Hot Carrier Dynamics in Photovoltaic Systems

Hot carrier dynamics in photovoltaic systems revolve around the behaviour of photogenerated electrons and holes that possess excess kinetic energy above the band-edge equilibrium. Rather than immediately thermalising with the lattice, these carriers can be harnessed to exceed the conventional efficiency limits of solar cells. Central to this endeavour is the mitigation of rapid energy loss via phonon emission, often addressed through nanostructured architectures such as quantum wells, energy-selective contacts and phononic engineering. By prolonging the lifetime and preserving the temperature of hot carriers, it becomes possible to extract charge at higher voltages, reduce thermalisation losses and unlock new pathways for high-efficiency and thermophotonic devices. Global significance spans from large-scale solar farms to integrated electronic-photonic systems, underscoring the practical imperative of controlling carrier–phonon interactions and energy-filtering mechanisms.

Research from Nature Portfolio

Recent studies have illuminated the complex interplay of phonon dynamics and carrier scattering in quantum-well systems. A 2023 investigation of InGaAs/InGaAsP multi-quantum wells revealed that nonequilibrium longitudinal optical phonons dominate the initial heating of carriers, with Pauli exclusion and pronounced intervalley transfer significantly altering steady-state temperatures. Ensemble Monte Carlo simulations coupled with photoluminescence measurements demonstrated pathways to suppress energy loss, suggesting routes to limit thermalisation in high-density regimes. A 2021 analysis of InAs/AlAsSb multiple-quantum wells used terahertz probing to capture multi-stage decay processes, identifying metastable states and defect-mediated Auger scattering as levers to extend hot-carrier lifetimes. Foundational work from 2018 on type-II quantum wells showed that inhibited phonon coupling at heterointerfaces can lengthen electron thermalisation to nanoseconds by mismatching phonon dispersions, thereby stabilising hot distributions at room temperature.

Hot Carrier Dynamics in Photovoltaic Systems publication trend

The graph below shows the total number of articles in hot carrier dynamics in photovoltaic systems across all publications each year (not limited to Nature Index journals).

Technical terms

Hot carrier: An electron or hole with kinetic energy substantially above thermal equilibrium, generated by the absorption of high-energy photons.

Phonon thermalisation: The process by which hot carriers dissipate energy to the lattice via emission and reabsorption of phonons.

Multiple-quantum well (MQW): A nanostructure formed by alternating thin semiconductor layers that confine carriers in discrete energy states, slowing thermalisation.

Intervalley scattering: Carrier transfer between different minima (valleys) in the conduction band, influencing energy distribution and cooling rates.

Detailed balance: A framework equating absorption and emission processes to model photovoltaic performance and guide efficiency optimisation.

References

1. The role of nonequilibrium LO phonons, Pauli exclusion, and intervalley pathways on the relaxation of hot carriers in InGaAs/InGaAsP multi-quantum-wells. Scientific Reports (2023).
2. Hot-carrier dynamics in InAs/AlAsSb multiple-quantum wells. Scientific Reports (2021).
3. Enhanced hot electron lifetimes in quantum wells with inhibited phonon coupling. Scientific Reports (2018).
4. Theory of non-equilibrium ‘hot’ carriers in direct band-gap semiconductors under continuous illumination. New Journal of Physics (2022).
5. Detailed balance calculations for hot-carrier solar cells: coupling high absorptivity with low thermalization through light trapping. EPJ Photovoltaics (2019).
6. Current–voltage curves and operational stability in hot-carrier solar cell. Journal of Applied Physics (2020).