Polymeric Thin Films for Organic Electronics: Properties and Adaptive Structures.

Sebastiano Cataldo,Bruno Pignataro

doi:10.3390/ma6031159

Abstract

This review deals with the correlation between morphology, structure and performance of organic electronic devices including thin film transistors and solar cells. In particular, we report on solution processed devices going into the role of the 3D supramolecular organization in determining their electronic properties. A selection of case studies from recent literature are reviewed, relying on solution methods for organic thin-film deposition which allow fine control of the supramolecular aggregation of polymers confined at surfaces in nanoscopic layers. A special focus is given to issues exploiting morphological structures stemming from the intrinsic polymeric dynamic adaptation under non-equilibrium conditions.

Highlights

The discovery in 1976 by Heeger, MacDiarmid and Shirakawa [1,2] of conductive polymers opened a new field of research at the boundary between chemistry and the physics of condensed matter
This review focuses on the role of the thin-film morphology in organic thin film field-effect transistors (OFETs) and organic solar cells (OSCs)
There is no consolidated theoretical framework to predict and explain the non-equilibrium structures of thin films and experimentalists usually work by trial and error procedures to optimize the structures frozen in the confined layers of single polymers or blends over suitable substrates

Summary

Introduction

The discovery in 1976 by Heeger, MacDiarmid and Shirakawa [1,2] of conductive polymers opened a new field of research at the boundary between chemistry and the physics of condensed matter. Thermodynamic self-processes are quite easy to develop and lead to a relatively simple organization, whereas the non-equilibrium ones are characterized by structural fluctuations allowing even ordered geometries like periodic super-structures or supra-molecular aggregates [21] By freezing these complex structures on a given substrate, it is possible to make an artificial selection among infinite energy levels (in principle) corresponding to as many thin-film organization paths [22]. An ordered structure may be frozen on a surface by acting on the kinetic parameters of the deposition process (as solvent evaporation rate, film-transfer speed etc.) which in turn bias the competing forces involved in the structural evolution (intermolecular and surface-molecule electromagnetic forces, chemical potential gradients etc.) [26] These competing forces arise from the chemical nature of the building-blocks (chemical pressure) and from the physical parameters of the process (physical pressure), that have to be conveniently balanced to achieve the desired nanostructures. It aims to show the relation between molecular 3D order and device performance, reporting some significant case studies from the most recent literature, which encompasses some of the principal solution methods for organic thin-film deposition and structural manipulation

Organic Field Effect Transistors

Organic Solar Cells

Findings

Conclusions