Analytic computation of the photocurrent density in a n-6H-SiC/p-Si/n-Si/p-Si0.8Ge0.2 multilayer solar cell

In this work we conceived a model of a multilayer solar cell composed by four layers of opposite conductivities: an n-type 6H-SiC used as a frontal layer to absorb high energy photons (energy gap equals 2.9 eV), a p-type Si layer, an n-type Si layer and a p-type SiGe back layer to absorb low energy photons (Si_0.8Ge_0.2 with an energy gap equal to 0.8 eV). The impurity concentration in every layer of the model is taken equal to 10¹⁷ cm⁻³ to ensure abrupt junctions inside the cell. The optical properties of the separate layers have been fitted and tabulated to be used for thin films devices numerical simulation. We developed the equations giving the minority carrier concentration and the photocurrent density in each abscissa of the model. We used Matlab software to simulate and optimize the layers thicknesses to achieve the maximum photocurrent generated under AM0 solar spectrum. The results of simulation showed that the optimized structure could deliver, assuming 10⁵ cm/s surface recombination velocity, a photocurrent density of more than 53 mA/cm², which represents 88.3% of the ideal photocurrent (59.99 mA/cm²) that can be generated under AM0 solar spectrum.