Название: Defects in Organic Semiconductors and Devices
Автор: Thien-Phap Nguyen
Издательство: Wiley-ISTE
Год: 2023
Страниц: 279
Язык: английский
Формат: pdf (true), epub
Размер: 10.1 MB

Defects play a key role in the physical properties of semiconductors and devices, and their identification is essential in assessing the reliability of electronic devices.

Defects in Organic Semiconductors and Devices introduces the fundamental aspects of defects in organic semiconductors and devices in relation to the structure of materials and architecture of electronic components. It covers the topics of defect formation and evolution, defect measurement techniques and their adaption to organic devices, the effects of defects on the physical properties of materials and their effects on the performance and lifetime of organic devices. Identifying defects and determining their characteristics in the structure of organic devices such as OLEDs, OFETs and OPVs make it possible to better understand degradation processes and develop solutions to improve the reliability of such devices.

Conventional semiconductors such as silicon and germanium are crystalline solids, where the atoms form a periodic arrangement. This ordered structure provides highly interesting electrical and optical properties to the semiconductors that are used to build electronic components and devices. Since the invention of transistors, myriad applications have been achieved in the field of electronics, bringing great comfort to everyday life: TVs, lighting, computers and cell phones, to name but a few. However, as stated by Victor Hugo, “On voit les qualités de loin et les défauts de près” (we see qualities at a distance and defects at close range), despite their remarkable and numerous qualities, it was very quickly observed that many of the first electronic devices manufactured using conventional semiconductors malfunctioned, despite careful control of the processing. Through investigations of the defective parts, it was found and later proved that, irrespective of the particular devices, the nature of the materials played a primary role in the reliability of the electronic products, whose yield is closely linked to the presence of defects.

As perfect materials do not exist, the properties of conventional semiconductors are affected by defects which interrupt the crystalline pattern. Common types of defects include point defects (impurities, interstitials, vacancies, etc.), dislocations, and grain boundaries can be formed during the processing but can also be intentionally (doping) or unintentionally (contamination, degradation) incorporated in the prepared materials. In the doping process, impurities are intentionally introduced to materials in order to modify and control the conduction of the semiconductors by adding energy states in a band gap, which provide charge carriers to the conduction or valence bands. These defects have a beneficial effect on the electrical properties of the materials. In most other cases, defects have negative or detrimental effects on the properties and functionalities of materials by enhancing the disorder, impeding the charge transport and affecting the overall physical processes in the semiconductors. As defects are unavoidable, it is necessary to acquire accurate knowledge of their origin and their effects in order to efficiently control and eventually eliminate them. Investigations of defects in conventional semiconductors have been intensively developed with well-established and elaborated measurement techniques in order to determine the defect parameters in materials and devices, improving the knowledge of their origin and their effects on the performance of the devices studied. At the same time, diverse physical models on the material structure, energetic distribution and charge carrier kinetics have been proposed and successfully applied in order to elucidate defect measurement results in most conventional semiconductors.

Structurally speaking, organic semiconductors differ from conventional semiconductors. Since there is no defined orientation and order of molecules that make up the organic matter, they can be classified as amorphous materials. The lack of orientational order combined with the weak van der Waals bonding forces make the organic materials likely to form defects, which can be explained by the small amount of energy needed to displace the molecule from its equilibrium position. Indeed, similarly to inorganic semiconductors, impurities and structural defects such as point defects, dislocations and grain boundaries can be formed or introduced to the organic semiconductors during the synthesis and the processing of materials. Due to their nature and chemical structure, they are also more sensitive than their inorganic counterparts to contact with environmental media. The structural changes due to the interactions between the organic material and the environment often lead to the formation of defects in the contact region. From this consideration, we can expect defects in organic materials to be investigated by applying similar methodology and techniques as in conventional semiconductors. To take the specific properties of the organic materials into account, further advanced measurement techniques and methodology approaches need to be used and developed, and the results obtained must be effectively analyzed and used. This book aims to provide a comprehensive introduction on the defects and degradation of semiconductors used in electronic organic devices.

This book is intended for researchers and students in university programs or engineering schools who are specializing in electronics, energy and materials.