Thermoradiative cells are solid-state devices that generate electricity by emitting infrared photons into a colder environment, essentially functioning as “solar cells in reverse” and enabling power production even at night.nature+1
Principle of Operation
Thermoradiative cells are based on a p-n junction semiconductor, similar to photovoltaic cells, but they radiate energy away as thermal infrared photons to a cooler environment rather than absorbing sunlight. When these cells are heated to a temperature above their surroundings, thermally excited charge carriers recombine and emit photons, generating a reverse-bias voltage and electrical current across an external circuit. This process enables the direct conversion of low-grade heat into electricity.ntrs.nasa+3
Efficiency and Limitations
The efficiency of thermoradiative cells is determined by the bandgap of their semiconductor material, the temperature difference between the cell and its environment, and the spectral properties of their emission. Ideal materials have very low bandgap energies (less than 0.1 eV) to optimize emission when cell temperatures are around room temperature at night. Near-field designs, where the cell is placed very close to a suitable heat sink, can further enhance efficiency by exploiting narrowband photon extraction mechanisms. While current efficiency is below the Carnot limit, optimizations such as narrowband emission and multijunction architectures can improve power output and conversion efficiency.optica-opn+2
Applications and Future Prospects
Thermoradiative cells are primarily seen as means to harvest low-grade (“waste”) heat and as a potential approach for nighttime power generation, leveraging the Earth’s warmth radiating to the cold sky. They are being researched for use in space power generation and ground-based renewable energy applications. Advances in material science and engineering are expected to improve their practical efficiency and deployment in future energy systems.