Thermoelectric Property of n-Type Bismuth-Doped SnSe Film: Influence of Characteristic Film Defect

Abstract

Highly aligned SnSe exhibits very high thermoelectric properties, and orientation control in films is very promising for developing high-performance thermoelectric modules. While SnSe films with intrinsic p-type nature have been reported, fabrication of the highly aligned n-type SnSe films is difficult due to thermodynamic restriction on the solubility of the doping elements. Here, highly oriented SnSe films doped with Bi were successfully fabricated using pulsed laser deposition. Characteristic film structures were observed: doped Bi in the SnSe matrix; domain boundaries with a spacing of ∼200 nm; self-organized Bi precipitates with a bimodal size distribution; and stacking faults. The most important result is observation of the n-type Hall resistivity and the n-type Seebeck coefficient. The stacking faults and the doped Bi in the films degraded the room-temperature Seebeck coefficient. While the electron carrier mobility in room temperature was smaller than that in the single crystal due to the domain boundary scattering, the domain boundary scattering was suppressed in the high temperature of 300 °C. Thus, the characteristic film structures significantly affect the thermoelectric properties of SnSe. The doped Bi in the SnSe matrix, the stacking faults, and the domain boundaries should be controlled for further improvement of the thermoelectric properties in the Bi-SnSe films, and the self-organized Bi nanoprecipitates are very promising for achieving high-performance Bi-SnSe with decreased thermal conductivity.

The ultra-high thermoelectric power factor in facile and scalable single-step thermal evaporation fabricated composite SnSe/Bi thin films

“…76,81,82 In our case due to the presence of multiphase materials, energy filtering, improved grain sizes, and enhanced mobility would lead to an increase in s and S simultaneously at the desired temperature. Similar trends of the variation of S and s were also reported for SnSe previously [82][83][84] in the measured temperature range, in doped 46 and composite form. 77,79,85 Also, SnSe with the vacancy of Se atoms shows such a type of behavior.…”

“…These improved thermoelectric performances by effectively increasing the carrier density up to 2 orders. 28,46,48,52,[73][74][75] Room temperature Hall measurement gives the carrier concentrations of 1.8 Â 10 18 , 1.87 Â 10 19 , and 9.1 Â 10 19 , respectively, for S1, S2, and S3. It is clear from Hall measurement that B2 orders of magnitude is increased from S1 to S3, upon adding Bi.…”

“…The metallic phase has a symmetric density of states and its bipolar nature has resulted in the overall very low Seebeck coefficient (due to the difference in carrier mobility). 46,76,77 However, for the multiphase material, bipolar conduction can be effectively suppressed by interface boundaries of different phases. These boundaries act as a potential barrier to a particular type of carrier and give easy crossing access to other types of carriers.…”

“…They employed SnSe ink with a binder and achieved a high value of ZT (1.7) at 758 K. Different approaches such as doping, alloying, hetero-structuring, and different growth methods were implemented to achieve the good thermoelectric performance of the SnSe thin film so far. 28,[46][47][48][49][50][51][52][53][54] Recently, a composite of SnSe and AgSbTe 2 with doped Pb showed a very high power factor of 13 mW cm À1 K À2 at 723 K. 55 They have optimized the thermoelectric transport properties, which can be related to simultaneously suppressing lattice and electronic thermal conductivities by doping Pb.…”

Thermoelectric Property of SnSe Films on Glass Substrate: Influence of Columnar Grain Boundary on Carrier Scattering

“…The n-type Bi-doped SnSe films have been fabricated on the single-crystal substrate using PLD. 27 Highly controlled nanostructures can be fabricated when the films are prepared with nonequilibrium conditions in PLD. Actually, Bi nanoprecipitates with a size of 2 nm, which are expected to reduce the thermal conductivity by scattering the phonons, have been finely dispersed in Bi-SnSe films.…”