Advancing stretchable optoelectronic devices with structural and material designs
Date of Issue2016
School of Materials Science and Engineering
Stretchable electronics are emerging as a new type of devices with their exceeding mechanical compliance compared to the rigid or flexible devices. They can confront demanding mechanical deformations such as twisting, stretching, or conformably wrapping, enabling electronic applications under rigorous mechanical conditions that cannot be addressed by conventional devices. Stretchable electronics are believed to be one of the essential technologies for the next generation electronic device applications. With their significantly improved mechanical “robustness”, the challenges to develop the enabling technologies for stretchable devices also become more difficult to resolve. In this thesis, we focus on developing new structural and material approaches to enable stretchable optoelectronic devices, including stretchable photodetectors and stretchable electroluminescent devices. Nanowires have driven special interest in the research society due to their unique one-dimensional structure. We presented the fabrication of Zn2GeO4 nanowires and Zn2SnO4 nanowires in a chemical vapor deposition system and their assembly by a solution-processible approach for highly deformable and transparent ultraviolet photodetectors. The solution-processible approach was firstly demonstrated to assemble Zn2GeO4 nanowires and silver nanowires for transparent and flexible photodetectors. The fabricated device showed excellent mechanical stability, high photoresponse and fast switching time. Mechanical properties of the nanowire network structures were further improved to achieve stretchable devices. The first stretchable and transparent ultraviolet photodetector was demonstrated by embedding the nanowire device structures into polymer matrix. Zonyl surfactant was found to be an efficient additive to improve the bonding strength between the nanowire networks and the stretchable polymer matrix, leading to significantly improved transfer efficiency. The transparent and stretchable silver nanowire networks embedded in polymer matrix were also exploited as the electrodes for stretchable alternating-current electroluminescent (ACEL) devices. The highly stretchable EL devices fabricated with ACEL materials could achieve stable emission under large stretching strains. The unique emission mechanism in ACEL materials was essential for stable device operation under mechanical deformations. With the simple device configuration and highly conformable structures, the stretchable ACEL devices were integrated with dielectric elastomer actuators. An unprecedented self-deformable EL device was demonstrated which could be driven into dynamic shapes under external electrical bias. Stretchability of the ACEL devices was further improved by using ionic conductors as the transparent and stretchable electrodes. The ionic conductors were fabricated with blends of conductive electrolytes and polymers. Transparency and stretchability of the ionic conductors greatly exceeded those of the electronic conductors. An extremely stretchable ACEL device using ionic conductors as the stretchable and transparent electrodes was demonstrated with the stretchability of 700%.