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    Optimizing Solid-State Ligand Exchange for Colloidal Quantum Dot Optoelectronics: How Much Is Enough?

    Year: 2020

    Journal: ACS Appl. Energ. Mater., Volume 3, JUN 22, page 5385–5392

    Authors: Kirmani, Ahmad R.; Walters, Grant W.; Kim, Taesoo; Sargent, Edward H.; Amassian, Aram

    Keywords: colloidal quantum dots; solar cells; solid-state ligand exchange; 3-mercaptopropionic acid; 1,2-ethanedithiol

    Progress in chalcogenide and perovskite CQD optoelectronics has relied to a significant extent on solid-state ligand exchanges (SSEs): the replacement of initial insulating ligands with shorter conducting linkers on CQD surfaces. Herein we develop a mechanistic model of SSE employing 3-mercaptopropionic acid (MPA) and 1,2-ethanedithiol (EDT) as the linkers. The model suggests that optimal linker concentrations lead to efficient exchange, resulting in ca. 200-300 exchanged ligands per CQD, a 50% thickness reduction of the initial film, decreased interdot spacing, a 15 nm red-shift in the excitonic absorption peak, and a 10x reduction in carrier lifetime. It is the combined effect of these physicochemical changes that has traditionally made 1% MPA and 10(-2)% EDT (v:v) the concentrations of choice for efficient CQD optoelectronics.
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