Relationship between thermoelectric figure of merit and energy conversion efficiency

Hee Seok Kim, Weishu Liu, Gang Chen, Ching Wu Chu, Zhifeng Ren

Research output: Contribution to journalArticlepeer-review

407 Citations (Scopus)


The formula for maximum efficiency (ηmax) of heat conversion into electricity by a thermoelectric device in terms of the dimensionless figure of merit (ZT) has been widely used to assess the desirability of thermoelectric materials for devices. Unfortunately, the ηmax values vary greatly depending on how the average ZT values are used, raising questions about the applicability of ZT in the case of a large temperature difference between the hot and cold sides due to the neglect of the temperature dependences of the material properties that affect ZT. To avoid the complex numerical simulation that gives accurate efficiency, we have defined an engineering dimensionless figure of merit (ZT)eng and an engineering power factor (PF)eng as functions of the temperature difference between the cold and hot sides to predict reliably and accurately the practical conversion efficiency and output power, respectively, overcoming the reporting of unrealistic efficiency using average ZT values.

Original languageEnglish
Pages (from-to)8205-8210
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number27
Publication statusPublished - 2015 Jul 7

All Science Journal Classification (ASJC) codes

  • General


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