  To achieve thermoelectric energy conversion, a large transverse
thermoelectric effect in topological materials is crucial. However, the general
relationship between topological electronic structures and transverse
thermoelectric effect remains unclear, restricting the rational design of novel
transverse thermoelectric materials. Herein, we demonstrate a topological
transition-induced giant transverse thermoelectric effect in polycrystalline
Mn-doped Mg3+{\delta}Bi2 material, which has a competitively large transverse
thermopower (617 uV/K), power factor (20393 uWm-1K-2), magnetoresistance
(16600%), and electronic mobility (35280cm2V-1S-1). The high performance is
triggered by the modulation of chemical pressure and disorder effects in the
presence of Mn doping, which induces the transition from a topological
insulator to a Dirac semimetal. The high-performance polycrystalline Mn-doped
Mg3+{\delta} Bi2 described in this work robustly boosts transverse
thermoelectric effect through topological phase transition, paving a new avenue
for the material design of transverse thermoelectricity.
