This paper develops three dimensional numerical models of a two-stage series-connected TEC model and a two-stage parallel-connected TEC model. NSGA-Il is used to optimize their electric current, height of lower stage and ratio of channel width and thickness of fin in the case of constant thermoelectric material volume. Two objectives, exergy efficiency and irreversibility are considered simultaneously. The optimal values one Pareto front are obtained by three decision making methods, Shannon's entropy, TOPSIS and LINMAP, while deviation index is a criterion for evaluating three decision making methods. Sensitive analysis has been carried out to investigate the influence of three variables to be optimized. And TEC with and without plate-fin heat exchanger have been compared. The results show that solution selected by LINMAP is the most compromising solution. The parallel connected TEC saves about 50% of the power consumption compared to the series connected TEC under the same temperature difference. Optimal variables are discussed to obtain the most energy efficient solution with optimal configuration and plate-fin heat exchanger. (C) 2019 Elsevier Ltd. All rights reserved.