(a) A collection of 2-level atoms; (b) a 2-level energy system illuminated by photons; (c) the Bose-Einstein distribution.
(a) The energy band for the 2-level system; (b) the energy flux balance of a “photon engine.”
An ensemble of non-interacting 2-level systems having different energy gaps.
An ensemble of interacting 2-level systems having different energy gaps.
(a) A single state occupied by a photon (approximately) normally incident from the sun; (b) momentum scattering of the photon inside the solar cell. Note that the photon incidence and re-emission problem is intrinsically three-dimensional, as the atoms can absorb and reradiate in 3D patterns; the 2D scheme shown above is used to illustrate the concept of angle entropy.
(a) Angle broadening of incident photons using a solar concentrator; (b) a scheme limiting the emission angle of the PV system.
Schematic diagram showing the operation of an excitonic solar cell.
A PV system isotropically illuminated by LEDs.
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