Facile one pot synthesis of highly photoresponsive coinage metal selenides (Cu1.8Se and Ag2Se) achieved through novel Cu and Ag pyridylselenolates as molecular precursors

Copper selenide (Cu1.8Se) and silver selenide (Ag2Se) have garnered unprecedented attention as efficient absorber materials for cost-effective and sustainable solar cells. Phase pure preparation of these exotic materials in a nano-regime is highly desirable. This account outlines a simple and easily scalable pathway to Cu1.8Se and Ag2Se nanocrystals using novel complexes [Cu{2-SeC5H2(Me-4,6)2N}]4 (1), [Ag{2-SeC5H2(Me-4,6)2N}]6 (2) and [Ag{2-SeC5H3(Me-5)N}]6·2C6H5CH3 (3·2C6H5CH3) as single source molecular precursors (SSPs). Structural studies revealed that the Cu and Ag complexes crystallize into tetrameric and hexameric forms, respectively. This observed structural diversity in the complexes has been rationalized via DFT calculations and attributed to metal-metal bond endorsed energetics. The thermolysis at relatively lower temperature in oleylamine of complex 1 afforded cubic berzelianite Cu1.8Se and complexes 2 and 3 produced orthorhombic naumannite Ag2Se nanocrystals. The low temperature synthesis of these nanocrystals seems to be driven by the observed preformed Cu4Se4 and Ag6Se6 core in the complexes which have close resemblance with the bulk structure of the final materials (Cu1.8Se and Ag2Se). The crystal structure, phase purity, morphology, elemental composition and band gap of these nanocrystals were determined from pXRD, electron microscopy (SEM and TEM), EDS and DRS-UV, respectively. The band gap of these nanocrystals lies in the range suitable for solar cell applications. Finally, these nanocrystal-based prototype photo-electrochemical cells exhibit high photoresponsivity and stability under alternating light and dark conditions.