Near- to far-infrared omnidirectional spectral control of thermal emission via transition metal chalcogenide polaritonics for thermophotovoltaics

Omnidirectional spectral thermal emission control over broad infrared wavelengths from the near-infrared (NIR) to the long-wavelength infrared (LWIR) range and over a large angular range has been one of the most sought-after fundamental challenges. For thermophotovoltaics, out-of-band radiation by phonon polaritons in the LWIR range can cause significant efficiency loss, and the lack of omnidirectionality at large angles can cause substantial power density drop. Here, we address these two issues by proposing a materials system based on transition metal chalcogenides (TMCs) and a multi-objective optimization design guideline empowered by hierarchical sequential learning. The inherent exciton and phonon properties of MoS2 enable the modulation of spectral and directional emission across the NIR to LWIR range and large angles of emission through plasmon and phonon polaritons. We fabricate a 6-in. thermal emitter (denoted as Omni-TMC) with omnidirectional high emissivity in the in-band range, an angular-independent sharp cutoff near the band edge, and a quenched emissivity in the entire out-of-band wavelengths across the NIR to LWIR range. The projected power conversion efficiency and power density of the Omni-TMC-based thermophotovoltaic device could reach 46.5% and 4.32 W/cm2, respectively. Our work establishes a versatile materials system and a design guideline not only for thermophotovoltaic emitters but also provides promising solutions for wide-range infrared optical and energy devices.