Structure And Thermoelectric Properties Of CuIn₃Se₅ Based Ternary Semiconductors

Thermoelectic material is a type of new functional materials which can convert heat to electricity directly with the help of the internal carrier motion within solids.CuIn₃Se5-based semiconductor is one of a non-cubic diamond-like compounds with chalcopyrite structure（space group:1-42d）.Owing to its inherent Coulomb attraction between the charged InCu²⁺ and 2 Vcu-defect pairs which has a profound effect on the electronic and structural properties,the chalcopyrite has attracted much attention in thermoelectrics.In this work,we have synthesized the Te-substituted for Se CuIn₃Se5-xTex（x=0,0.05,0.1,0.2,0.5）alloys by using powder metallurgy method along with spark plasmas intering（SPS）technique.Since the electronegativity of element Te（2.1 eV）,which is a little higher than those of In（1.78 eV）and Cu（1.90 eV）,is smaller than that of Se（2.55 eV）,therefore,the substitution of Te for Se tends to elongate the bond lengths dCu-Se and dIn-Se,leading to the change of crystal structure parameters of u and η,which is directly related to lattice thermal conductivity（KL）.In this work,we have observed that at x=0.1 the anion position displacement △u（u-0.25）equals to 0.15×10-3,at which the band gap and carrier concentration reach the highest and the crystal structure suffers distortion to a certain degree.At the same time,the material gives the minimum lattice thernal conductivity（kL）,due to the strongest phonon scattering.We therefore conclude that the best thermoelectric performance can be achieved at a certain △u value,rather than at Au=0.The sample CuIn₃Se5-xTex（x=0.1）gives the highest ZT value（0.4）at 930 K,which is about 2.6 times that of pristine CuIn₃Se5（ZT=0.015 at 930 K）.Based on the optimized CuIn₃Se4.9Te0.1,we have also prepared Ag substituted Cu1-xAgxIn₃Se4 9Te0.1（x=0.05,0.1,0.2,0.3）alloys for Cu.The measurement shows that the highest ZT value of 0.46 at 930 K was attained for the Cu1-xAgxIn₃Se4.9Te0.1（x=0.2）alloy,which is about 3.1 times that of CuIn₃Se5（930K,ZT=0.15）.Na and Cl elements have substituted in Cu1-xNaxIn₃Se5-xClx（x=0,0.05,0.1,0.2）alloys for Cu and Se simultaneously.The measurement shows that the highest ZT value of 0.38 at 930 K was attained for the Cu1-xNaxIn₃Se5-xClx（x=0.1）alloy,which is about 2.54 times that of CuIn₃Se5（930 K,ZT=0.15）.