Generalized detailed balance theory of solar cells
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Beschreibung
The principle of detailed balance is the requirement that every microscopic process
in a system must be in equilibrium with its inverse process, when the system itself is
in thermodynamic equilibrium. This detailed balance principle has been of special
importance for photovoltaics, since it allows the calculation of the limiting efficiency
of a given solar cell by defining the only fundamental loss process as the radiative
recombination of electron/hole pairs followed by the emission of a photon. In equilibrium,
i.e. in the dark and without applied voltage, the absorbed and emitted
photon flux must be equal due to detailed balance. This equality determines the
radiative recombination from absorption and vice versa. While the classical theory
of photovoltaic efficiency limits by Shockley and Queisser considers only one detailed
balance pair, namely photogeneration and radiative recombination, the present work
extends the detailed balance principle to any given process in the solar cell. Applying
the detailed balance principle to the whole device leads to two major results,
namely (i) a model that is compatible with the Shockley-Queisser efficiency limit for
efficient particle transport, while still being able to describe non-ideal and non-linear
solar cells, and (ii) an analytical relation between electroluminescent emission and
photovoltaic action of a diode that is applied to a variety of different solar cells.
This thesis presents several variations of a detailed balance model that are
applicable to different types of solar cells. Any typical inorganic solar cell is a
mainly bipolar device, meaning that the current is carried by electrons and holes.
The detailed balance model for pn-type and pin-type bipolar solar cells is therefore
the most basic incorporation of a detailed balance model. The only addition compared
to the classical diode theory or compared to standard one-dimensional device
simulators is the incorporation of photon recycling, making the model compatible
with the Shockley-Queisser limit and the classical diode theory
Autor*in
Thomas Kirchartz
Themen in »Generalized detailed balance theory of solar cells«
Detailed balance Shockley-Queisser Solar Cells