Inorganic Flexible Optoelectronics

Materials and Applications

Zhenqiang Ma, Dong Liu

• Publisher: Wiley-VCH
• Year: 2019
• Print ISBN:
  9783527343959
• Edition: 1
• eBook ISBN:
  9783527812981
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Comprehensively covering inorganic flexible optoelectronics and their applications

This highly application-oriented book provides an overview of the vibrant research field of inorganic flexible optoelectronics ? from materials to applications ? covering bulk materials as well as nanowires, thin films, nanomembranes for application in light emitting diodes, photodetectors, phototransistors, and solar cells.

Edited and written by world-leading experts in the field, Inorganic Flexible Optoelectronics: Materials and Applications begins by covering flexible inorganic light emitting diodes enabled by new materials and designs, and provides examples of their use in neuroscience research. It then looks at flexible light-emitting diodes based on inorganic semiconductor nanostructures ? from thin films to nanowires. Next, the book examines flexible photodetectors with nanomembranes and nanowires; 2-D material based photodetectors on flexible substrates; and IV group materials based solar cells and their flexible photovoltaic technologies. Following that, it presents readers with a section on thin-film III-V single junction and multijunction solar cells and demonstrates their integration onto heterogeneous substrates. Finally, the book finishes with in-depth coverage of novel materials based flexible solar cells.

-A must-have book that provides an unprecedented overview of the state of the art in flexible optoelectronics
-Supplies in-depth information for new and already active researchers in the field of optoelectronics
-Lays down the undiluted knowledge on inorganic flexible optoelectronics ? from materials to devices
-Focuses on materials and devices for high-performance applications such as light-emitting diodes, solar cells, and photodetectors

Inorganic Flexible Optoelectronics: Materials and Applications appeals to materials scientists, electronics engineers, electrical engineers, inorganic chemists, and solid state physicists.

1
Flexible Inorganic Light Emitting Diodes Enabled by New Materials and Designs, With Examples of Their Use in Neuroscience Research

Hao Zhang¹, Philipp Gutruf², and John A. Rogers³

¹ Northwestern University, Department of Materials Science and Engineering, 2145 Sheridan Road, Evanston, IL, 60208, USA

² University of Arizona Tucson, Department of Biomedical Engineering, 1230 N Cherry Ave., Tucson, AZ 85719, USA

³ Northwestern University, Simpson Querrey Institute for Nano/Biotechnology, Center for Bio‐integrated Electronics, Departments of Materials Science and Engineering, Biomedical Engineering, Chemistry, Mechanical Engineering, Electrical Engineering and Computer Science, Civil and Environmental Engineering, 2145 Sheridan Road, Evanston, IL, 60208, USA

1.1 Introduction

Light emitting diodes (LEDs) representessential components in nearly all solid‐state lighting systems. Although conventional LEDs formed from epitaxial materials grown on rigid, brittle, and planar substrates are the most dominant technology, flexible LEDs continue to be of great interest, originating primarily from concepts in flexible, paper‐like displays from the 1990s [1]. Flexible LEDs, as defined by their ability to be bent, twisted, and deformed in other ways, also serve as the basis for advanced optoelectronic technologies, ranging from next‐generation displays in large or portable formats to wearable/implantable devices capable of intimate contact with soft, curvilinear bio‐interfaces. Organic materials, including polymers and small molecules, are natural choices for flexible LEDs due to their favorable mechanical properties, their ability to provide multicolor light emission in ultrathin, lightweight films, and their low‐temperature processability and associated compatibility with plastic substrates [1]. Challenges in performance degradation from photooxidation and other subtle effects and their limited color purity remain as key hurdles for organic light emitting diodes (OLEDs). By contrast, LEDs that exploit inorganic semiconductor materials as emissive layers outperform their organic counterparts in terms of brightness, lifetime, efficiency, and color purity. Recent progress in materials designs, fabrication concepts, and assembly approaches now enable high‐performance, flexible classes of inorganic light emitting diodes (ILEDs). Integrating these ultrathin components with flexible electronics establishes the basis for system‐level, advanced systems for deformable, high‐brightness displays and for biomedical tools that provide diagnostic/therapeutic capabilities. The two main approaches toward flexible ILEDs use (i) microscale ILEDs fabricated from high‐quality epitaxial materials grown on source wafers, subsequently released and assembledon flexible target substrates using the techniques of transfer printing, and bridged by structurally optimized interconnects (Section 1.2); and (ii) ILEDs formed with emissive layers composed of solution‐processed semiconductors and/or low‐dimensional nanomaterials. The former approach mainly relies on processing of well‐established, high‐performance III–V semiconductors with a novel set of techniques, while the latter deploys diverse classes of new materials, including colloidal semiconductor nanocrystals (or quantum dots [QDs], see Section 1.3), metal halide perovskites (Section 1.4), and two‐dimensional (2D) materials (Section 1.5).

