The solar cell industry requires convenient and inexpensive fabrication of semiconductor nanostructures as highly efficient absorptive layers with low-cost, environmentally benign, heavy-metal-free (i.e., free from Hg, Cd, and Pb) and suitable band gap near 1 eV features. In this paper, we demonstrate the synthesis of two-dimensional single-crystal berzelianite (Cu_2−xSe) nanosheets (in-plane diameter-to-thickness ratio ∼100) and nanoplates (in-plane diameter-to-thickness ratio ∼10) via a simple, “green” and environmentally benign method of injecting Cu(I)-complex precursor into Se-solution in paraffin liquid. Unlike the previous syntheses of binary chalcogenide nanostructures such as CdSe, the current strategy for berzelianite synthesis does not use expensive and toxic phosphine ligands such as trioctylphosphine (TOP). The products were characterized by a range of methods, such as X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected area electron diffraction, revealing that the products have the cubic phase and high-quality single-crystal two-dimensional nanostructure. UV-Vis-NIR absorption spectroscopy reveals that the nanosheets and nanoplates show obvious absorption onsets at 0.89 eV and 0.80 eV, respectively, and strong optical absorption peak at 1.70 eV and 1.62 eV, covering the whole red range of the solar spectrum. The present study opens a new avenue to “green” and low-cost controllable synthesis of binary chalcogenides with technological applications in solar energy conversion and also in a wide range of photonic devices operating in the near-infrared.