Investigations of the Copper Bromide–Ethylenediamine System: The Hydrothermal Synthesis and X-Ray Crystal Structure of [Cu(H2NCH2CH2NH2)2] [{Cu2Br4}] and [Cu(H2NCH2CH2NH2)2] [{Cu5Br7}]

A chemical deposition method for fabrication of Cu3Se2 and CuSe thin films is presented. The filmsʹ growth is based on the decomposition of selenosulfate in alkaline solution containing a copper(II) salt and a suitable complexing agent. The deposited materials were identified by X-ray diffraction. In addition, optical investigations were performed. The absorption onset in the optical spectra of the annealed Cu3Se2 films showed a slight red shift (compared to the as-deposited ones), indicating a very slight increase in the average crystal size. The optical (direct) band gap energy of Cu3Se2 thin films is 2.37 eV, while the CuSe thin films are characterized with two direct band gap energies of 2.0 and 2.8 eV. The average crystal size values, calculated on the basis of the recorded XRD patterns, are approximately 40 nm for both Cu3Se2 and CuSe thin films.