Sturctures And Thermoelectric Properties Of Doped-In₂Se₃-based Semiconductors

In2Se3 is one of the typical A2IIIB3 VI type wide bandgap semiconductor compound. There exist several phases under appropriate temperatures, whose intrinsic characteristic structures govern their corresponding main physical properties. In this work, we have modified the structure and thermoelectric(TE)performance upon impurity doping in In2Se3, and attained the results which are summarized below:1、In α-In2Se3 there are many lattice defects such as 1/3 In vacancies(VIn),non-stoichiometric Se vacancies(VSe) and interstitial Ini. In this work, we substitute isoelectronically element S for Se to fabricate one group of materials In2 Sx Se3-x(x=0,0.05,0.2,0.5), and found that with the S incorporation in α-In2Se3 the rearrangement of lattice disorders occurs, which avoids the annihilation of VIn and interstitial Ini acting as donor, and thereby increases the free carrier concentration and improves the electrical conductivity. Besides, the lattice distortion created by newly-formed defects SSe upon S incorporation into the Se sites enhances the phonon scattering, which reduces the lattice thermal conductivities κL. As a consequence, we have improved the thermoelectric properties of the material, and achieved a ZT value of 0.67 in α-In2S0.05Se2.95 in perpendicular to the pressing direction at 923 K, which is about 2.8 times that ofvirgin α-In2Se3.2、γ?In2Se3 has a defected wurtzite structure which can be stabilized at room temperature, in which 1/3 In vacancies(VIn) are ordered in screw form along the c axis. In our work, We have prepared Li+-added γ?In2Se3 compounds by means of ion diffusion in aqueous solution. Through controlling the time and temperature of the ion diffusion in the aqueous solution respectively,we have investigated the effect of the time and temperature on the structure and thermoelectric performance. The results shows that that the Li+has a potential to occupy the In vacancies(VIn), which increases the free carrier concentration and improves the electrical conductivity, and at the same time, the Li+incorporation cause the lattice distortion to some extent, which thereby enhance the phonon scattering and reduces the lattice part κL. Besides, we have determined the optimal diffusion time and temperature which are 30 h and 50℃ respectively,therefore, a good TE performance is achieved with the ZT value of 0.63 at 923 K under current conditions, which is about 3.1 times that of virgin γ?In2Se3.