Figure 1

Understanding the effect of Ga addition on thermoelectric performance of pristine and Ga-doped Cu₂Te. Synergistic effects of Ga doping in Cu₂Te within certain limits (moderate doping ~3%) resulting in a large conductivity (σ), optimized thermopower (S), moderate thermal conductivity (κ) performance, thereby extensively enhancing the ZT of Cu₂Te at medium temperatures. With the increase of Ga doping content, there was an enlarged carrier conductivity (σ), due to the injection of immense p-type carriers assuming the shape of a “hump” in the valence band minimum (VBM). Subsequently, the minority charge carriers (e−) got coupled with the dopant Ga³⁺ ions forming localized cloud of charge carriers. On the application of a temperature gradient, this charge localization enhanced the thermopower (S) of the device significantly. However, Ga doping also exerted an adverse effect if it is not restricted within certain limits owing to the increased number of thermally active phonon modes in disordered species (CuGaTe₂) resulting in higher κ (enhanced doping ~5%). Since ZT = \(\frac{{S}^{2}\sigma T}{\kappa }\), there exists a trade-off between enlarged electrical transport (σ, S) & heat transport (κ) coefficients as a consequence of Ga doping. Optimization of the TE efficiency ZT was achieved at moderate Ga doping levels (~3%), as shown by arrow, owing to a substantial σ, large S and moderate κ.