Utilizing Diselenide Precursors toward Rationally Controlled Synthesis of Metastable CuInSe2 Nanocrystals

Within the past decade, there has been an emergence of reports regarding the synthetic isolation of multinary metal chalcogenide nanocrystals that persist under ambient conditions with metastable crystal structures; however, many of the direct syntheses remain largely serendipitous with respect to the conditions needed to achieve the metastable product. Toward the development of more rational design principles that enable the predictable isolation of metastable nanocrystals, we demonstrate a molecular programming approach for the synthesis of CuInSe2 nanocrystals utilizing diorganyl diselenide precursors of the structure R-Se-Se-R Specifically, we show that the kinetics of diselenide precursor conversion are dependent upon C-Se and Se Se bond dissociation energies and that the strength of the C-Se bond is the phase-directing variable. When dibenzyl and dimethyl diselenide precursors with relatively weaker C-Se bonds are employed, the resulting nanocrystals form in the thermodynamically stable chalcopyrite phase of CuInSe2. However, precursors like diphenyl diselenide that possess stronger C-Se bonds alter the reaction kinetics so as to steer the reaction toward formation of the metastable wurtzite-like phase. These two phases form via distinct copper selenide intermediates, with chalcopyrite forming through Cu2-xSe and the wurtzite-like phase forming through Cu3Se2 intermediates, and it was found that the ultimate wurtzite-like phase displays remarkable resistance to relaxation to the chalcopyrite phase. This molecular programming approach should be applicable toward the isolation of other metastable phases of metal chalcogenide nanocrystals.