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A validated SPICE network simulation study on improving tunnel diodes by introducing lateral conduction layers
|Progress in Photovoltaics 20 (2012), No.3, pp.274-283|
| Journal Article|
|Fraunhofer ISE ()|
In this work, network simulations using LTSpice (Linear Technology, Milpitas, CA, USA) for monolithic triple-junction solar cells have been performed. In order to simulate the internal structure correctly, the integration of the tunnel diode into the network simulation was mandatory. The tunnel-diode characteristics are modeled by LTSpice's arbitrary behavioral current sources. The integration of tunnel-diode characteristics into the network model was validated by comparison of simulated and experimental data. Lattice-matched triple-junction solar cells were examined under homogenous illumination between 1 and 1900suns as well as under non-uniform digital irradiance. The verified model was then used to study the influence of lateral current spreading in layers surrounding the tunnel diodes. It is shown that a lateral current spreading from high to low illumination intensity regions cannot prevent the tunnel diode from switching to thermal diffusion under the used Gaussi anillumination profile as it appears in concentrator photovoltaic applications. Furthermore, resistance regimes of the lateral conducting layers were identified, which would enable a current spreading that is high enough to transport all current exclusively by tunneling. It is shown that the presence of at least one additional layer above and one below the tunnel diode is mandatory. Finally, the necessary layer thicknesses using Alx-1GaxAs as lateral conducting layers are calculated for different doping concentrations and mole fractions x.