Optoelectronic properties and photonic-based processing of printed conductive thin-film architectures

Abstract

The developing field of hybrid printed electronics promises a suitable replacement for many traditional silicon-based technologies by lowering manufacturing costs and increasing production speed, while offering similar performance. To realize this, novel approaches of additive manufacturing and processing of devices are required, aiming to meet industrial requirements such as high electrical conductivity, optical transmittance, long device lifetime. This doctorate thesis demonstrates various applications of nanomaterials processing of atop different substrates, including direct laser and photonic sintering, to produce optoelectronic devices and aimed to obtain reliable and reproducible results. To do this, a literature review is presented where the principles of photonic processing are explained, followed by an overview of the up-to-date processing techniques and optoelectronics device applications. After, a description of the role of metal-oxides and metallic nanostructures in optoelectronics, with emphasis on processing of TiO2 and silver nanowires. Following the literature review, large-area, on-demand crystallization of TiO2 thin films are presented using a low-cost, of-the-shelf 405 nm laser source. This application of direct laser processing shows the optimization process to achieve single or hybrid films of anatase or rutile TiO2, that are produced at room conditions, without the need of additional equipment. After, transparent conductive electrodes made of silver nanowires are processed using photonic sintering with state-of-the-art processing equipment. This project compares their optical-to-electrical figures of merit with those of films fabricated using traditional thermal methods. A new figure of merit metric is proposed to correlate the effects of the processing pulse fluence and the final sheet resistance of the films. Lastly, a multi-material ensemble made of silver nanowires and TiO2 is processed using two independent photonic sintering steps, done on a heat-sensitive, flexible substrate. The results show how different materials can be processed using the same photonic sintering machine by taking advantage of their divergent physical qualities. Metallic nanostructures benefit from short-pulse, high peak power density conditions and, photo-sensitive metal-oxides respond to long-pulse, low peak power density processing conditions. This multi-material processing approach is the result of years of experience working on printed electronics, refining the knowledge of various additive manufacturing avenues, and a deep understanding of photonic processing done over a wide variety of materials. These results will undoubtedly be useful in the future development of flexible, high-performance optoelectronic devices and contribute with the advancement of scientific knowledge for materials processing in printed electronics. The results of additional research projects are also presented as part of this thesis. First, the work done with chalcogenide lead-sulfide nanocrystals, that included mastering the synthesis of PbS quantum dots for size control and characterization of their optical properties. These were utilized in QD assemblies using ligand exchange to build photodetectors and a quantum dot sensitized solar cell made with TiO2. The fill-factor of this device was improved by the addition of multi-walled carbon nanotubes that facilitated the charge extraction. Second, an industrial project that aimed to understand and optimize the fabrication of graphene-based inks for screen printing, made with an industrial-grade graphene. This project demanded understanding the properties of graphene materials by doing in-depth analysis of its Raman characteristics, and how the material responds to different post-processing techniques to create screen-printing inks.

Date	24 Apr 2024
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Sylvain G. Cloutier (Supervisor)