1. Materials Research Laboratory, Samsung Advanced Institute of Technology, Yongin 446-712, Korea


2. Department of Physics, Sung Kyun Kwan University, Suwon 440-746, Korea


3. Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea


4. Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854-8019, USA

Correspondence to: Sang Mock Lee¹ Correspondence and requests for materials should be addressed to S.M.L. (Email: sangmocklee@samsung.com).

Thermoelectric energy harvesting—the transformation of waste heat into useful electricity—is of great interest for energy sustainability. The main obstacle is the low thermoelectric efficiency of materials for converting heat to electricity, quantified by the thermoelectric figure of merit, ZT. The best available n-type materials for use in mid-temperature (500–900 K) thermoelectric generators have a relatively low ZT of 1 or less, and so there is much interest in finding avenues for increasing this figure of merit¹. Here we report a binary crystalline n-type material, In₄Se_3-, which achieves the ZT value of 1.48 at 705 K—very high for a bulk material. Using high-resolution transmission electron microscopy, electron diffraction, and first-principles calculations, we demonstrate that this material supports a charge density wave instability which is responsible for the large anisotropy observed in the electric and thermal transport. The high ZT value is the result of the high Seebeck coefficient and the low thermal conductivity in the plane of the charge density wave. Our results suggest a new direction in the search for high-performance thermoelectric materials, exploiting intrinsic nanostructural bulk properties induced by charge density waves.