Advanced Materials

Theodorus van de Ven, Armand Soldera, Theodorus van de Ven, Armand Soldera

• Publisher: De Gruyter
• Year: 2020
• ISBN:
  9783110537796
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Advanced Materials gives an unique insight into the specialized materials that are required to run our modern society. Provided within are the fundamental theories and applications of advanced materials for metals, glasses, polymers, composites, and nanomaterials. This book is ideal for scientists and engineers of materials science, chemistry, physics, and engineering, and students of these disciplines.

1 Design Principles for Organic Semiconductors

Julia A. Schneider

Department of Chemistry, Fordham University, NY

Dmitrii F. Perepichka

Department of Chemistry, McGill University, Québec

Abstract

Designing organic semiconductors--whether polymers or small molecules--involves a myriad of synthetic choices. Every choice, from incorporating heteroatoms to substituents, effects the optoelectronic properties of the material, its morphology, and its ultimate device performance. This chapter presents the reader with current design strategies and known structure-property relationships. For context, this chapter also briefly discusses the history of the field, theories of charge transport, device applications, and concludes with a selection of reported organic semiconductors.

Keywords: organic electronics, organic semiconductor, photovoltaics, conjugated polymer, donor-acceptor, morphology, charge transport

1.1 Introduction

Organic electronics encompass devices in which molecules or polymers serve as the electrically active material. Notably, the properties of these organic materials can be endlessly tuned through structural modifications. The ability to tailor a semiconductor for a specific application is one of the most attractive aspects of organic electronics. Additionally, solution-processable materials offer the possibility of inexpensive, large area devices, via, for example, roll-to-roll or inkjet printing. Solar cells produced in this way could potentially satisfy the world’s increasing energy demands in a sustainable manner. Organic electronics made entirely from biodegradable materials would help stem the accumulation of e-waste in landfills. For organic electronics to become widely adopted and compete with the existing inorganic materials, however, they need to demonstrate sufficiently long lifetimes and competitive optoelectronic properties. Since the 1970s, this has fueled a continuing quest for new high-performance, stable materials, as well as extensive research into what factors dictate charge transport and how to control them. The goal of this chapter is to contribute new design strategies for the synthesis of organic semiconductors (OSCs) and to better our understanding of structure–property relationships.

While some design strategies yield predictable results, many structure–property relationships are still not well understood, especially as they relate to supramolecular ordering. In the last three decades, a multitude of OSCs have been synthesized, primarily by trial and error, with a material’s solid-state packing and associated device performance only discussed after the fact. This chapter will introduce the reader to a number of electronically active molecules and polymers and will discuss the design strategies used to achieve certain characteristics. These design strategies will then be discussed in terms supramolecular ordering.

This chapter will cover four main topics: (1) the history of organic electronics, discussing the theories of charge transport, and devices that employ OSCs; (2) design principles for the synthesis of OSCs, along with an exemplifying case study; (3) design strategies specifically geared to supramolecular ordering; and (4) a review of representative reported OSCs that illustrate the current state of the field.

1.2 History of OSCs

Semiconductors are ubiquitous in modern technology: they can be found in the transistors and diodes that all our electronic devices use. The first transistor device was invented in 1947 while Bardeen, Brattain, and Shockley were studying surface states in a germanium crystal. Ever since, inorganic materials like silicon or gallium arsenide have been predominantly used in our electronic components. Conductive organic materials, however, had already been discovered, although perhaps unbeknownst to the discoverer. In 1862, Letheby observed conductive and electrochromic behavior in a unidentified “dirty blueish-black powder,” now thought to be polya...