Low-Voltage, Low-Waste Fabrication of Semiconducting Thin Films by Continuous Flow Electrophoretic Deposition

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One of the most significant impediments to the widespread use of solar energy is the manufacturing cost of the solar cell modules. Electrophoretic deposition, which uses an electric field to drive charged particles to a surface and which is scalable and low cost, presents a compelling solution to this manufacturing problem. This project will study electrophoretic deposition of inorganic semiconducting materials. The objective of this project is to electrophoretically deposit thin films from an ink comprised of nanometer-scale semiconductor crystals dispersed in a solvent. This research could lead to inexpensive, efficient, and sustainable processing methods for manufacturing solar cells from earth-abundant, non-toxic materials. The project will provide graduate and undergraduate students multidisciplinary training in cutting edge nanomanufacturing processes. The research results and accomplishments will be shared at public events, integrated into lectures and lab-based undergraduate courses and brought into the classrooms of a local public school. The objective of this project is to use colloidal, all-inorganic, nanocrystal dispersions in polar, non-aqueous electrolytes for low-voltage electrophoretic deposition. The hypothesis will be tested that the threshold voltage for electrophoretic deposition can be lowered by an order of magnitude to less than 1 volt under conditions in which electrolysis of the electrolyte is coupled with deposition of the electrophoresing particles. Such low voltages would lead to low deposition rates in conventional reactors. Therefore, a second hypothesis will be tested that continuously flowing the nanocrystal dispersion through an electrophoretic deposition microreactor can achieve both high deposition rate and thick films. Flow rate, reactor geometry, and applied bias can be tuned to achieve near-complete utilization of the nanocrystal feedstock and minimal waste generation. Work will focus on earth-abundant, non-toxic nanocrystals of copper zinc tin sulfide and lead sulfide, which have been used in the highest efficiency quantum dot solar cells. This research will deepen understanding of directed- and self-assembly processes under the influence of applied electric fields, focusing on the poorly understood, non-equilibrium behavior of chemically reactive ions at the intersection of bulk and nanoscale charged surfaces. Specifically it will probe the fundamental mechanism of electrophoretic deposition at low voltage.