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.