Multiple exciton generation

In a material with carrier multiplication, high-energy photons excite on average more than one electron across the band gap, and so in principle the solar cell can produce more useful work.

The quantum mechanical origin of MEG is still under debate and several possibilities have been suggested:[1] All of the above models can be described by the same mathematical model (density matrix) which can behave differently depending on the set of initial parameters (coupling strength between the X and multi-X, density of states, decay rates).

[5] Multiple exciton generation was first demonstrated in a functioning solar cell in 2011, also using colloidal PbSe quantum dots.

[6] Multiple exciton generation was also detected in semiconducting single-walled carbon nanotubes (SWNTs) upon absorption of single photons.

[8] Double-exciton generation has additionally been observed in organic pentacene derivatives through singlet exciton fission with extremely high quantum efficiency.

Breakdown of the causes for the Shockley-Queisser limit . The black height is Shockley-Queisser limit for the maximum energy that can be extracted as useful electrical power in a conventional solar cell. However, a multiple-exciton-generation solar cell can also use some of the energy in the green area (and to a lesser extent the blue area), rather than wasting it as heat. Therefore it can theoretically exceed the Shockley-Queisser limit.