Wavelength-selective thermal extraction for higher efficiency and power density thermophotovoltaics

Thermophotovoltaics have long been of interest as an energy conversion technology but suffer from low power density and low efficiency. Structured emitters designed to alter the emission spectrum and increase the efficiency are not stable at the necessary high emitter temperatures and also reduce the power density. Here, we propose a wavelength-selective thermal extraction device that mitigates these challenges and demonstrate a transfer-printing process needed to fabricate the device. The device consists of a ZnS solid hemisphere with a patterned thin film optical filter that passively increases the far-field radiated flux from an emitter within a wavelength band near the bandgap of a photovoltaic cell. Crucially, the device does not need to be in physical contact with the emitter and thus can be maintained at a lower temperature, circumventing the thermal stability challenge. Our work helps one to address long-standing issues with applications of thermophotovoltaics