What Is Thermalization?
Thermalization is the process by which an excited electron or hole loses excess energy and relaxes toward the band edge after absorption. In a semiconductor, that lost energy is transferred to the crystal lattice as heat, so energy carried by a high-energy photon is only partly available for electrical work in the circuit.
In photovoltaic energy-conversion physics, thermalization occurs whenever a photon carries more energy than the material needs to cross its threshold. The excess above the Bandgap does not become extra voltage; it is usually dissipated through rapid interactions with the lattice.
A short expression is E_loss = E_photon – E_g for each absorbed photon above the threshold. Why it matters is that this loss channel is one reason single-junction cells cannot convert most of the solar spectrum efficiently, even when their absorption of incoming light is otherwise strong.
Used in devices include solar cells, photodetectors, and semiconductor lasers. Researchers study thermalization times with ultrafast spectroscopy because slowing carrier cooling could improve hot-carrier devices and help nanostructures preserve more of the incoming photon energy before electrical extraction.
Example:
A blue photon absorbed in silicon creates a charge carrier, but much of its extra energy quickly becomes heat through thermalization.
Related Concepts:
- Bandgap
- Hot Carrier
- Quantum Dot