Department of Energy EngineeringFlexible transparent electrode is an essential component for several kinds of electronic and optoelectronic applications, such as organic solar cells (OSCs), perovskite solar cells (PSCs), organic light-emitting diodes (OLEDs), touch sensors, and electronic skins (E-skins). Although conventional indium tin oxide (ITO) has been widely used in commercial transparent electrodes, it still shows a limitation in the fabrication of flexible transparent electrodes for applications in flexible/wearable electronic devices because of their inherent brittleness. Among various alternatives of ITO, silver nanowire (AgNW) network has been considered as promising conductive nano-material due to their high electrical conductivity, excellent transmittance, and mechanical flexibility that can be readily deposited by cost-effective and large-scale solution process. However, random AgNW networks prepared by solution processing have several drawbacks, such as high junction resistance between nanowires (NWs), low transmittance, haze issues, and rough surface morphologies, resulting in a degradation of the device performance. Electrical and optical properties of random AgNW networks can be strongly affected by controlling NW density, electrical current path, and junction resistance related to conductive percolated networks. Therefore, manipulating the assembled structure of AgNW network can provide powerful platforms to realize ideal flexible transparent electrodes with high electrical conductivity, superior transmittance, and smooth surface morphologies for achieving high-performance electronic and optoelectronic device.
In this thesis, we introduce aligned AgNW transparent electrodes and their applications in flexible optoelectronic and functional electronic devices. Firstly, Chapter 1 introduces the research tends in transparent electrodes and several issues of AgNW networks that should be carefully considered in the fabrication for their potential device applications. In chapter 2, we demonstrate the capillary printing technique to make highly aligned AgNW network to fabricate high-performance transparent electrodes for improving device efficiency of optoelectronic devices including OSCs and OLEDs. In Chapter 3, we demonstrate the fabrication of nanoparticle (NP)-enhanced plasmonic AgNW electrode for high-performance optoelectronic devices in which the NP-NW hybrid plasmonic system generates gap plasmonic coupling which induces a large electric field enhancement, resulting in an improvement of the device efficiency in both OSC and OLED devices. In Chapter 4, we demonstrate the fabrication of ultrathin and flexible perovskite solar cell foils with orthogonal AgNW electrodes, which exhibits high power-per-weight performance as well as a conformal contact capability to curvilinear surface. In Chapter 5, we introduce a large-scale assembly technique to uniformly align AgNW arrays for the fabrication of large area transparent electrodes, where cross-aligned AgNW network shows better electrical and optical properties as well as large-scale uniformity than random AgNW network. For the proof of the concept demonstration, we fabricated a flexible force-sensitive touch screen panel integrated with a mechanochromic polymer film. Finally, we introduce a transparent and conductive nano-membrane (NM) incorporated with orthogonal AgNW arrays in Chapter 6, which exhibits enhanced electrical and mechanical properties than pure polymeric NMs. To show the unique properties of these hybrid NMs for potential device applications, we demonstrate skin-attachable thermoacoustic-based NM loudspeaker and wearable NM microphone, both of which show much improved device performances compared to conventional thin film-based devices.
In this thesis, studies on aligned AgNW transparent electrodes and their device applications could be further expanded for diverse flexible and wearable optoelectronic and electronic applications, such as conformal wearable sensors, healthcare monitoring devices, and wearable plasmonic devices.clos
