Tailoring optical properties and stimulated emission in nanostructured polythiophene

Alberto Portone,Rodrigo Ramos,Federico Branchi,Marília J Caldas,Elisa Molinari,Luana Persano,Giulio Cerullo,Lucia Ganzer,Dario Pisignano,Tersilla Virgili,Deborah Prezzi

doi:10.1038/s41598-019-43719-0

Abstract

Polythiophenes are the most widely utilized semiconducting polymers in organic electronics, but they are scarcely exploited in photonics due to their high photo-induced absorption caused by interchain polaron pairs, which prevents the establishment of a window of net optical gain. Here we study the photophysics of poly(3-hexylthiophene) configured with different degrees of supramolecular ordering, spin-coated thin films and templated nanowires, and find marked differences in their optical properties. Transient absorption measurements evidence a partially-polarized stimulated emission band in the nanowire samples, in contrast with the photo-induced absorption band observed in spin-coated thin films. In combination with theoretical modeling, our experimental results reveal the origin of the primary photoexcitations dominating the dynamics for different supramolecular ordering, with singlet excitons in the nanostructured samples superseding the presence of polaron pairs, which are present in the disordered films. Our approach demonstrates a viable strategy to direct optical properties through structural control, and the observation of optical gain opens the possibility to the use of polythiophene nanostructures as building blocks of organic optical amplifiers and active photonic devices.

Highlights

Conjugated polymers comprise a broad class of organic materials that have attracted a great deal of attention in the last decades due to their fundamental properties and applications in innovative optoelectronic devices[1,2,3,4]
We suggest a rationale for this difference: in ordered systems, individual polymers can be approximated as straight chains, with one-electron orbitals that extend over the whole chain
The stamp is removed and NWs are imaged by confocal microscopy (Fig. 1b), scanning electron microscopy (SEM) (Fig. 1c) and atomic force microscopy (AFM) (Fig. 1d–f)

Summary

Introduction

Conjugated polymers comprise a broad class of organic materials that have attracted a great deal of attention in the last decades due to their fundamental properties and applications in innovative optoelectronic devices[1,2,3,4]. Their flexibility, easy processability and light weight together with good charge-carrier mobilities (up to a few cm2V/s) enable the production of large-area, bendable or stretchable optical and electronic components via low-cost solution processing. In spite of the proven beneficial effects of highly-ordered organic nanostructures on polythiophene electronic components, little is known on their influence on the optical response[31,32]

Methods

Results

Conclusion