Rapid Stoichiometry Control in Cu₂Se Thin Films for Room-Temperature Power Factor Improvement

Abstract

Cu 2 Se thin films provide a promising route toward relatively safe, sustainable and solution processed thermoelectric (TE) modules in contrast to more expensive and toxic materials currently on the market such as Bi 2 Te 3. Cu 2 Se is known in the TE community for its high performance at high temperature and has recently attracted attention from its large theoretically predicted figure of merit at room temperature. Unfortunately, one of the main limitations encountered so far in Cu 2 Se thin films is that the carrier concentrations are not optimized for TE operation after solution processing. In this work, we conduct a comprehensive study of the structural, optical, and TE properties of Cu 2 Se thin films and demonstrate that nonoptimized carrier concentrations in these films lead to observations of poor performance at room temperature. Through a simple soaking procedure in a Cu + ion solution for only a few minutes, we demonstrate a 200− 300% increase in power factor. This soaking process pushes the carrier concentration of the Cu 2 Se thin film toward its optimal value for TE operation and marks the highest TE performance for any solution processed Cu 2 Se thin film at room temperature thus far. If the performance can be further optimized at room temperature, Cu 2 Se thin films will be the material of choice to utilize in TE modules for powering miniature electronics and sensors, which has been an increasingly popular and rapidly expanding market.

High-performance thermoelectric silver selenide thin films cation exchanged from a copper selenide template

“…The Se peak shi may be attributed to the change of Se valence state due to the reduction of Cu vacancies and the occupancy of Ag ions within the lattice. 51 The Ag peaks appearing at $369 eV and at $375 eV illustrate a strong presence of Ag within the thin lm sample aer soaking as shown in Fig. 4b.…”

“…48,49,53 To form a thin-lm NC template, we adopted a method developed by Webber et al which demonstrated that bulk copper chalcogenides such as Cu 2 Se, Cu 2 Te and Cu 2 S can be dissolved in a thiol-amine solution mixture and be cast as thin lms on substrates. 45,51,54,55 However, bulk Ag 2 Se powder fails to do so at ambient conditions (see ESI, Fig. S3 †).…”

“…To demonstrate the applicability of our hypothesis, we start off with a template of Cu 2Àx Se thin lms that was prepared via the method reported in the work of Lin et al 50 The resulting Cu 2Àx Se thin lms are not perfectly stoichiometric when synthesized under these chemical conditions, which is normal for the entire copper chalcogenides family. 24,51 Evidence shows that the vacancies in the lattice actually accelerate the exchange process as they provide alternative pathways for the diffusion of Ag + ions, even at low temperatures. 24,52 We then soaked our Cu 2Àx Se lms into a Ag +rich solution for various amounts of time and annealed our nal samples aerwards as outlined in Fig.…”

Recent Progress of Two-Dimensional Thermoelectric Materials

“…Recently, 2D TMDCs have collected a wide attention due to their special properties and are considered to be the next generation of high-performance thermoelectric materials [70,74,90,[175][176][177][178][179][180]. The measured Seebeck coefficient of single-layer MoS 2 can measure over 30 mV K −1 , providing an ideal candidate material for high-performance thermoelectric devices.…”

Thermoelectric Properties of Cu2Se Nano-Thin Film by Magnetron Sputtering

“…In addition, combined with ion beam, laser or photolithography technology, various artificially defined three-dimensional micro-nano structures can be produced, which is convenient for people to understand the relationship between thermoelectric properties and material structure in essence. Many methods have been reported for preparing Cu 2 Se thin films, such as electrochemical deposition [ 21 , 22 , 23 ], pulsed laser deposition [ 24 , 25 ], spin-coating [ 20 , 26 , 27 ], sputtering [ 28 ], thermal evaporation [ 29 , 30 ], etc. For the influence of these preparation methods on the film and the advantages of magnetron sputtering, please refer to our previous article [ 31 ].…”