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Thermoelectric coolers utilizing the Peltier effect have dominated the field of solid‐state cooling but their efficiency is hindered by material limitations. Alternative routes based on the Thomson and Nernst effects offer new possibilities. Here, we present a comprehensive investigation of the thermoelectric properties of 1T‐TiSe₂, focusing on these effects around the charge density wave transition (≈200 K). The abrupt Fermi surface reconstruction associated with this transition leads to an exceptional peak in the Thomson coefficient of 450 μV K⁻¹at 184 K, surpassing the Seebeck coefficient. Furthermore, 1T‐TiSe₂exhibits a remarkably broad temperature range (170–400 K) with a Thomson coefficient exceeding 190 μV K⁻¹, a characteristic highly desirable for the development of practical Thomson coolers with extended operational ranges. Additionally, the Nernst coefficient exhibits an unusual temperature dependence, increasing with temperature in the normal phase, which we attribute to bipolar conduction effects. The combination of solid–solid pure electronic phase transition to a semimetallic phase with bipolar transport is identified as responsible for the unusual Nernst trend and the unusually large Thomson coefficient over a broad temperature range. 

In 1T-TaS2−xSex, the charge density wave (CDW) state features a star of David lattice that expands across layers as the system becomes commensurate upon cooling. The layers can also order along the c-axis, and different stacking orders have been proposed. Using neutron scattering on powder samples, we compared the stacking order previously observed in 1T-TaS2 when the system is doped with Se. While at low temperature, a 13c layer sequence stacking was observed in TaS2; this type of ordering was not evident with doping. Doping with Se results in a metallic state in which the Mott transition is suppressed, which may be linked to the absence of layer stacking.