Few-layer Bi2O2Se: A promising candidate for high-performance near-room-temperature thermoelectric applications.

Advancements in high-temperature thermoelectric materials have been substantial, yet identifying promising near-room-temperature candidates for efficient power generation from low-grade waste heat or thermoelectric cooling applications has become critical but proven exceedingly challenging. Bismuth oxyselenide (Bi2O2Se) emerges as an ideal candidate for near-room-temperature energy harvesting due to its low thermal conductivity, high carrier mobility and remarkable air-stability. In this study, the thermoelectric properties of few-layer Bi2O2Se over a wide temperature range (20 - 380 K) are investigated, where a charge transport mechanism transitioning from polar optical phonon (POP) to piezoelectric scattering at 140 K is observed. Moreover, the Seebeck coefficient (S) increases with temperature up to 280 K then stabilizes at ~-200 μV/K through 380 K. Bi2O2Se demonstrates high mobility (450 cm2V-1s-1) within the optimum power factor (PF) window, despite its T^(-1.25) dependence. The high mobility compensates the minor reduction in carrier density n2D hence contributes to maintain a robust electrical conductivity ~3x104 S/m. This results in a remarkable PF of 860 μW m-1K-2 at 280 K without the necessity for gating (Vg = 0 V), reflecting the innate performance of the as-grown material. These results underscore the considerable promise of Bi2O2Se for room temperature thermoelectric applications.