Waste heat, an abundant energy source generated by both industries and nature, has the potential to be harnessed into electricity via thermoelectric power generation. The performance of thermoelectric modules, typically composed of cuboid-shaped materials, depends on both the materials' intrinsic properties and the temperature difference created. Despite signi cant advancements in the development of e cient materials, macroscopic thermal designs capable of accommodating larger temperature differences have been largely underexplored because of the challenges associated with processing bulk thermoelectric materials. Herein, we present the design strategy for Cu 2 Se thermoelectric materials for high-temperature power generation using a combination of nite element modelling and 3D printing. The macroscopic geometries and microscopic defects in Cu 2 Se materials are precisely engineered by optimising the 3D printing and post-treatment processes, leading to signi cant enhancements in the material e ciency and temperature difference within devices, where the hourglass geometry exhibits maximised output powers. The proposed approach paves the way for designing e cient thermoelectric power generators.