This thesis reports the design, fabrication, and operation of silicone based multiplexed electrospray (MES) emitters. After reviewing the feasibility of utilizing electrospray as a scalable thin film deposition technique as well as the advantages and limitations of prior MES emitters, we present a design rationale for MES suitable for highly conductive and corrosive fluids. Then we customized a 1064nm fiber laser micromachining system to precisely and rapidly machine silicone sheet and silicon wafers. Laser energy and path are judicially chosen to create clean and round micro posts that form the external structure of the nozzles. For MES with low flow rate per nozzle, it is of vital importance to evenly distribute the liquid into each nozzle on the entire MES array by controlling the pressure drop inside each fluid flow channel. To this end, we modeled the dimension of microfluidic channels that introduce flow impedance overwhelming surface tension at the nozzle tip. We presented laser microfabrication techniques for fabricating two typical types of microfluidic channels: the through-hole array on conductive silicone sheets and the in-plane microfluidic channel on silicon wafers. Next, we developed a convenient assemble process for the integration of three layers (distributor layer, extractor layer, and collector layer) of the MES emitter. The uniformity of the flow rate among nozzles on MES emitters was investigated by observing the overall spray profiles and measuring the diameter of each jet. The results suggest that the silicone-based MES emitters are feasible for spraying highly conductive and corrosive liquids. The MES emitter developed in this thesis may become a promising tool in the scalable manufacturing of thin film perovskite solar cells. / Master of Science / Liquid sprays have widespread applications such as spray coating, spray drying, spray pyrolysis, and spray cooling. Among various types of sprays, electrohydrodynamic spray (electrospray) has several unique properties such as quasi-monodispersity, tunable droplet size from a few micrometer to nanometers, and compatible with roll-to-roll processing of advanced materials. On the other hand, solution-processed perovskite solar cells have attracted immense research interest recently: within the past seven years, efficiencies of perovskite solar cells have rapidly increased from 3.8% to over 20%. Electrospray is a potential film deposition technique to replace spin coating for continuously fabricating thin-film perovskite solar cells with large areas and virtually no material waste. However, two major challenges exist for electrospraying liquid solutions of perovskite precursors. First, the solution is highly corrosive due to lead (Pb) ions which prevent the use of common metals (i.e. copper, stainless steel, and aluminum). Second, the solution is highly electrical conductive which demands low flow rates (~100nL/min) which make it difficult to multiplex. This thesis reports the design, fabrication, and operation of silicone based multiplexed electrospray (MES) emitters. After reviewing the feasibility of utilizing electrospray as a scalable thin film deposition technique as well as the advantages and limitations of prior MES emitters, we present a design rationale for MES suitable for highly conductive and corrosive fluids. Then we customized a 1064nm fiber laser micromachining system to precisely and rapidly machine silicone sheet and silicon wafers. Laser energy and path are judicially chosen to create clean and round micro posts that form the external structure of the nozzles. For MES with low flow rate per nozzle, it is of vital importance to evenly distribute the liquid into each nozzle on the entire MES array by controlling the pressure drop inside each fluid flow channel. To this end, we modeled the dimension of microfluidic channels that introduce flow impedance overwhelming surface tension at the nozzle tip. We presented v laser microfabrication techniques for fabricating two typical types of microfluidic channels: the through-hole array on conductive silicone sheets and the in-plane microfluidic channel on silicon wafers. Next, we developed a convenient assemble process for the integration of three layers (distributor layer, extractor layer, and collector layer) of the MES emitter. The uniformity of the flow rate among nozzles on MES emitters was investigated by observing the overall spray profiles and measuring the diameter of each jet. The results suggest that the silicone-based MES emitters are feasible for spraying highly conductive and corrosive liquids. The MES emitter developed in this thesis may become a promising tool in scalable manufacturing of thin film perovskite solar cells.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/78199 |
| Date | 14 June 2017 |
| Creators | Li, Liurui |
| Contributors | Mechanical Engineering, Deng, Weiwei, Liu, Yang, Cheng, Jiangtao |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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