Raising the Thermoelectric Performance of p-Type PbS with Endotaxial Nanostructuring and Valence-Band Offset Engineering Using CdS and ZnS
Raising the Thermoelectric Performance of p-Type PbS with Endotaxial Nanostructuring and Valence-Band Offset Engineering Using CdS and ZnS
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DOI：
10.1021/ja306527n
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发表时间：
2012-10-03
影响因子：
15
通讯作者：
Kanatzidis, Mercouri G.
中科院分区：
文献类型：
--
作者：
Zhao, Li-Dong;He, Jiaqing;Kanatzidis, Mercouri G.
我们详细研究了CdS和ZnS作为第二相对p型PbS热电性能的影响。我们报告了在923 K时，对于2.5 at.% Na掺杂的p型PbS，具有3.0at.%的纳米结构CdS。我们将高ZT归因于在多个长度尺度上的宽基声子散射的组合，以降低（晶格）热导率和通过PbS基质和金属硫化物纳米相沉淀物之间的相干界面的有利电荷传输，这保持了必要的高载流子电导率和相关的功率因数。类似于大离子键合的金属硫化物（ZnS、CaS和SrS），共价键合的CdS也可以有效地降低p型PbS中的晶格热导率。通过透射电子显微镜证实了无处不在的纳米结构的存在。价和导带能级的NaCl型金属硫化物，MS（M = Pb，Cd，Zn，Ca和Sr）从密度泛函理论计算，以深入了解PbS和这些材料中的第二相之间的能带排列。空穴传输是通过主机PbS和嵌入的第二相MS（M = Cd，Zn，Ca和Sr）之间的价带对齐的能带偏移最小化控制的。最小的价带偏移约0.13 eV，在OK之间的PbS和CdS，这是进一步减少在升高的温度下的热带展宽。这允许载体在轴向排列的成分（即，基质和纳米结构），从而使空穴迁移率和功率因数的显著恶化最小化。我们得出了PbS系统的热电性能的结论，并且推而广之，其他系统可以通过嵌入内轴纳米结构第二相的紧密耦合的声子阻挡/电子传输方法来增强。
We have investigated in detail the effect of CdS and ZnS as second phases on the thermoelectric properties of p-type PbS. We report a ZT of similar to 1.3 at 923 K for 2.5 at.% Na-doped p-type PbS with endota)dally nanostructured 3.0 at.% CdS. We attribute the high ZT to the combination of broad-based phonon scattering on multiple length scales to reduce (lattice) thermal conductivity and favorable charge transport through coherent interfaces between the PbS matrix and metal sulfide nanophase precipitates, which maintains the requisite high carrier conductivity and the associated power factor. Similar to large ionically bonded metal sulfides (ZnS, CaS, and SrS), the covalently bonded CdS can also effectively reduce the lattice thermal conductivity in p-type PbS. The presence of ubiquitous nanostructuring was confirmed by transmission electron microscopy. Valence and conduction band energy levels of the NaCl-type metal sulfides, MS (M = Pb, Cd, Zn, Ca, and Sr) were calculated from density functional theory to gain insight into the band alignment between PbS and the second phases in these materials. The hole transport is controlled by band offset minimization through the alignment of valence bands between the host PbS and the embedded second phases, MS (M = Cd, Zn, Ca, and Sr). The smallest valence band offset of about 0.13 eV at OK was found between PbS and CdS which is diminished further by thermal band broadening at elevated temperature. This allows carrier transport between the endotaxially aligned components (i.e., matrix and nanostructure), thus minimizing significant deterioration of the hole mobility and power factor. We conclude the thermoelectric performance of the PbS system and, by extension, other systems can be enhanced by means of a closely coupled phonon-blocking/electron-transmitting approach through embedding endotaxially nanostructured second phases.