Defect Engineering in Solution-Processed Polycrystalline SnSe Leads to High Thermoelectric Performance.

Yu Liu,Seungho Lee,Maria Chiara Spadaro,Maria Ibáñez,Tanmoy Ghosh,Mariano Calcabrini,Yuan Yu,Chenyang Xie,Jordi Arbiol,Oana Cojocaru-Mirédin,Cheng Chang,Jérémy David

doi:10.1021/acsnano.1c06720

Abstract

SnSe has emerged as one of the most promising materials for thermoelectric energy conversion due to its extraordinary performance in its single-crystal form and its low-cost constituent elements. However, to achieve an economic impact, the polycrystalline counterpart needs to replicate the performance of the single crystal. Herein, we optimize the thermoelectric performance of polycrystalline SnSe produced by consolidating solution-processed and surface-engineered SnSe particles. In particular, the SnSe particles are coated with CdSe molecular complexes that crystallize during the sintering process, forming CdSe nanoparticles. The presence of CdSe nanoparticles inhibits SnSe grain growth during the consolidation step due to Zener pinning, yielding a material with a high density of grain boundaries. Moreover, the resulting SnSe–CdSe nanocomposites present a large number of defects at different length scales, which significantly reduce the thermal conductivity. The produced SnSe–CdSe nanocomposites exhibit thermoelectric figures of merit up to 2.2 at 786 K, which is among the highest reported for solution-processed SnSe.

Highlights

Materials able to reversibly convert heat into electricity, i.e., thermoelectric materials, require high electrical conductivity (σ), high Seebeck coefficient (S), and low thermal conductivity (κ)
SnSe particles were prepared in water, using Se powder and tin chloride hydrate as precursors.[37]
In the case of SnSe−CdSe nanocomposites, SnSe particles were mixed with CdSe molecular complexes (x mol %; x = 1, 2, 3, and 4) in Nmethyl formamide for 48 h before annealing

Summary

Introduction

Materials able to reversibly convert heat into electricity, i.e., thermoelectric materials, require high electrical conductivity (σ), high Seebeck coefficient (S), and low thermal conductivity (κ). The optimization of these three strongly interrelated properties involves tuning the electronic structure of the material and the charge and phonon scattering mechanisms.[1−4]. The problem is that polycrystalline SnSe suffers from lower thermoelectric performance due to oxidation leading to higher thermal conductivities, partial loss of anisotropy diminishing electrical conductivity, and imprecise control of the doping level.[16,17]. Different approaches to overcome these limitations include chemical reduction of oxide species,[16,17] liquid-phase compaction[18] and hot deformation processes to promote texture,[19] and doping control with different alkali (K, Na, and Li)[20−22] and transition (Ag, Cu, Zn, and Cd) metals.[23−29] approaches have been scrutinized to further enhance the polycrystalline materials’ performance, such as alloying with SnS,[30] Pb, and Ge32 and the introduction of different nanofeatures such as nanoporous or nanoprecipitates (i.e., InSey,[33] AgSnSe2,34 PbSe,[35] and Ag8SnSe636)

Methods

Results

Conclusion