Realizing high thermoelectric properties in p-type polycrystalline SnSe by inducing DOS distortion

SnSe crystals have been discovered as one of the most efficient thermoelectric materials due to their remarkable thermal and electrical transports. But the polycrystalline SnSe possesses much lower performance especially for the low carrier mobility and electrical conductivity. We firstly attempted to explain and verify the difference in the electrical conductivity as a function of temperature between p-type crystalline and polycrystalline SnSe by considering the grain boundary effects in the polycrystalline samples. On the basis of 2% Na doping to optimize the carrier concentration, the carrier mobility is improved by further introducing In, leading to enhanced carrier mobility from 3 to 9 cm 2 ·V −1 ·s −1 in polycrystalline SnSe. Moreover, In doping introduces extra resonant levels in SnSe, which increases the density of states near Fermi level and leads to an enhanced band effective mass. Large Seebeck coefficient of ~ 205 μV·K −1 at 300 K and maximum power factor of ~ 7.5 μW·cm −1 ·K −2 at 773 K can be obtained in the Sn 0.975 Na 0.02 In 0.005 Se sample, leading to a competitively high dimensionless figure of merit ( ZT ) value exceeding 1.1 at 773 K. 摘要 晶体 SnSe 由于出色的电声传输性能, 不断表现出优异的热电特性。但是, 相对于晶体, 多晶 SnSe 的电导率和载流子迁移率呈现数量级的降低。首先, 我们试图通过考虑多晶样品中晶界的影响来解释 p 型晶体 SnSe 和多晶 SnSe 的电导率随温度变化的差异。通过掺杂 2% 的 Na 来优化多晶 SnSe 的载流子浓度, 在此基础上引入 In 提高了基体的载流子迁移率, 样品的室温迁移率由 3 cm 2 ·V -1 ·s -1 增加到 9 cm 2 ·V -1 ·s -1 。此外, 通过在多晶 SnSe 中掺杂 In 引入了额外的共振能级, 增加了费米能级附近的态密度, 提高了能带有效质量 。引入 In 之后, Sn 0.975 Na 0.02 In 0.005 Se样品在 300 K 时的塞贝克系数从 ~ 137提高到 ~ 205 μ V·K -1 , 在 773 K 时的最大功率因子从 ~ 3.9提 高到 ~ 7.5 μ W·cm -1 ·K -2 , 使热电优值 ( ZT ) 在 773 K 时超过了 1.1 Graphical Abstract