"V approaches zero"

A heated semiconductor light-emitting diode at low forward bias voltage V<kBT/q is shown to use electrical work to pump heat from the lattice to the photon field. Here the rates of both radiative and nonradiative recombination have contributions at linear order in V. As a result the device’s wall-plug (i.e., power conversion) efficiency is inversely proportional to its output power and diverges as V approaches zero. Experiments directly confirm for the first time that this behavior continues beyond the conventional limit of unity electrical-to-optical power conversion efficiency.

Read More | "Thermoelectrically Pumped Light-Emitting Diodes Operating above Unity Efficiency" | Parthiban Santhanam, Dodd Joseph Gray, Jr., and Rajeev J. Ram | ?Physical Review Letters?Wired