence excitation linewidth in semicrystalline polymeric semiconductors

## TL;DR

This study measures the homogeneous excitation linewidth in a semicrystalline polymer semiconductor, revealing excitonic coupling as a dominant factor influencing linewidth broadening at low temperatures.

## Contribution

It introduces a two-dimensional coherent photoluminescence excitation spectroscopy method to quantify linewidths in polymer semiconductors, highlighting the role of excitonic interactions.

## Key findings

- Linewidth always exceeds 110 meV at 8 K
- Linewidth shows spectral dependence, minimal near the 0-0 peak
- Excitonic coupling significantly influences linewidth broadening

## Abstract

We measure the homogeneous excitation linewidth of regioregular poly(3-hexylthiophene), a model semicrystalline polymeric semiconductor, by means of two-dimensional coherent photoluminescence excitation spectroscopy. At a temperature of 8\,K, we find a linewidth that is always $\gtrsim 110$\,meV full-width-at-half-maximum, which is a significant fraction of the total linewidth. It displays a spectral dependence and is minimum near the 0--0 origin peak. We interpret this spectral dependence of the homogeneous excitation linewidth within the context of a weakly coupled aggregate model.