Revealing the Mechanisms of Bulk Material Dissolution in Thiol-Amine Solvent Mixtures Toward the Solution Deposition of Chalcogenide Thin Films

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NON-TECHNICAL SUMMARY: The macroelectronics industry has emerged as a powerful entity with widespread deployment of thin film technologies, such as solar cells and flat panel displays. These macroelectronics applications require innovative approaches to low-cost, large-area electronics, as the drivers are not compatible with the larger and more well-established microelectronics industry. To reduce costs and improve market potential for thin film macroelectronics, research into next-generation macroelectronic thin film deposition and processing must include a focus on low-temperature solution processing. The principal investigator is studying a solvent mixture used to dissolve cheap bulk materials to make inks that, upon solution deposition, convert to semiconductor thin films under mild conditions. The primary goals of this project include understanding the chemistry of bulk material dissolution and leveraging that information to deposit stable semiconductor thin films of novel composition that are promising for next-generation solar cells. Integrated into this plan is an outreach program specifically aimed at local community college students. The principal investigator is partnering with Cerritos Community College, an institution with a large number of underrepresented students, to provide internships on materials research. The objective of this annual 8-week outreach program is to provide these students with STEM research opportunities that are not afforded to them at the community college level, and thereby increase their transfer rate to 4-year institutions. An internship alumni network will be established to maintain formal contact with the interns after they complete the program.TECHNICAL SUMMARY: Despite decades of developments in semiconductor thin film deposition, the vast majority of methods require costly, energy intensive conditions. As such, there is a need to develop deposition processes that are less capital- and energy-intensive. The direct dissolution of bulk materials to yield solution processable inks that convert to thin films under mild conditions can result in significant cost reductions. This project directly addresses the challenge by studying inks prepared by bulk chalcogenide, oxide, and metal dissolution with thiol-amine solvent mixtures. The principal investigator is leveraging his expertise in inorganic chemistry and materials synthesis to meet the following objectives: (1) Understand the chemistry behind the dissolution of bulk materials with the thiol-amine solvent mixture. While a wide scope of bulk materials has demonstrated solubility in this solvent mixture, there is little to no understanding of the dissolution mechanism. The dissolution mechanism is being interrogated through an examination of the resulting molecular solutes and the chemical factors that affect the kinetics of dissolution. In parallel, a dual-space approach that combines Rietveld refinement and pair distribution function (PDF) analysis of X-ray total scattering data is being employed to monitor thermal conversion of the amorphous dried molecular inks into crystalline chalcogenide thin films. This approach is intelligently informing solution processing and crystallization of phase-pure, high-quality chalcogenide thin films. (2) Use the thiol-amine solvent mixture to solution process promising chalcogenide thin films for solar energy conversion. The large palette of inks now available with this system are being used to solution process more novel, compositionally complex, multinary chalcogenide semiconductor thin films with properties amenable to solar energy conversion, such as optimal band gap, polar crystal structures, and materials with high thermodynamic stability comprised of Earth abundant elements. The most promising candidates are being explored in next-generation solar cells.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.