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  1D Tandem solar cell




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Cascade solar cell (Tandem solar cell)

Author: Stefan Birner

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Cascade solar cell (Tandem solar cell)


Here, we solve the Poisson equation in an AlGaAs/InGaAs monolithic cascade solar cell (tandem solar cell).

The layout is based on US patent 4,179,70: Cascade solar cell

See also the following publication for more details:

Computer Modeling of a Two-Junction, Monolithic Cascade Solar Cell
M.F. Lamorte, D.H. Abbott
IEEE Transactions on Electron Devices 27 (1), 231 (1980)


The following figure shows the conduction band edge and the valence band edges (heavy hole, light hole and split-off hole) of this solar cell at zero bias.
The built-in potential has been calculated to be 1.83 V.
At the left side (region 1), a graded p-type AlGaAs layer has been used to generate an electric field of 3 kV / cm (= 30 meV / 100 nm).
We assumed that all materials are strained with respect to the GaAs substrate, thus the degeneracy of heavy and light hole valence band edges is lifted, especially inside the InGaAs regions.


The band gap as a function of distance is shown in the following figure. This data can be found in this file: BandGap1D.dat


Here, the electron and hole densities are plotted.


Tunnel junction

The area around the tunnel junction which is in the middle of the device at ~2100 nm is shown in this plot:


The electron and hole densities in the vicinity of the tunnel junction are shown in this graph.
Note that the density has been calculated classically (without solving the Schrödinger equation, i.e. without quantum mechanics).