This chaptersummarizes the most recent advances and key remaining challenges associated with flexible ILEDs from both the materials and device perspectives. The focus is on their unique properties as candidates in flexible ILEDs and state‐of‐the‐art devices design and performance. In addition, recent progress in integrating flexible ILEDs into system‐level optoelectronic platforms for various applications highlights the current state of the field. The use of miniaturized, flexible ILEDs to optogenetically modulate neural activity (described in Section 1.6) represents one of the most recent cases.

1.2 Flexible Micro‐Inorganic LEDs (μ‐ILEDs)

A combination of properties such as brightness, efficiency, color purity, and lifetime makes III–V semiconductor‐based LEDs the most attractive candidates for solid‐state lighting applications compared to almost all other options, including OLEDs [2,3]. Existing techniques to incorporate commercial ILEDs into systems such as billboard‐scale displays involve robotic, pick‐and‐place assembly of ILEDs diced from a wafer source, followed by device‐by‐device, (sub)millimeter‐scale packaging, and interconnecting of these components with a collection of bulk wires and heat sinks [4]. These conceptually old techniques are ineffective for assembling ultrasmall (<200 μm × 200 μm, microscale), ultrathin (<50 μm) μ‐ILEDs into dense, highly pixelated arrays, particularly on flexible substrates. A set of unconventional processes, starting with the rational design of the μ‐ILEDs in released configurations but still tethered to the underlying growth wafer, followed by transfer printing to a target substrate, circumvents the abovementioned restrictions [5–9]. This sort of deterministic assembly approach enables the use of μ‐ILEDs in a wide range of applications, from high‐resolution flexible/deformable displays to cellular‐scale biocompatible lighting sources for sensing, therapy, and neuroscience research [4 10–21]. This section focuses on recent developments in μ‐ILEDs, including the materials design and fabrication concepts, as well as their unconventional implementation at circuit and system levels.

The first demonstrations of flexible assembly of μ‐ILEDs involved red‐emitting AlInGaP epitaxial structures. [4]The active layers include emissive quantum wells (6 nm thick In_0.56Ga_0.44P wells, with 6 nm thick barriers of...

Table of contents

• Cover
• Table of Contents
• Preface
• 1 Flexible Inorganic Light Emitting Diodes Enabled by New Materials and Designs, With Examples of Their Use in Neuroscience Research
• 2 Flexible Light‐Emitting Diodes Based on Inorganic Semiconductor Nanostructures: From Thin Films to Nanowires
• 3 Flexible Photodetectors with Nanomembranes and Nanowires
• 4 2‐D Material‐Based Photodetectors on Flexible Substrates
• 5 IV Group Materials‐Based Solar Cells and Their Flexible Photovoltaic Technologies
• 6 Thin‐Film III–V Single Junction and Multijunction Solar Cells and Their Integration onto Heterogeneous Substrates
• 7 Novel Materials‐Based Flexible Solar Cells
• Index
• End User License Agreement