Bandgap reduction responsible for the improved thermoelectric performance of bulk polycrystalline In2–xCuxSe3 (x = 0−0.2)

Abstract

α-In2Se3 is of large bandgap (∼1.4 eV) semiconductor and its structure is based on two-layer hexagonally packed arrays of selenium atoms with 1/3 of the sites of indium atoms being empty. Here we report a bandgap Eg reduction due mainly to the formation of a Cu2Se slab in the host In2Se3, which is responsible for the remarkable improvement of thermoelectric performance of bulk polycrystalline In2−xCuxSe3 (x = 0.1–0.2). When x = 0.2 the dimensionless figure of merit ZT and power factor were increased by a factor of 2 and 3, respectively, at 846 K if compared to those of Cu-free In2Se3. Interestingly, an incorporation of Cu into the lattice of In2Se3 results in a change in morphology from amorphouslike structure represented by In2Se3 to a visible polycrystalline form attributed to partial crystallization of the structure. This change enhances lattice thermal conductivities κL over the very low values of In2Se3. However, the enhancement is only moderate because of the effective scattering of phonons in the polycrystalline nanostructure.

Indium Selenides: Structural Characteristics, Synthesis and Their Thermoelectric Performances

“…Several investigations were performed in order to measure and improve the electrical and thermal properties of In 2 Se 3 and InSe. [51b], – Cui et al . investigated the thermoelectric properties of n‐type α(2H)‐In 2 Se 3 and Ag/Cu‐incorporated In 2 Se 3 fabricated through melting.…”

Thermoelectric properties of Cu2Ga4Te7 based compounds with Zn substitution for Cu and Ga

“…Of course, we can not ignore another fact proposed by Honeyman and Wilkinson , who found that energy gap increases with the crystalline ionicity and believed that the widening of E g could also result from an increase in ionicity upon the substitutions of Zn. The widening of E g is directly responsible for the degradation in σ in the present material systems , which is why we observed degradation in electrical conductivities in both series of materials when Zn content increases.…”

“…In addition, the creation of the decreases the d character of the valence band, causing the reduction of d–p hybridization and leading to the widening of the bandgap ( E g ) . It has been confirmed that the widening of E g can decrease the electrical conductivity .…”

Manipulation of the crystal structure defects: An alternative route to the reduction in lattice thermal conductivity and improvement in thermoelectric performance of CuGaTe2

“…20 All the CGT samples were annealed in silica vacuum tubes at 663 K with the holding time varying from 240 h to 1440 h (the four samples are each denominated as S-24, S-36, S-72, and S-144. Here, the numbers 24, 36, 72, and 144 refer to the annealing time 240 h, 360 h, 720 h, and 1440 h).…”