2D Copper Thiolate Coordination Polymer as a Molecular Precursor for the Selective Synthesis of Photoresponsive Digenite (Cu_1.8S) and Covellite (CuS) Phases

Copper sulfide nanostructures have attracted significant attention in green energy technologies owing to their earth-abundant nature and promising optoelectronic properties. In this study, we report a reproducible, phase-selective synthesis of nanocrystalline copper sulfides, namely, diginite (Cu1.8S) and covellite (CuS), via low-temperature thermolysis of a newly synthesized two-dimensional (2D) copper thiolate coordination polymer: [(PEt3)2Cu2(4-Spy)2]n (2D-CuSpy) as a single-source molecular precursor. The precursor undergoes facile thermal decomposition to yield copper sulfide nanoparticles under mild conditions. Comprehensive characterization using powder X-ray diffraction (pXRD), electron microscopy, and diffuse reflectance spectroscopy confirms the phase purity, morphology, and tunable bandgap (1.8–2.1 eV) of the resulting nanostructures. Notably, the solvent choice was found to significantly influence the phase and morphology of the final products. Prototype photoelectrochemical cells fabricated with the pristine nanomaterials demonstrated excellent photocurrent response and rapid photoswitching behavior, highlighting their potential as alternative photon-absorbing materials for sustainable energy conversion.