Nearly dispersed marcasite CuSe2 (m-CuSe2) and berzelianite Cu2Se (b-CuSe2) crystals were successfully synthesized using copper and selenium-triethylene glycol (TEG) solution thermal decomposition using triethylenetetramine (TETA) as the reducing agent and polyvinylpyrrolidone (PVP) as the capping agent. The crystalline structure, electronic and copper selenide particles optical characterization were investigated using X-ray diffractometer (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorbance spectra. The TETA addition effects on crystal phase development and morphology were investigated. The obtained copper selenides are m-CuSe2 and b-CuSe2 for the samples added with TETA of 0.007 M and 0.147 M, respectively. The measured energy gaps for m-CuSe2 and b-CuSe2 are 1.49 eV and 1.98 eV, respectively. The marcasite CuSe2 can be obtained by annealing krutaite CuSe2 at a higher temperature.