Highly integrated GeTe thin-film thermoelectric devices for extreme environments

Thermoelectric thin films offer promising potential for self-powered device applications. However, their low integration density poses a significant challenge in achieving high electrical output. Herein, we present a highly integrated, vertically structured thermoelectric thin-film device comprising p-type Ge_0.98Bi_0.02Te and n-type Ag₂Se films. The optimized Ge_0.98Bi_0.02Te films exhibit a high room-temperature power factor of ∼26.1 μW cm⁻¹ K⁻², attributed to the effective reduction in carrier concentration by Bi doping. When coupled with a self-cleaning solar absorber, the device efficiently captures solar energy, establishing a pronounced temperature difference of 32 K across the thermoelectric legs under outdoor conditions. This configuration delivered a high open-circuit voltage density of ∼25.7 mV cm⁻² and a power density of ∼2.5 mW cm⁻² in Shenzhen China (114.31° E, 22.59° N) on June 2, 2025, due to the superior room-temperature TE performance of both Ge_0.98Bi_0.02Te and Ag₂Se films, as well as a high device integration density of ∼4.4 pair per cm². Moreover, the self-cleaning solar absorber enhances environmental resilience, enabling consistent performance even under harsh desert conditions. These findings underscore the potential of GeTe-based thermoelectric thin films for sustainable energy harvesting and power generation, particularly in extreme climates.