  Enhancing the absorption and emission of electromagnetic waves over a broad
range of wavelengths is a topic of fundamental and applied interest in
photonics and energy research. In the context of light trapping in solar cells,
for example, significant interest in the past decade has focused on overcoming
limits in the ray-optics regime with nanophotonic structures. However, many
such structures, in particular plasmonic structures, or PT-symmetric systems
can posses multiple materials with varying values of intrinsic loss. Here, we
rigorously determine the effect of parasitic loss on the achievable absorption
enhancement in arbitrary electromagnetic structures. We show that the
fundamental limit of broadband absorption enhancement, even in the presence of
large parasitic loss in an alternate material, can exceed conventional
ray-optics limits on light trapping and absorption enhancement. We numerically
verify this behavior by determining the absorption enhancement factor of a
canonical system, a metal-insulator-metal waveguide, whose core is a low-index
organic semiconductor, in the presence of varying intrinsic loss values in the
metal.
