Crystal structure and mechanical properties of spark plasma sintered Cu2Se: An efficient photovoltaic and thermoelectric material

• Crystal structure determination by stereographic projections for Cu2Se.
• Superior mechanical properties coupled with high thermoelectric performance.
• Improved fracture toughness, compressive strength and thermal shock resistance.

Copper selenide (Cu2Se) based materials are currently being investigated globally for efficient photovoltaic and thermoelectric (TE) device applications. Despite having enormous device potential its crystal structure and mechanical properties are still not fully explored owing to its complex behavior. Stereographic projection is one of such useful tools to estimate the crystallography of the material conclusively. In the current study, the crystal structure of α and β-phases of Cu2Se was determined by its stereographic projections in reciprocal space. Further, mechanical properties of Cu2Se are highly important to avoid catastrophic failure and ensure longevity of the TE devices made out of these materials. Cu2Se exhibited the compressive strength of ~45 MPa with ~3% of plastic strain and a fracture toughness value of ~2±0.02 MPa√m, the latter being significantly higher than that of the other known TE materials. Finally, thermal shock resistance, which is one of the crucial parameters for the stability and longevity of the device applications, was calculated to be ~281±12 W m−1. Superior mechanical properties coupled with highly reported thermoelectric behavior makes Cu2Se as a potential candidate for green energy generation.