Publication date: 22nd July 2026
Focusing light with lenses played a pivotal role in the development of modern science, particularly in physics, biology and astronomy. Passive (non-absorbing) lenses are only able to focus direct (collimated) light and therefore cannot concentrate light from the thermodynamic perspective: any decrease in spatial extent must be compensated by an increase in the angular extent of the light beam to satisfy the second law of thermodynamics. This makes it impossible to use a lens to increase the brightness (photons Sr-1m-2s-1eV-1) of a beam. This is fundamentally one of the reasons lasers are so useful: they provide a high brightness light source. Lasing, however, is not the only mechanism to concentrate light. In principle light absorbing (active) lenses are capable of not only focusing but also concentrating light, increasing the brightness of a source. In order to satisfy thermodynamics, these lenses must compensate the increase in brightness (optical concentration) with a decrease in the photon energy (Stokes shift).[1] Although this principle has been experimentally validated, the performance of these luminescent concentrators falls remarkably short of their thermodynamic potential: all demonstrations of light concentration beyond 4X can improve theoretically by at least a factor of a million. This enormous gap between the thermodynamic and practical limit of light concentration stems from the requirement of emitted light to travel long distances through a strongly absorbing waveguide. Higher concentration factors require longer distances, which unavoidably magnify reabsorption and scattering losses. We propose a novel approach using carrier funneling and luminescent collimation, which decouples concentration from emission propagation distance, breaking the major practical limitation of luminescent concentrators. Finite-difference time-domain, transport and recombination simulations combined with realistic material properties of mixed halide perovskite film/microlens arrays demonstrate concentration factors above 290x, reaching more than 14% of the thermodynamic limit.
The work was performed at the NWO institute AMOLF. E.C.G. received funding from the European Research Council (ERC).
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