Few-layer Bi 2 O 2 Se: a promising candidate for high-performance near-room-temperature thermoelectric applications.

Advancements in high-temperature thermoelectric (TE) materials have been substantial, yet identifying promising near-room-temperature candidates for efficient power generation from low-grade waste heat or TE cooling applications has become critical but proven exceedingly challenging. Bismuth oxyselenide (Bi 2 O 2 Se) 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 TE properties of few-layer Bi 2 O 2 Se over a wide temperature range (20-380 K) are investigated, where a charge transport mechanism transitioning from polar optical phonon to piezoelectric scattering at 140 K is observed. Moreover, the Seebeck coefficient ( S ) increases with temperature up to 280 K then stabilizes at∼-200 μ V K -1 through 380 K. Bi 2 O 2 Se demonstrates high mobility (450 cm 2 V -1 s -1 ) within the optimum power factor (PF) window, despite itsT-1.25dependence. The high mobility compensates the minor reduction in carrier density n 2D hence contributes to maintain a robust electrical conductivity∼3 × 10 4 S m -1 . This results in a remarkable PF of 860 μ W m -1 K -2 at 280 K without the necessity for gating ( V g = 0 V), reflecting the innate performance of the as-grown material. These results underscore the considerable promise of Bi 2 O 2 Se for room temperature TE applications.