Carrier Funneling and Luminescent Collimation for Extreme Diffuse Light Concentration

Passive (nonabsorbing) 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. In principle, light-absorbing (active) lenses can compensate the increase in brightness (optical concentration) with a decrease in the emitted photon energy (Stokes shift). The performance of such luminescent concentrators falls remarkably short of their thermodynamic potential: all demonstrations of light concentration beyond 4× can improve theoretically by at least a factor of a million. This enormous gap between the thermodynamic and practical limits 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 calculations combined with realistic material properties of mixed halide perovskite film/microlens arrays demonstrate concentration factors above 290×, reaching more than 14% of the thermodynamic limit.

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