Continuous-Flow Direct Writing of Hybrid TiO 2 Flexible Photo-Electrodes: Processing, Microstructure and Functionality I
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Continuous-Flow Direct Writing of Hybrid TiO2 Flexible Photo-Electrodes: Processing, Microstructure and Functionality Interrelations Maria A. Torres Arango1, Domenic T. Cipollone1, Lynnora O. Grant1, Dimitris Korakakis2 and Konstantinos A. Sierros1* 1
FEST Flexible Electronics for Sustainable Technologies Laboratory, West Virginia University, 395 Evansdale Drive, Morgantown, WV 26506, USA 2
Material Growth and Characterization Lab, West Virginia University, Lane Department of Computer Science and Electrical Engineering, 395 Evansdale Drive, Morgantown, WV, 26506, USA *Corresponding author: [email protected]
ABSTRACT Flexible electronics manufacturing from functional inks is a versatile approach gaining interest from both industry and academia at an accelerated pace; towards its full development, research studies establishing connections between the inks processing conditions and final materials functionalities become necessary. In this work, we report on the relations between synthesis, continuous - flow direct writing parameters, and low energy intensity post-processing of functional TiO2 hybrid ink patterns. Such inks are printed on heat sensitive polymer substrates with typical application in dye solar cell photoelectrodes; nevertheless, their versatility spans a wide range of other applications from sensors to photocatalysts. For the ink formulation, we use an initial crystalline nanoparticle TiO2 phase that provides the main functionality of the printed films. We also add a Ti-precursor that, when post-treated, provides connecting paths for the initial phase thus forming continuous porous structures. We find that the ink’s formulation plays a pivotal role by providing the means for tuning its rheological properties (necessary for successful direct writing), the ink-substrate interactions, and the printed microstructures. We further discuss the implications of such compositional variations, introduced when adding polymeric agents, such as polyacrylic acid, on the crystallization of the Ti-organic precursor into TiO2 bridges between the nanoparticles. We finally report on the electrical properties of the printed TiO2 photoelectrodes as compared to conventionally fabricated counterparts. The design, continuous – flow direct writing, and the subsequent mild thermal-energy treatments of hybrid sol-gel based TiO2 inks may hold the key for large-scale and sustainable additive manufacturing of flexible functional components for a range of applications.
INTRODUCTION There is currently a burgeoning interest to study new ink formulations and additive manufacturing methods for the next generation of flexible devices used in energy applications[1], [2]. Although the continuous – flow direct writing process has been introduced more than a decade ago[3], it has recently re-emerged as a promising enabler of exciting energy
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