Phase Selective Synthesis Of Cu₂Se And Mechanism Study Of The α-Cu₂Se/β-Cu₂Se Phase Transition

Cu2Se compounds is an intrinsic p-type semiconductor which has a direct band gap of 2.2 eV and an indirect band gap of 1.4 eV. Since the indirect band gap is very close to the optimal value of photovoltaic absorbing layer material, Cu2 Se is considered the suitable photovoltaic material. In addition, Cu atoms in the structure of ?-Cu2 Se has a liquid-like mobility, making Cu2 Se having high conductivity and low thermal conductivity at the same time. Since its structure is in line with the "electronic crystal- phonon glass" concept of thermoelectric materials, Cu2 Se gets sustained attention in recent years.Cu2Se materials exists in various crystallographic systems, including tetragona, orthogonal, orthorhombic and cubic crystal. But only the application of cubic Cu2 Se was widely discussed, partly due to that the cubic Cu2 Se is the stable phase at room temperature. The metastable phase Cu2 Se are seldom reported and the related research is still in very primary stage. This thesis provides a method to synthesize metastable Cu2 Se. The phase selective synthesis mechanism is different from that reported in literatures. The research content of this paper are as follows:(1) This paper provides a solvothermal synthesis method in which the phase of Cu2 Se materials can be selected. By adding suitable amount of antimonide at the beginning of the reaction, metastable ?-Cu2 Se can be produced through 14-hour solvothermal reaction at 200 ?C.(2) The solvothermal synthesis method provides a simple phase selective synthesis methods for Cu2 Se just by introducing antimony source. By examing the product of every reaction stage using ex-situ XRD analysis, the phase selection synthesis reaction path was further discussed, confirming that there is a underlying ?-Cu2 Se to ?-Cu2 Se transformation in this reaction route.(3) On the basis of kinetics study of different reaction stages, we proposed a mechanism of transition from thermodynamical stable phase to metastable phase induced by SbCl3 additive. Further investigations indicate that effective constituent Sb can only react with β-Cu2 Se and triggered a transition from β to ? at a special occasion associated with the temperature and constituent dependent β-Cu2 Se lattice structure.